The invention relates to firearms, especially, though not exclusively, firearms for use by security forces for dispersing rioters and the Like.

It is known to provide 'riot-nun' firearms to fire one of a number of different types of ammunition such as large- or small- calibre flare rounds, baton-rounds, ηas cartridges and live ammunition such as shotgun rounds.

Unfortunately this has required the utilisation of a large number of firearms, and it is impracticable for a user to have to carry several firearms to suit different calibres ^" or types of a munition.

The invention provides a firearm adapted to selectively fire ammunition o two or more different calibres, the firearm comprising a gun body incorporating a firing mechanism, at least two interchangeable barrels, the gun-body having means for selectively receiving one of said at least two interchange-, able barrels in a releasably securable manner, and means for releasably securing, in at least one of said barrels, a barrel- insert permitting the use of ammunition of a smaller calibre than the barrel in which the barrel-insert can be received.

Preferably the gun body comprises a main part, which inc¬ orporates a firing mechanism, and a breech part which is pivo- tally mounted on the main part. Alternatively the breech part is releasably mounted on the main part..

Preferably also the barrel receiving means of the qun body

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comprises α screw threaded arrangement arranged to co-operate with a screw threaded arrangement of each of the barrels. Alternatively the barrel receiving means of the gun body comp¬ rises a snap fit arrangement adapted to co-operate with paϊts of each of the barrels.

The insert receiving means may comprise a recess in said at least one barrel for receiving a ^f longed end of the insert, whereby the latter can be clomped between the barrel and the main part of the gun body.

I" another arrangement the insert receiving means may comprise a recess in the breech part for receiving a flanged end o^ an insert arrangement, whereby the latter can be clamped between the breech part and the main part of the gun body.

The insert arrangement may comprise o πerπber within which the insert is mounted and which is adapted to space the insert from the barrel, the flanqed end being provided in the spacing member.

Desirably means are provided on the gun body for ejecting spent cartridge cases, the ejecting means being adapted to co¬ operate either directly with the coses or indirectly with the cases by means of auxiliary ejecting means associated with the insert.

Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which :-

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Fin. 1 is α schematic side elevational view of a firearm according to the invention, fitted with a large-calibre barrel, certain parts being shown in cross-section;

Figs. 2a and ?b are schematic side elevational views of a front part of the firearm similar to that shown in Fig. 1, having - fitted thereto a small-calibre barrel-insert inside the large-calibre barrel;

Fig. 3 is a cross-sectional view of a part of the firearm o Fig. 1, having fitted thereto a short large-calibre barrel with a small-calibre barrel insert therein; and

Fig. A is a cross-sectional view of a part of the firearm shown in Fig. 1 , showing an alternative barrel mounting.

Fig. 1 shows a firearm having a gun body 10 having a soc¬ ket at a rear part for receiving a stock 12 and having a pistol grip 14. A breech block ^6 is mounted on the gun-body 10 by means of a pivot 18, the breech block being secured to the gun- body for firing by a catch 20.

The gun-body 10 has a firing mechanism (only part of which is shown) including a firing pin 22, a part 24 of which is pro¬ vided with an aperture 26. The latter can receive a locking pin 28 which is depressed against the urging of a spring 30, unless the catch 20 is properly engaged with the breech block 16. The firearm is thus prevented from firing unless the breech block is in proper engagement with the gun body 10. The breech block- 16 receives the breech end of a barrel 32 in a sliding fit within a socket, the barrel being locked in place by a series of ball catches 34. These comprise a series of

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eight circu ferentiαlly-spαced ball bearings 36 which, in the locked position, have lower portions which can protrude into a circumferential groove provided on the outside of the barrel socket. The ball bearings 36 are held in this position by a sleeve 38 urged into a locked position by a spring 39. When slid aside against the spring 3° the sleeve 38 allows the ball bearings 36 to retract from the socket allowing the barrel 32 to be withdrawn.

The breech block lό also incorporates a cartridge ejector mechanism comprising an ejector slide 40 having an abutment 40a which, when the breech is pivoted open, abuts a stop 42, on the gun body 10. The latter, as the breech is opened more, pushes the ejector slide 40 rearwσrdly relative to the breech block so that an abutment 40b ejects the rim of a cartridge 46. The barrel 32 shown in Fig. 1 is a 38 mm-cσlibre long barrel suit¬ able for firing a baton-round (for example of rubber or plast¬ ics) or a gas-round. A short barrel 70 as shown in Fig. 3 and as described in more detail hereinafter can be fitted instead of the bnn barrel so that the weapon can be used as a pistol. The short barrel can be used for firing 38 m -calibre flare rounds, or gas or baton-rounds, where accuracy is not required, or in an emergency.

Figs. ?σ and 2b show a firearm similar in most respects to that shown in Fig. 1 { and similar reference numerals have been used for corresponding parts), except that a barrel 50 ^" is screw threaded into the breech block 16, and the firearm is shown with a small (12 gauge) calibre barrel insert 58 within

the 38 mm-cαlibre barrel 50. Fig. 2a shows the rear part of the barrel 50, and Fig. 2b the front part.

The large calibre barrel 50 is attached to the breech block 16 by means of an external screw threaded section 52 and is prevented from unscrewing by means of a locking screw 54 which is tightened on to an outer surface of the barrel socket. A barrel-insert assembly is received within the barrel 50 and comprises a rear spacing block 56 into which is threadingly enqaqed the barrel insert 58. A forward spacing block 60 (see Fig. 2b) spaces the small-calibre barrel insert 58 within the barrel 50 at a front end of the latter. The cartridge ejector slide 40 instead of acting on the rim of a cartridge, acts on an abutment of a secondary ejector 62 which is part of the spacing block 56 and which acts on the rim of a cartridge in the small-calibre barrel insert 58 to eject the cartridge case.

Fig. 3 shows part of the breech block 16 of the firearm of Fig. 1 incorporating the short barrel 70 ~s an alternative to the long 38 mm-calibre barrel 32. ^' There is also shown a small V-calibre barrel insert 72 (for firing small baton or flare rounds) retained in the barrel 70 by means of a flange 74 corresponding to the rim of a large-calibre cartridge. A secondary ejector 76 is provided which is operated.by an ejector slide 78 of the large-diameter barrel 70 in a manner the same as that described in relation to the firearm shown in Fig. 2a.

Fig. 4 shows an alternative type of screw thread arrange¬ ment for securing a barrel 80 to a breech block 82, by means

of an ' acme' thread 84.

It is to be understood that various modifications may be made without departing from the invention. For example, any convenient fixing of a barrel in the breech block may be emp¬ loyed, the examples shown being the screw-thread and snap-fit arrangements. A permanent barrel may be provided on a breech block within which barrel inserts of other calibres may be received by any suitable means in addition to those descr¬ ibed, the breech block being rapidly interchangeable with another breech block having a permanent or detachable barrel. The breech block may be secured for example by a releasable pivot pin.

The firearm may be made from any suitable material such as alloy, pure metal, and where appropriate, plastics. Where a lonq barrel is fitted, an additional hand-grip may be fitted about half way along the barrel. The hand-griρ(s) and/or stock may be provided with rings to accommodate a sling.

The barrel or any of the barrels may be rifled where appropriate. Each barrel or barrel insert (when fitted) may be used to fire any appropriate ammunition. For example the 12-πauge barrel may be used to fire a gas, buckshot, or slug- round (for example to kill escaped dangerous animals).

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