Background of the Invention Self-loading firearms includes semi-automatic or automatic firearms. For self-loading firearms operating on the pure blowback system, the barrel is fixed to the frame of the firearm and the breechblock moves reciprocally from the forward battery position to the rearmost position on the frame of the firearm to extract the empty cartridge from the firing chamber that resulted from firing a round of ammunition. The breechblock ejects the cartridge from the firearm and simultaneously cocks the hammer. Another round of the cartridge is picked up from the magazine when the breechblock moves forwards towards the battery position to close the breech opening and loads the cartridge into the firing chamber.

When firing pin strikes the primer of the cartridge, the gas pressure resulting from the explosion is at its greatest during the initial explosion and exerts a force on the bullet to propel the bullet out of the barrel and also exerts a reactive force on the cartridge case and the breechblock, thus pushing the breechblock rearwards and extracting the empty cartridge case. The extraction of the empty cartridge can occur during the high pressure, especially if the breechblock is light and some of the gas escapes through the open breech. The gas pressure within the barrel is thus reduced and less force is available to propel the bullet out of the barrel, yielding low bullet velocity and hence poor penetration power when the bullet

impacts the target. Also, if the breechblock is too light, the breech may open too early and the cartridge case may rupture.

This can cause jamming of the firearm and may cause injury to the user. The firearm therefore has to be limited to low to medium powered ammunition. Further more, a moment is created about the wrist that tends to rotate the gun barrel upward after firing which can be undesirable especially for automatic firearm. Ammunitions are wasted in such firing and the user has to frequently change reload the firearm. Hence it is desirable to provide firearms with a delayed breech opening mechanism which causes the bullet to be propelled with higher velocity, allows the usage of higher powered ammunition, reduces the upward movement of the barrel after each firing and also reduces the firing cyclic rate.

One means of delaying the opening of the breech is to increase the mass of the breechblock. The mass of breechblock and the recoil forms an inbuilt delaying mechanism whereby the inertial force has to be overcome first before the recoil of the breechblock can start to initiate. For heavier powered ammunition, the heavier breechblock can be used to increase the necessary the delay but there is a limit weight of the breechblock because it becomes impractical for the firearm to become too heavy. Plus, a heavy breechblock can impair accuracy.

Another means of delaying the breech opening is discussed in US 4,232, 583. The firearm is provided with a roller that is movably held in a pair of spaced apart opposed inclined grooves formed in the upper rear portion of the weapon's frame. When the hammer strikes the primer, a cam surface provided on the hammer drives the roller is upwards until the roller is in contact with an inclined surface provided on the rear portion of

the breechblock. When the breechblock commence the recoil movement, the inclined surface exerts a force on the roller and drives it downwardly along the cam surface of the hammer and the breechblock can only resume the recoil movement when the roller is moved out of the recoil path. The roller for this patent is dependent on the hammer to wedge the roller against the breechblock. At this position, the roller is exposed to sand or dust that may be accumulated during utilization of the firearm or exposed to the residues that resulted from the explosion of the bullet. These particles do not only hamper the recoil movement of the breechblock, they also reduces the performance of the roller. Both the ends of the roller that are enclosed within the inclined groove may not simultaneously move upwards or downwards, hence, reducing the efficiency of the delay mechanism.

Another means of delaying the breech opening is adding a delaying mechanism to the breechblock. One delaying mechanism utilised in the model G3 manufactured by Heckler and Koch consists of two rollers mounted on either side of the breechblock and a firing pin fit between the rollers. When the breechblock is closed, the rollers act on the camming surfaces of the firing pin, wedging the rollers in the receiver frame.

When a bullet is fired, the breechblock is prevented from opening immediately. The firing pin must be forced rearwards first, allowing the rollers to disengage with the receiver frame before the breechblock can move rearwards. Here again, the rollers are exposed to dust particles and residues from the explosion.

In both these delaying means, there is no means provided to adjust amount breech opening delay when different ammunition size is used or to adjust firing rate with the same ammunition

size. Also, the delaying means provided for the existing firearms do not reduce the upward movement of the barrel after firing. The object of the invention is to provide a breech opening delaying means for a self-loading firearm operating on a blowback principle that is adjustable and simple to operate. A further object of the invention is to provide a means of reducing the upward movement of the barrel after each firing.

Summary of the Invention The self-loading firearm operating on the blowback principle of the current invention is provided with a delay mechanism that is located at the top front portion of the barrel. The delay mechanism comprises of a roller means biased reciprocally into and out of the movement path of the recoiling breechblock. The breechblock is provided with an inclined surface to form a recess in which the roller means is received, said roller means biasing against the inclined surface. The roller means is provided on the housing and is a spring is used to bias the roller means into the recess on the breechblock and against the inclined surface on the recess. The biasing of said roller means from said spring can be reversibly increased or decreased.

Brief Description of the Drawings The present invention may be more readily described by reference to the accompanying drawings in which: Figure 1 shows the side view of a self-reloading firearm showing the delaying mechanism of the breechblock.

Figure 2 shows the detailed structure of the breechblock.

Figure 3 shows the isometric view of the roller means and the recess on the breechblock.

Detailed Description of the Invention The terms"front","rear","forward","rearward","upper" and"lower"are used herein refer to any firearm when held in the normal firing position. The term"clockwise"used herein refers to the direction of rotation as shown in the respective figure. It should be noted that the details of some illustrated parts of the firearm do not play a role in the delay mechanism of the breechblock and therefore is not discussed here. Also, the invention is not limited to the illustration shown here. It will be understood that firearm is typical of a great variety of such weapons all of which operate in accordance with the same basic operating principles but different as to the structural details from one model to another and from one manufacturer to another. Therefore, the particular firearm as illustrated in Figure 1 is not to be construed as a limitation of the present invention in that the recoil movement delaying mechanism can be employed on all weapons that operate in accordance with the same basic principles.

Referring to Figure 1, essentially, a self-loading firearm comprises a housing (1) having a handgrip (5) adapted to be grasped by the user and in which the magazine (7) can be removably mounted, a barrel (17), a cartridge chamber on the rear end of the barrel, a trigger (3), a hammer (9), a firing pin (13), a trigger mechanism coupled to the trigger (3) and hammer (9) to cause the hammer (9) to strike the firing pin (13) thereby causing the firing pin (13) to engage with the primer of the bullet to discharge the firearm, recoil spring (11), and a breechblock member (15) as is customary.

The breechblock member (15) is slidably mounted within the housing (1) for reciprocal movement along the frame between the battery position and the rearmost position. The alternating movement between the battery position and the rearmost position defines the movement path of the breechblock (15). The detail of the breechblock (15) for the particular firearm illustrated in Figure 1 is shown in Figure 2.

The upper surface of the breechblock (15) is provided with a recess (19) with an inclining surface (20) (see Figure 3).

When the breechblock (15) is in the battery position as shown in Figure 1, the recess receives a roller (21) that is provided on the breechblock cover (la) and is downwardly biased to be reciprocally movable into and out of the movement path of the breechblock (15). When the roller (21) is received in the recess (19), the roller (21) is said to be in the movement path of the breechblock (15) and provides a downwardly force which impedes and delays the rearward movement of the breechblock (15). The roller is also forwardly biased such that when it is received in the recess (19), apart from exerting a force downwardly, the roller (21) will also exert a forward force against the inclined surface (20) of the recess (19) to increase the impediment to the rearward movement of the breechblock (15).

One way of biasing the roller means into and out of the movement path of the breechblock is to use a coil spring. The coil spring is placed through a perforation provided from the top of the breechblock cover (la) that extends downwardly from the top the breechblock (15) and inclined in the opposite direction of the inclined surface (20). The lower end of the inclined coil spring is provided with a means of attaching to the roller (21). The upper end of the coil spring is fixed within the breechblock cover (la) with a threaded cap. Another

way of biasing the roller means (21) into and out of the movement path of the breechblock (15) is to use a torsion spring.

However, the preferred means of biasing the roller (21) is illustrated in Figure 1. A lever (23) is attached on its front end to the housing via a pivot pin (25) and the rear end of the lever (23) is provided with a roller (21) that is pivoted to the rear end with a pivot pin (22). Preferably, the rear end is provided with two arms that extend rearwardly to receive the roller (21) in between the arms and a pivot pin (22) is used to secure the roller (21) to the arms. The front end of the lever (23) is provided with an arm (27) that extends upwardly from the pivotal point (25) of the lever (23) and the breechblock cover (la) and is biased rearwards.

A coil spring (31) is mounted onto a pin (33) of a cap (29). The front end of the breechblock cover (la) is provided with a horizontal bore (37) into which the coil spring (31) is introduced. The coil spring (31) is maintained within the bore (37) and is compressed by a threaded cap (35). The rear end of the coil spring (31) with the cap (29) biases against the front surface of the lever arm (27) to push the lever arm (27) rearwards and rotates roller (21) on the lever (23) clock-wise, biasing the roller (21) downwardly and forwardly. The threaded cap (35) is reversibly adjustable by screwing in or out of the bore (37) to increase or decrease the biasing on the roller (21), which therefore makes it adjustable to increase or decrease the impediment of the breechblock (15) movement, and hence increase or decrease the amount of delay of the opening of the breech.

When the breechblock (15) is in the battery position, the roller (21) is biased into the movement path by being received in the recess (19) on the breechblock (15). When firing pin (13) is moved forward to strike the primer to drive the bullet out of the barrel (17), the gas from the explosion will push the bullet along and out of the barrel (17), and in the mean time will exert a reactive force on the cartridge case and thus the entire breechblock (15) to open the breech. Due to the roller (21) acting on the inclined surface (20), the breechblock (15) does not move rearwards immediately. The upward movement of the barrel is also reduced due to the force exerted by the spring (31) on the roller (21). When the roller is cammed out of the inclined surface (20), the lever arm (27) is pushed against the spring (31) and the compressed spring (31) will urge the roller into the recess (19) when the breechblock (15) returns to battery position. The delay mechanism is operable with the inclined angle ranging from 30° to 45°. The operable ratio of the depth of the recess (19) to the radius of the roller (21) is 2: 5 - 5 : 8. The delay mechanism operates optimally when the angle of the inclined surface (20) is 40°.

While the firearm illustrated in Figure 1 shows only one delay mechanism, the firearm is not limited to have only one such delay mechanism. The firearm can be provided with two of such delay mechanisms, whereby both the breechblock arm (15a, 15b) are provided with a recess on each arm to receive a roller.

It should be noted that the delay mechanism described here and illustrated in Figure 1 allows the delay mechanism to be placed at the top portion of the firearm's muzzle which spreads the weight towards the front of the firearm to reduce the upward movement of the muzzle during recoil. However, the delay mechanism is not limited to be provided only in that area.

It will be understood that the above description does not limit the invention to the above-given details. It is contemplated that various modifications and substitutions can be made without departing from the spirit and scope of the following claims.