BACKGROUND OF THE INVENTION The present invention relates to composite gun barrels for small arms, and in particular, to gun barrel for small arms wherein the gun barrel is made with a composite portion and a metallic portion. More particularly, the present invention relates to such a gun barrel wherein the expansion factors of the composite are correlated so as to achieve desiring firing characteristics, such as accuracy and useful life of the gun barrel.

The use of composites for gun barrels is well known in the art of weapons manufacturing. The composite material is much lighter for the strength provided than are most metals which can be practically used for rifles, machine guns and the like. Composites, however, suffer from several major disadvantages. One significant disadvantage is the composite is difficult to form riflings in to promote desired bullet rotation following firing. Additionally, the hot gases which are produce by combustion of the propellant in the bullet casing are extremely corrosive to the composite.

To overcome these problems, composite/metallic gun barrels were developed. Typically, composite/metallic gun barrels are made from thin- walled cylinders of metal which are overlaid with a composite material. Typically, the metallic portion of the barrel will be less than one-tenth of an inch thick along most of the length of the barrel. The metallic liner serves two major purposes. First, the metallic barrel liner provides a hard, machinable surface for spiral riflings in the liner bore which provide a rotational spin to the bullet during flight and greatly improves accuracy, In contrast, the composite material is not sufficiently hard, is friable, and is otherwise unsuitable for barrel riflings. Second, the metallic barrel liner is used to shield the composite material from the hot, corrosive gasses generated when firing a bullet. As the powder burns to propel the bullet through the barrel, the hot gasses formed by the burning power to propel the bullet contact the liner instead of the composite.

One problem which has developed with barrels having a metallic liner surrounded by composite is that they often fail to maintain consistency when repeatedly fired. As a gun is fired several times in rapid succession, the heat

generated from the firing of each bullet begins to accumulate in the bore. Because the metal liner and the composite materials generally have somewhat different coefficients of expansion when exposed to heat, a barrel heated by repeated firing can quickly loose its accuracy and consistency. In apparent attempts to overcome such problems of the prior art, the present level of skill in the art teaches that it is best to use a composite liner which matches the expansion coefficient of the metal being used in the radial direction. However, as will be appreciated by those skilled in the art, a combination of a composite material and metallic liner with similar expansion coefficients may not provide the desired characteristics in other areas, such as strength and durability. Additionally, the metallic liner used to match the composite material is not necessarily the best liner for the desired purpose.

Thus, there is a need for a composite/metallic barrel which is formed so that the composite, the metal and their expansion coefficients provide desired characteristics during firing. For example, when such a barrel is to be used for sporadic firing where accuracy is key, i.e. a high powered rifle used for hunting, the composite/metallic barrel will have matched coefficients of thermal expansion to prevent uneven expansion or contraction of the barrel from rendering the gun less accurate. In contrast, a gun which rapidly fires rounds and in which accuracy is of less concern, such as a military machine gun, will have a composite/metallic barrel wherein the coefficients of thermal expansion are matched to limit expansion of the barrel and prevent premature wear due to excess friction with the round being fired. Furthermore, the composite and the metallic liner of the barrel can be configured and disposed so that the two are primarily independent of one another (i.e. nonbonded) for a substantial length of the barrel. In such a manner the axial expansion of the composite and metal can be different without causing inconsistent binding of the liner, thus avoiding warpage.

SUMMARY OF THE INVENTION

Thus, it is an object of the present invention to provide a gun barrel made of metal and a composite wherein the gun barrel is resistant to the loss of accuracy or consistency due to repeated firing.

It is an additional object of the present invention to provide a gun barrel for small arms which is lightweight and durable.

It is another object of the present invention to provide a gun barrel which is easy to make, easy to use and is inexpensive.

It is yet another object of the present invention to provide a composite/metallic gun barrel wherein the composite portion of the barrel is configured so as to expand and contract in a substantially similar manner to the metallic portion of the barrel in the radial direction and have nearly 0 coefficient of thermal expansion in the axial direction to facilitate accuracy when the gun barrel is fired.

It is still another object of the present invention to provide an alternate composite/metallic gun barrel wherein the composite portion of the barrel is configured so as to expand and contract in such a manner relative to the metallic portion of the barrel to apply a compressive force for the metallic portion during rapid fire situations, and thereby prevent premature wear. It is still yet another object of the present invention to provide a metallic/composite barrel which allows the metallic and composite portions of the barrel to expand and contract at different rates without creating additional stress within the barrel.

The above and other objects of the invention are realized in specific illustrated embodiments of a composite/metallic gun barrel having expansion characteristics which are correlated with the intended use of the gun barrel to thereby provide improved firing characteristics.

In accordance with a first application of the principles of the present invention, the composite portion and metallic portion have matched coefficients of thermal expansion in the radial direction. The gun barrel is made of a metal cylinder which is overwrapped with one or more composite layers. The composite layers are disposed about the metallic cylinder in such an arrangement

that the coefficient of expansion for the composite material is selected to match the coefficient of expansion for the preselected, preferred metallic liner in the radial direction and have 0 or nearly 0 coefficient of thermal expansion in the axial direction to achieve a desired barrel performance. Thus, the composite material may be disposed so that it expands and contracts in like directions and in like amounts with the metallic cylinder in the radial direction. Adjustment of the coefficient of thermal expansion of the composite allows selection of more favorable liner materials and offers enhanced ability to fine tune to cooperative relationship of the composite with the metal. The exact disposition of the composite material, of course, depends both on the composite material and which metal is used for the metallic cylinder of the gun barrel. The composite and its expansion coefficient are matched with the expansion coefficient of the metallic portion of the barrel in a winding pattern to give the composite an effective expansion coefficient which correlates to that of the metallic liner.

In accordance with the one aspect of the first application of the principles of the present invention, the gun barrel may be coated with a bonding material and then overlaid with the composite material in a winding pattern configured to give the composite material an effective expansion coefficient which is substantially similar to that of the barrel in the radial direction and a nearly 0 coefficient of thermal expansion in an axial direction. ln accordance with another aspect of the first application of the principles of the present invention, the composite material is wound onto a mandrel in a pattern to give it a predetermined coefficient of expansion and then cured. The composite portion of the barrel is then removed from the mandrel and mounted about a metallic portion. The composite material on the mandrel is wound in such a pattern to match that of the barrel, thereby forming a barrel having desired expansion characteristics. The composite/metallic barrel is then mounted to the stock of a gun. In a presently preferred version of the first application of the principles of the present invention, the composite portion of the gun barrel is formed of alternating layers of composite material wherein one layer is hoop or spiral

wound so that the fibers are generally disposed at about a 90 degree angle (+_ 10 degrees) to the long axis of the liner. The next most adjacent layer is overlaid on the hoop/spiral wound layer in a longitudinal placement. Additional layers of composite material disposed in longitudinal orientation may be laid prior to the next hoop/spiral wound layer. Typically, the hoop/ spiral wound layer contains composite material in a ratio of between about 1:8 and 1: 12, and most preferably about 1: 10, (by fiber weight) with the longitudinally placed layers when it is desired to have the composite material match the expansion of a steel barrel liner in the radial direction and nearly 0 coefficient of thermal expansion in the axial direction.

In accordance with a second application of the principles of the present invention, the gun barrel is made of a metal cylinder which is overwrapped with one or more composite layers. The composite layers are disposed about the metallic cylinder in such an arrangement that the coefficient of expansion for the composite material is selected and correlated relative to the coefficient of expansion for a preselected, preferred metal liner in the radial direction so as to restrict excess expansion of the liner in the radial direction, while having nearly 0 coefficient of thermal expansion in the axial direction when the metal liner is heated. By evenly constricting the barrel liner, improved barrel performance is achieved. Thus, the composite material may be laid in such a manner that it restricts the expansion of the metallic cylinder under high use conditions in order to prevent premature wear or over expansion on the barrel due to friction with bullets fired therethrough. Adjustment of the coefficient of expansion in the radial direction of the composite allows selection of more favorable liner material, and offers enhanced ability to fine tune the cooperative relationship of the composite and the metal.

The exact disposition of the composite material, of course, depends both on the composite material and which metal is used for the metallic cylinder of the gun barrel. The composite and its expansion coefficient are correlated with the expansion coefficient of the metallic portion of the barrel in a winding pattern to give the composite an effective expansion coefficient which restricts the liner's expansion.

In accordance with the second application of the principles of the present invention, the gun barrel is coated with a bonding material and then overlaid with the composite material in a winding pattern configured to give the composite material an effective expansion coefficient, which is substantially dissimilar to that of the barrel so as to restrict radial expansion of the barrel, while maintaining nearly 0 coefficient of thermal expansion in the axial direction.

In accordance with another aspect of the second application of the principles of the present invention, the composite material is wound onto a mandrel in a pattern to give it a predetermined coefficient of expansion and then cured. The composite portion of the barrel is then removed from the mandrel and mounted about a metallic portion of the barrel which has a coefficient of expansion which, when constricted by the composite portion of the barrel during firing, provides a desired barrel expansion characteristic. The composite/metallic barrel is then mounted to the stock of a gun. In a presently preferred embodiment of the second application of the invention, the composite portion of the gun barrel is formed of alternating layers of composite material wherein one layer is hoop or spiral wound so that the fibers are generally disposed at about a 90 degree angle C±IO degrees) to the long axis of the liner. The next most adjacent layer is overlaid on the hoop/spiral wound layer in a longitudinal placement. Additional layers of composite material disposed in longitudinal orientation may be laid prior to the next hoop/spiral wound layer. Typically, the ratio of longitudinal fibers to hoop wound (transverse) fibers will be less than 8: 1. As the ratio of axial to hoop decreases, the composite casing limits the amount the metal liner can grow due to radial heat expansion.

A third application of the principles of the present invention includes providing a generally cylindrical metallic barrel liner and a composite barrel casing disposed about an exterior of the metallic barrel liner so that a substantially nonbonded interface exists between the liner and the casing and thus the barrel. In other words, unlike conventional composite/metallic barrels in which a bonding agent is coated about the metallic liner so as to bond the metallic liner and the composite material, the present invention omits the bonding

agent uniformly for substantially the length of the barrel. By substantially is meant more than half of the length of the barrel.

In accordance with one aspect of the third application of the invention, the metallic liner and the composite casing are not bonded along the entire length of the barrel portion. As expansion or contraction of the barrel occurs, the metallic liner is able to expand or contract at a different rate and to a different extent than the composite casing without creating stress in the barrel. Because the metallic liner of the barrel and the composite casing of the barrel are independent and not bonded, the barrel does not deform or warp as do the barrels of the prior art, and the accuracy of the barrel is maintamed. The absence of warpage is due to the fact that the nonbonded composite casing and metallic liner can slide with respect to each other. In the prior art, the bonding agent often cracked or otherwise broke free of parts of the barrel while opposing portions of the barrel remained bonded. The uneven bonding exacerbates problems due to uneven expansion and causes pronounced warping of the gun barrel.

In accordance with another principle of the third application of the present invention, the composite material is attached to the metallic liner adjacent to one end of the barrel, typically adjacent to the chamber of the gun, but not for the remainder of the barrel. Preferably, the bonded segment will be no more than 4 inches, and preferably 2 to 3 inches. The bonded segment adjacent the chamber of the gun allows the two portions of the barrel to be held properly in place, while allowing the metallic liner and composite portion to move freely with respect to one another for the remainder of the barrel. Because of the short length of the bonded segment, the barrel is able to avoid warping and retain its accuracy.

In accordance with another aspect of the third application of the present invention, the composite casing of the barrel is formed on a mandrel separate from the metallic liner. The composite casing is then cured and the mandrel removed. The metallic liner is then slid into the composite casing so as to form a gun barrel in which the metallic liner and the composite casing are not bonded together, or are bonded along only a short segment of the barrel as described above.

In accordance with yet another aspect of the third application of the present invention, the gun barrel is formed by forming a metallic liner and coating the liner with a release agent. The composite material is then overlaid on the metallic liner to form the composite portion of the gun barrel. Once the composite portion has cured, the gun barrel is subjected to pressures, temperatures, et cetera, which cause the bonding material to move or otherwise pull free of the metallic liner for the length of the barrel. When the gun barrel is subjected to changes in temperature, the lack of bonding allows the metallic liner to expand and contract independently from the composite casing of the barrel.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the invention will become apparent from a consideration of the following detailed description presented in connection with the accompanying drawings in which:

FIG. 1 shows a fragmented, side cross-sectional view of a gun barrel having a composite portion and a metallic portion made in accordance with the first application of the principles of the present invention;

FIG. 2 shows an exploded view of the gun barrel shown in FIG. 1; FIG. 3 shows a graph of the coefficient of thermal expansion in longitudinal and transverse directions relative to the angle of winding;

FIG. 4 shows a graph of longitudinal and transverse coefficients of thermal expansion as a function of the amount material placed longitudinally along the barrel versus the amount of material hoop or spiral wound about the barrel at an angle approximately 90 degrees to the long axis of the barrel;

FIG. 5 shows an exploded view of a gun barrel made in accordance with the second application of the principles of the present invention;

FIG. 6 shows a fragmented, side cross-sectional view of a gun barrel made in accordance with the principles of the present invention; FIG. 7 shows a fragmented, side cross-section view of another embodiment of a gun barrel in accordance with the principles of the present invention;

FIG. 8 shows a perspective view of a composite casing of a gun barrel being formed about a mandrel; and

FIG. 9 shows a perspective view of a composite material being filament wound about a metallic barrel liner so as to form a metallic/ composite gun barrel.

DETAILED DESCRIPTION

Reference will now be made to the drawings in which the various elements of the present invention will be given numeral designations and in which the invention will be discussed so as to enable one skilled in the art to make and use the invention. It is to be understood that the embodiments discussed below are exemplary of the principles of the present invention, and are not intended to limit the invention as claimed.

Referring to FIG. 1, there is shown a fragmented, side cross-sectional view of a composite/metallic gun barrel, generally indicated at 8, made in accordance with the principles of the present invention. The gun barrel 8 includes a metallic liner 12, which is most typically made of stainless steel. A stainless steel metallic liner 12 is preferred because it is generally less prone to corrosion than other metallic liners. The metallic liner 12 has a first section 12a which is configured to hold a round of ammunition in a chamber 16 formed by the liner, and an elongate second section 12b which extends substantially all of the remaining length of the barrel 8. The first end 12a is generally thicker than the elongate second section to help withstand the explosive force generated when firing a round of ammunition positioned in the chamber 16. In contrast, the second section 12b is thin so as to keep weight of the barrel 8 to a minimum. The primary purpose of the second, elongate section is to channel the hot, explosive gasses generated by firing the round of ammunition out of the barrel.

A casing 20 made of composite material is wrapped about the metallic liner 12. The casing 20 provides strength to the metallic liner 12, but requires less weight than conventional metal barrels. Thus, a barrel 8 which is stronger and lighter than conventional metallic barrels can be made by combining the

metallic liner 12 and the composite casing 20. The metallic liner 12 is necessary to shield the composite casing 20 from the hot gasses generated when firing rounds of ammunition. These gasses are typically very corrosive to the composite casing 20 and can lead to premature failure if some sort of shielding is not provided.

The composite casing 20 will typically be made of graphite fibers which are coated with an epoxy material. For convenience, graphite "prepreg" will typically be used. Graphite prepreg is material which has been preimpregnated with an epoxy resin. Such a material can come in sheets which are easier to handle than individual graphite fibers.

As will be discussed in detail below, graphite is the preferred material for the composite casing because of its behavior when heated. Unlike most materials which expand when heated, graphite actually contracts longitudinally. By selectively controlling the contraction of the graphite, gun barrels 8 can be manufactured which have expansion characteristics which are matched to those of the metallic liner.

The composite casing 20 has a first section 20a which is disposed adjacent the first section 12a of the metallic liner 12a, and a second section 20b adjacent the second section 12b of the metallic liner. To maintain a generally continuous size for the barrel 8 and to ensure sufficient strength along the entire barrel, the first section 20a of the casing 20 is thin, tapering inverse to a taper of the first section 12a of the metallic liner 12, and the second section is thick so as to provide strength along the elongate second section 12b of the liner.

At the exterior of the metallic liner 12 and the interior of the composite casing 20 is an annular interface 24. This interface may be bonded with epoxy or other adhesives or, as set forth below with respect to FIGs. 6 through 9, may be left substantially unbonded. Either may be done regardless of whether the composite casing 20 is formed on a mandrel, cured and then placed on the metallic liner 12, or the composite casing 20 is formed about and cured on the liner. Both of these approaches to forming the composite/metallic gun barrels 8 will be well known to those skilled in the art.

Disposed about an outer circumference of the composite casing 20 of the gun barrel 8 is an overwrap 28. The overwrap 28 may be a series of helically wound fibers, or preferentially, a knitted or woven cloth made of graphite fibers. Referring now to FIG. 2, there is shown an exploded view of the gun barrel 8 shown in FIG. 1 in accordance with the first application of the principles of the present invention. The gun barrel 8 includes the metallic liner 12, having the first and second sections, 12a and 12b, respectively, and the composite casing 20, which includes a plurality of graphite fibers, generally indicated at 32.

The graphite fibers 32 are generally disposed about the metallic liner in first and second groups of fibers 36 and 40, respectively, which are characterized by their orientation. The first group 36 of fibers is disposed in a first orientation so as to circumscribe the metallic liner 12. This may be accomplished by cutting a sheet of prepreg graphite fibers and wrapping the sheet about the metallic liner 12 so that the fibers form a plurality of hoops disposed at about 90 degree angle to a long axis A-A of the metallic liner. In the alternative, the first layer 36 may be formed from a single graphite fiber which is wrapped in a tight spiral so that the fiber is continuously disposed at about 89 degrees from the long axis A-A. Those skilled in the art will appreciate that other angles can be used, preferably those within +_ 10 degrees of 90 degrees for the radially wound fibers and within ± 10 degrees of the long axis for the longitudinally placed fibers. Thus, when used herein, "hoop winding" or "substantially perpendicular" to the long axis and "generally perpendicular" are intended to include the above identified range for the radially wound fibers. Likewise, "substantially longitudinally" and "generally parallel" to the long axis are intended to cover the above identified range of the longitudinally placed fibers.

In a preferred embodiment of the first application of the principles of the present invention, the metallic barrel liner 12 is first wrapped with a fiberglass scrim cloth 34 coated with epoxy or resin. The scrim cloth 34 acts as an insulator to prevent corrosion between the electrically conductive metallic liner 12 and the electrically conductive graphite portion of the barrel casing 20.

Disposed on the first group 36 of fibers is the second group 40 of fibers which consists of elongate graphite fibers which are disposed parallel to the long

axis A-A of the metallic liner. The elongate fibers of the second group 40 are disposed in a second orientation wherein the fibers are laid side to side about the circumference of the metallic liner 12 so as to form at least one generally continuous layer. Additional layers of fiber may be laid in the second orientation before another first group 36 of fibers are positioned about the second group 40 in the first orientation.

By varying the number of layers in the second group 40 of fibers with respect to each group of fibers disposed in the first orientation, the coefficient of thermal expansion for the composite casing 20 can be regulated to provide desired expansion characteristics. For example, in FIG. 1, the metallic liner 12 is wrapped by a first group 36 forming a single first layer. Eleven layers disposed in the second orientation to form the second group 40 are then overwrapped on the first layer 36. Another first group of fibers 36 disposed in the first orientation is placed about the second group 40, followed by another eleven layers forming another second group 40 of fibers. This alternating arrangement is repeated four to five times at any point along the metallic liner 12.

The eleven to one wrapping of the layers of the second group 40 relative to first group 36 provides a composite casing 20 which has expansion coefficients which closely match those of a stainless steel liner in the radial direction and has nominal or nearly 0 coefficient of thermal expansion in the axial direction. By closely matching the expansion coefficients of the casing 20 to the metallic liner 12 in the radial direction and maintaining nearly 0 coefficient of thermal expansion in the axial direction, the accuracy of the gun barrel 8 is preserved. Such matching between the composite casing 20 and the metallic liner are best achieved in graphite when using a between 8 and 12 layers in the second orientation for every layer in the first orientation. In other words, it is preferable to have about 8 to 12 times the amount of fiber by weight disposed in the second orientation that disposed in the first orientation. Those skilled in the art will appreciate that a 12: 1 to 8: 1, etc. , layer construction need not be used. For example, the layers could be replaced with a woven fabric having ten times the amount of fiber in one direction for every

fiber in a substantially perpendicular direction or different winding angles could possibly be formulated to achieve the same result. Instead of binding the metallic liner 12 and causing it to warp, the composite casing expands and contracts with the gun barrel in the radial direction. Those familiar with composite/metallic gun barrels will appreciate in light of the present disclosure that the close match in coefficients of thermal expansion in the radial direction and nearly 0 coefficient of thermal expansion in the axial direction results in a more accurate gun.

Referring now to FIG. 3, there is shown a graph of the coefficient of thermal expansion in longitudinal (axial) and transverse (radial) directions relative to the angle of winding. The graph includes a first, dashed curve 50 which shows that when the fibers are disposed longitudinally along the metallic lining, i.e. 0 degrees from the long axis of the metallic liner 14 (FIG 2), the longitudinal coefficient of expansion for the fibers is slightly less than zero. In such a position, however, the transverse coefficient of expansion is almost 0.00002, as represented by curve 54. As the lay-up angle of the fibers is changed from 0 degrees to 90 degrees, the longitudinal coefficient of expansion changes from a slight negative to slightly less than +0.00002. The transverse coefficient of expansion, in contrast, decreases from nearly 0.00002 to slightly less than zero. In the center of the two extremes, the two curves cross at a lay-up angle of approximately 45 degrees. In such a position, the composite casing 20 (FIGs. 1 and 2) of the gun barrel 8 (FIGs. 1 and 2) will expand in both longitudinal (axial) and transverse (radial) directions. This is a common lay-up angle used in the prior art. Unfortunately, such a lay-up angle lacks the similar expansion of the metallic liner 12 (FIGs. 1 and 2) available with a high ratio of longitudinal fibers to hoops fibers discussed with respect to FIG. 2. FIG. 4 shows another graph in which the longitudinal coefficient of thermal expansion is shown relative to the percentage of transverse layers (90 degrees) relative to longitudinal layers (0 degrees). Beginning at the left of FIG. 4, there is shown a curve 60 representing the transverse coefficient of thermal expansion for the composite casing 20 (FIGs. 1 and 2). When the casing 20 has little or no fibers which are hoop or spiral wound at an angle close to 90 degrees, the casing has a transverse

coefficient of thermal expansion of nearly 0.00002 in/in/°F. With approximately 10 percent fibers wound at approximately 90 degrees, the transverse coefficient of thermal expansion is about 0.000006 in/in/°F, the same coefficient of expansion as stainless steel, such as that which would be used in the metallic liner 12 of a gun barrel 8.

As the percentage of fibers which are wound at 90 degrees approaches 100 percent, the transverse coefficient of thermal expansion falls to slightly below zero. At such a level, the fibers would actually constrict against a metallic liner reducing the metallic barrel's radial expansion. At the right of FIG. 4, a dashed curve representing the longitudinal coefficient of thermal expansion is indicated at 70. When the fibers of the composite casing 20 (FIGs. 1 and 2) are nearly 100 percent disposed in a 90 degree orientation, the longitudinal coefficient of thermal expansion is between 0.00001 and 0.00002. As the percentage of fibers wound at 90 degrees falls, the longitudinal coefficient of expansion decreases. When all of the fibers in the casing 20 are disposed along the long axis of the metallic liner, the longitudinal coefficient of thermal expansion is slightly less than zero.

If a liner other than stainless steel is desired to be used, the ratio of layers in the second orientation relative to the first orientation need only be modified to create a casing which matches the thermal expansion. Thus, for example, if a liner was chosen which had a transverse thermal expansion of 0.000008, the percentage of fibers in the first orientation (90 degrees) would be reduced. Typically, the casing would have one layer in the first orientation and then twelve to fourteen layers in the second orientation, repeated several times. Referring now to FIG. 5, there is shown an exploded view of a gun barrel

108 made in accordance with the second application of the principles of the present invention. A cross-sectional view of the embodiment shown in FIG. 5 would appear substantially the same as FIG. 1. To the extend feasible, each structure in FIG. 5 which correlates with a structure shown in FIG. 1 is provided with a number 100 greater than the numeric identifiers in FIG. 1. Thus, for example, liner 112 in FIG. 5 is substantially the same as liner 12 in FIG. 1.

Referring specifically to FIG. 5, the gun barrel 108 includes a metallic liner 112, having first and second sections, 112a and 112b, respectively, and a composite casing 120, which includes a plurality of graphite fibers, generally indicated at 132. The graphite fibers 132 are generally disposed about the metallic liner in first and second groups of fibers 136 and 140, respectively, which are characterized by their orientation. The first group 136 of fibers is disposed in a first orientation so as to circumscribe the metallic liner 112. This may be accomplished by cutting a sheet of prepreg graphite fibers and wrapping the sheet about the metallic liner 112 so that the fibers form a plurality of hoops disposed at about 90 degree angle to a long axis A-A of the metallic liner. In the alternative, the first layer 136 may be formed from a single graphite fiber which is wrapped in a tight spiral so that the fiber is continuously disposed at about 89 degrees from the long axis A-A. Those skilled in the art will appreciate that other angles can be used, preferably those within +_ 10 degrees of 90 degrees for the radially wound fibers and within + _. 10 degrees of the long axis for the longitudinally placed fibers. Thus, when used herein, "hoop winding" or "substantially perpendicular" to the long axis and "generally perpendicular" are intended to include the above identified range for the radially wound fibers. Likewise, "substantially longitudinally" and "generally parallel" to the long axis are intended to cover the above identified range of the longitudinally placed fibers.

In a preferred embodiment, the metallic barrel liner 112 is first wrapped with a fiberglass scrim cloth 134 coated with epoxy or resin. The scrim cloth 134 acts as an insulator to prevent corrosion between the electrically conductive metallic liner 112 and the electrically conductive graphite portion of the barrel casing 120.

Disposed on the first group 136 of fibers is the second group 140 of fibers which consists of elongate graphite fibers which are disposed parallel to the long axis A-A of the metallic liner. The elongate fibers of the second group 140 are disposed in a second orientation wherein the fibers are laid side to side about the circumference of the metallic liner 112 so as to form at least one generally

continuous layer. Additional layers of fiber may be laid in the second orientation before another first group 136 of fibers are positioned about the second group 140 in the first orientation.

By varying the number of layers in the second group 140 of fibers with respect to each group of fibers disposed in the first orientation, the coefficient of thermal expansion for the composite casing 120 can be regulated to provide desired expansion characteristics. For example, in FIG. 5, the metallic liner 112 is wrapped by a first group 136 forming a single first layer. A single layer disposed in the second orientation to form the second group 140 is then overwrapped on the first layer 136. Another first group of fibers 136 disposed in the first orientation is placed about the second group 140, followed by another single layer forming another second group 140 of fibers. This alternating arrangement is repeated multiple times at any point along the metallic liner 112.

The one to one (or two to one as shown at 140a) wrapping of the layers of the second group 140 relative to first group 136 provides a composite casing 120 which has expansion coefficients which is smaller than those of a stainless steel liner in the radial direction and has nominal or nearly 0 coefficient of thermal expansion in the axial direction. By forming a composite casing 120 with a consistently smaller expansion coefficient than that of the metallic liner 112 in the radial direction and maintaining nearly 0 coefficient of thermal expansion in the axial direction, the barrel is constricted and is not as prone to erosion during rapid fire situations. Such constriction between the composite casing 120 and the metallic liner are best achieved in graphite when using less than 2 layers in the second orientation for every layer in the first orientation. It is preferable to have about even amounts of fiber by weight disposed in the first and second orientations.

Those familiar with rapid firing guns, such as those commonly referred to as machine guns or automatics, will appreciate that a major concern is the speed with which the barrels deteriorate. When the gun is fired at a high rate, the heat in the barrel causes the metal to expand. The expanded metal allows a bullet passing through the barrel 108 to wobble or bounce from side to side

within the barrel as it is propelled forward. Such movement by the bullet substantially increases friction within the barrel and causes the barrel to wear more rapidly and unevenly, defeating accuracy of flight.

By restricting the expansion of the metallic liner 112, a substantial amount of the increase in friction caused by rapid firing can be eliminated. While limiting expansion of the metallic liner 112 affects accuracy, typically due to uneven binding which causes slight warping in the liner, such restrictive design does provide a countervailing benefit. As the bullet travels down the barrel, it is more likely to spin properly and avoid the friction increasing wobble common in the prior art. The constriction of the metallic liner 112 also has the positive effect of increasing barrel life, due to a decrease in friction. Thus, for rapid fire guns, a composite/metallic gun barrel 108 made in accordance with the principles of the present invention can be made lighter, stronger and longer lasting than those of the prior art while maintaining similar accuracy. Referring back to FIG. 3, the graph shown therein is equally applicable to the second aspect of the present invention as to the first. In the center of the two extremes, the two curves cross at a lay-up angle of approximately 45 degrees. In such a position, the composite casing 120 (FIGs. 1 and 2) of the gun barrel 108 (FIGs. 1 and 2) would expand in both longitudinal (axial) and transverse (radial) directions. This is a common lay-up angle used in the prior art. Unfortunately, such a lay-up angle lacks the similar expansion of the metallic liner 112 (FIGs. 1 and 2) available with the perpendicular placement discussed above. The 45 degree lay-up angle lacks the benefits of a 1 : 1 or similar longitudinal to hoop ratio in the composite casing 120 which sufficiently restricts expansion of the metallic liner without substantial axial expansion.

The graph of FIG. 4 is also applicable to the second applications of the principles of the present invention. As the percentage of fibers which are wound at 90 degrees approaches 100 percent, the transverse coefficient of thermal expansion falls to slightly below zero. At such a level, the fibers would actually constrict against a metallic liner which had not expanded. By using a 1 : 1 or similar ratio, constriction is reserved for significant expansion.

The curve 60 representative of the transverse coefficient of thermal expansion and the curve 70 representative of the longitudinal coefficient of thermal expansion intersect at a point where the casing is formed of an equal amount of fibers disposed in the first orientation (90 degrees) and fibers disposed in the second orientation (0 degrees), as indicated by point 80. In such a balance, the composite casing allows some expansion of the metallic liner, but provides better constriction than a 45 degree lay-up angle as is shown in FIG. 3. Also, the 0/90 lay-up is much stronger in the radial and axial directions than the _ 45° winding. If a liner other than stainless steel is desired to be used, the ratio of layers in the second orientation relative to the first orientation need only be modified to create a casing which constricts the expansion a desired amount. Thus, for example, if a liner was chosen which had a transverse thermal expansion of 0.000008, the percentage of fibers in the first orientation (90 degrees) would be reduced. Typically, the casing would have one layer in the first orientation and then thirteen or fourteen layers in the second orientation, repeated several times.

Referring to FIG. 6, there is shown a composite/ metallic gun barrel, generally indicated at 210, made in accordance with the third application of the principles of the present invention. The composite/ metallic gun barrel 210 has an elongate metallic cylinder 214 which forms a liner for the gun barrel 210.

This metallic liner 214 is typically made of stainless steel, but can be made of other metals as well.

The metallic liner has a first, thin walled portion 214a which extends from an open, first end 218 to a position two to four inches from a second end 222 which forms a chamber 224 for receiving a cartridge 226. From the position at which the first, thin walled portion 214a ends, a second portion 214b of the metallic liner 214 has an increased thickness, as shown in FIG. 6. The thicker walls of the second portion 214b form the chamber 224 for receiving the cartridge 226. The thicker walls also provide additional support to compensate for the explosive force caused by firing the cartridge 226.

Wrapped about the metallic liner 214 is a casing 230 made of a composite material. While the composite material will typically be a graphite "prepreg" ,

or graphite fibers coated with epoxy, other composite fibers and/or resins may be used as is known to those skilled in the art. The casing 230 has a first, thick walled section 230a which extends along the barrel 210 for the length of the first, thin walled portion 214a of the metallic liner 214. Adjacent the second portion 214b of the metallic liner 214, a second section 230b tapers to a thinner wall to match the increase in thickness in the metallic liner 214.

At the exterior circumference of the metallic liner 214 and the interior circumference of the composite casing 230 is an interface 234. In prior art composite/metallic gun barrels, the metallic liner 214 and the composite casing 230 were bonded together along the length of the interface. If the composite casing 230 was formed on the metallic liner 214, the bonding was usually achieved by the epoxy or other resin used to bond the composite fibers. If the composite casing 230 was formed on a mandrel, or some other device, and then placed on the metallic barrel liner, the bonding was typically accomplished by coating the metallic liner with a bonding material.

As was discussed in the background section, the variation in bond strength due to uneven application between the metallic liner 214 and the composite casing 230 leads to uneven stresses during expansion and contraction due to both atmospheric changes, and the heat generated by repeated firing of the weapon. During the expansion and contraction of the metallic barrel liner 214 and the composite barrel casing 230, it is common for some of the bonding material to break free of the composite casing or the metallic liner.

When some, but not all of the bonding material breaks free of the casing 230 or the liner 214, portions of the casing and liner pull against one another, while other portions are able to freely move. This results in the barrel 210 warping under the differing stresses. The warping, in turn, decreases the accuracy of the gun and causes increased friction between the metallic barrel liner and a bullet passing therethrough.

In contrast to the prior art, the present invention does not bond the metallic liner 214 and the composite casing 230 together along the entire length of the barrel 210. In the embodiment shown in FIG. 6, no bonding agent is used along the entire length of the interface 234 between the composite casing 230 and

the metallic liner 214. In the alternative, the composite casing 230 and the metallic liner 214 can be freed from bonding together by use of a release agent such as TEFLON spray to provide a nonbonded interface 234 between the composite casing 230 and the metallic liner 214. Disposed along the second section 230b of the composite casing 230 and the second portion 214b of the metallic liner 214 is a holding pin 240 which extends into the metallic liner and the composite casing. The holding pin 240 is disposed in a position which prevents rotation of the composite casing 230 relative to the metallic liner 214. The holding pin 240 can be made of numerous different materials, but steel is believed to be a preferred material.

Also shown in FIG. 6 is a standard threaded barrel mounting 244 at an end of the second portion 214b of the metallic liner 214 opposite the first portion 214a. The threaded barrel mounting 244 allows the barrel to be mounted to a conventional machined metal action. A threaded tapered pre-stress insert 248 is also shown, the insert being disposed adjacent the open, first end 218 of the barrel 210. The pre-stress insert 248 is typically made of stainless steel, although those skilled in the art will be familiar with other materials which could be used. The pre-stress insert 248 stretches the barrel in advance of thermal expansion and thereby minimize the effects of the thermal expansion.

Referring now to FIG. 7, there is shown an alternate embodiment of the invention. Similar to the embodiment shown in FIG. 6, the embodiment shown in FIG. 7 has a barrel 310 having a metallic liner 314 and a composite casing 330 made of graphite or some other fibrous material as will be apparent to those skilled in the art.

The metallic liner has a first, thinner walled portion 314a near an open first end 318 of the barrel 310, and a second, thicker walled portion 314b, adjacent a second end 322 of the barrel. The second, thicker walled portion 314b forms a chamber 324 for receiving a cartridge 326. Unlike the embodiment shown in FIG. 6, however, the interface 334 between the metallic liner 314 and the composite casing 330 is bonded along a portion thereof. Disposed along the interface 334 between the second portion 314b of the metallic liner 314 and the

second section 330b of the composite casing 330 is a bonding layer 338. The bonding layer will typically be a layer of epoxy, but may be made of other bonding agents as well.

The bonding layer 338 holds the second section 330b of the composite casing 330 to the second portion 314b of the metallic liner 314 so as to prevent rotation of the casing relative to the liner, and to prevent the two from separating. The bonding layer 338, however, will typically be uniformly displaced around the barrel for a length of only two or three inches. Over such a length, the expansion and contraction of the composite casing 330 and the metallic liner 314 presents a lower risk of warping the barrel. At least a substantial portion of the remaining length of the interface 334 between the composite casing 330 and the metallic liner 314 is not bonded so as to allow the casing and the liner to expand and contract independently of one another.

Those skilled in the art will recognize that gun barrels could achieve some of the advantages of the present invention while using a bonding layer extending a greater length. For example, the bonding layer 338 could be half the length of the barrel 310, while still achieving some benefit by allowing the liner and casing of the remaining, nonbonded length of the barrel to move relative to one another. However, it is believed that having the bonding layer be no more than 4 inches on a traditional rifle barrel provides superior results.

While shown in FIG. 7 as being disposed at the second end 322 of the barrel 310, the bonding layer could be disposed at the first end 318 of the barrel, as is shown at 338b. In such a position, the heat from repeated firing of bullets would not effect the bonding layer 338 with as much intensity due to its remoteness from the point of firing. However, such a position of the bonding layer 338 leaves the second section 330b of the composite casing 330 and the second portion 314b of the metallic liner 314 unattached. This concern could be overcome by using a holding means such as a holding pin 340, or other similar device, to prevent rotation of the second section 330b of the casing 330 relative to the second portion 314b of the metallic liner 314.

As with the embodiment shown in FIG. 5, the embodiment of FIG. 7 includes a barrel mounting 344 at the second end 322 of the barrel 310, and a pre-stress insert 348 at the open first end 318.

Referring now to FIG. 8, there is shown a perspective view of a barrel, generally indicated at 410 being formed from a metallic barrel liner 414 overlaid with a composite material 430. The composite material 430 will preferentially be a strip of fiberglass mesh about 26 inches long, which is commonly referred to as fiberglass scrim cloth. The fiberglass scrim cloth 430 may be preimpregnated with a resin or epoxy, i.e. "prepreg", or may be coated with resin or epoxy shortly before being placed on the metallic liner 414. The epoxy or resin connects the fiberglass fibers 430a of the scrim cloth 430 to form a nonconductive composite isolator or insulative layer between the metallic liner 414 and the remainder of the composite casing.

The scrim cloth 430 is covered with graphite fibers 434 to create a composite casing (230 in FIG. 6 and 330 in FIG. 7). The initial graphite layer 434 will typically be graphite tape which is hoop wound, i.e. wound about the metallic liner 414 generally perpendicular to the long axis A-A of the liner. Of course, the tape 434 could be wound in a helical pattern, or a single strand or roving of graphite could be used and would be wound at approximately 1-5 degrees from peφendicular to the long axis. Additionally, other composite materials may be used. Those skilled in the art will be familiar with the different techniques for winding prepreg tape 434 or single or multiple roving of graphite fiber impregnated with resin at application, as well as other forms of composite winding which may be used with the present invention. Following the hoop wound layer 434, additional graphite fibers 434a are disposed along the metallic liner 414 in an axial or longitudinal direction generally parallel with the long axis of the metallic liner. After one or more layers (typically 5 to 15) of the axial fibers, another hoop wound layer 434b is applied. The process is then repeated for several alternating groups of hoop wound and axially placed layers. By controlling the number of hoop wound layers to the number of axially placed layers, the thermal expansion coefficient of the composite casing (230 in FIG. 6 and 230 in FIG. 7) can be controlled.

The higher the number of hoop layers, the lower the coefficient of thermal expansion in a radial direction. However, stiffness in the direction (resistance to bending the barrel) is improved with increased quantity of axial fibers.

As the resin or epoxy impregnated tape 434 is overlaid on the metallic liner 414, the lining is or can be coated with a release agent to prevent the resin or epoxy from bonding with the liner. Preferentially, however, a release agent 436 is coated on the metallic liner 414 to prevent the epoxy or resin from bonding to the liner, or the bond is broken by a controlled use of heat and pressure as opposed to the heat and pressure introduced during use. Once several alternating groups of hoop wound fibers and axially laid fibers are applied to the metallic liner 414, an overwrap 442 is placed about the composite/metallic gun barrel 410. The overwrap 442 can be a knitted or woven cloth, a camouflage or decorative cloth, plastic shrink tube, or a helical graphite/epoxy outer layer overwrap. The overwrap 442 helps to protect the fibers 430a and 430b, and allows an aesthetically pleasing finish to be formed on the outside of the gun barrel 410.

Referring now to FIG. 9, there is shown a perspective view of a composite portion 530 of a gun barrel being formed about a mandrel 535. Rather than using a graphite tape, such as that shown in FIG. 8, a single graphite thread 530a is wound about the fiberglass insulative layer 532 which is formed about the mandrel 535. This is typically accomplished by placing the mandrel 535 on a lathe (not shown) or similar machine, applying the fiberglass layer 532 and then rotating the mandrel at a high rate of speed. The resin or epoxy coated graphite forms a hoop wound layer. Longitudinal layers and additional hoop layers are applied to achieve a desired thickness.

Because the composite layer 530 will be removed after curing, a release layer 536 is typically applied to the mandrel 535 prior to applying the initial layer of fiberglass. Those skilled in the art will be familiar with such materials and their use. Once removed from the mandrel 535, the cured composite layer 530 and fiberglass 532 are slid over a metallic liner to form the barrel of a gun. Using a composite layer which has been cured on a mandrel 535 is advantageous in that

failure to properly coat the metallic liner with a release agent could result in the composite portion being attached at undesirable locations to the composite casing. This in turn may cause warping as discussed above.

This concern is overcome when using the mandrel 535, as the bond between the mandrel and the fiberglass layer of the composite casing must be broken to remove the mandrel. The mandrel 535 is also easier to work with, especially when applying a single graphite thread, and the risk of damaging the thin walls of the first portion (214a in FIG. 6 and 314a in FIG. 7) is not present.

An additional advantage of using the mandrel 535 is that it is substantially easier to apply a consistent, short bonding layer, such as bonding layer 338 in FIG. 7, when the composite casing is formed prior to being placed about the metallic liner. If the composite casing is formed on the liner, the maker must be careful that the release agent remains uniform and only on the areas along which the interface (234 in FIG. 1 and 234 in FIG. 2) between the casing and the liner are to remain nonbonded.

Thus, there is disclosed a composite/ metallic gun barrel in which the coefficients of thermal expansion and the attachment of the composite and metallic portion of the gun barrel are correlated to enable the tailoring of the gun barrel to the particular use characteristics desired for the gun. If a highly accurate rifle is desired, the gun barrel is formed in accordance with the first application of the teachings of the present invention. If a rapid fire gun is desired with resists premature wear, the second application of the principles of the present invention may be used. Of course the third application of the teachings of the present invention may be used with either of the first two, or independently to provide a composite/metallic gun barrel which is particular suited for its intended use.

In light of the above disclosure, those skilled in the art will recognize numerous modifications which can be made without departing from the scope and spirit of the present invention. The appended claims are intended to cover such modifications.