Bolt assembly for firearm
A modular two-piece bolt system for firearms with blowback actions provides a rear bolt piece which detachably couples to plural different front bolt pieces each of different mass. The front bolt pieces have a similar configuration and common coupling interface which forms an interlocked relationship with a complementary configured coupling interface on the rear bolt piece to prevent axial separation of the pieces when the action of the firearm is cycled. The system allows various front bolt pieces to be selected and used interchangeably with the rear bolt piece so that a front bolt piece of proper mass can be matched to the energy of ammunition to be fired. The front and rear bolt pieces when coupled define a continuous extended longitudinal passage which receives the rear breech end portion of the firearm barrel therethrough to reduce the projected length of the barrel.
1 . A modular bolt assembly system for a firearm with blowback operating system comprising:
a longitudinal axis;
a first front bolt piece having a first mass and internally comprising a first longitudinal passage coaxial with the longitudinal axis, the first longitudinal passage being configured to receive a rear portion of a first firearm barrel chambered for a first cartridge;
a second front bolt piece having a second mass different than the first mass, the second front bolt piece internally comprising a second longitudinal passage coaxial with the longitudinal axis, the second longitudinal passage being configured to receive a rear portion of a second firearm barrel chambered for a second cartridge having a propellant powder charge with energy different than the first cartridge;
a rear bolt piece internally comprising a third longitudinal passage coaxial with the longitudinal axis, the third longitudinal passage comprising a breech face and being configured to receive the rear portions of the first or second firearm barrel;
wherein the first and second front bolt pieces each have a common first coupling interface configured to mate with a corresponding complementary configured second coupling interface formed on the rear bolt piece;
wherein the rear bolt piece is detachably coupleable to the first or second front bolt piece to form a mechanical interlock which prevents separation thereof in a direction along the longitudinal axis.
2 . The system according to claim 1 , wherein the third longitudinal passage of the rear bolt piece is in communication with the first longitudinal passage or the second longitudinal passage depending on whether the first front bolt piece or the second front bolt piece is coupled to the rear bolt piece.
3 . The system according to claim 1 , wherein the first and second front bolt pieces each have a similar configuration.
4 . The system according to claim 3 , wherein the common first coupling interface of the first and second front bolt pieces comprises: (1) a male key which is insertable into a female keyway of the rear bolt piece; or (2) a female keyway which receives a male key of the rear bolt piece.
5 . The system according to claim 4 , wherein the male key comprises a U-shaped coupling protrusion and the female keyway comprises a complementary configured U-shaped coupling channel into which the coupling protrusion is slideably insertable.
6 . The system according to claim 5 , wherein the coupling protrusion is disposed on a front of the rear bolt piece and the coupling channel is disposed on a rear of the first and second front bolt pieces.
7 . The system according to claim 2 , wherein the first longitudinal passage extends completely through the first front bolt piece from end to end, and the second longitudinal passage extends completely through the second front bolt piece from end to end.
8 . The system according to claim 1 , wherein the rear bolt piece includes a firing pin.
9 . The system according to claim 1 , wherein the bolt assembly is configured so as to be non-rotatable in the receiver.
10 . The system according to claim 6 , wherein the coupling protrusion comprises a radially projecting flange which is integrally formed with the rear bolt piece as a unitary structural part thereof and insertable into the coupling channel of the rear bolt piece.
11 . The system according to claim 1 , further comprising a helical recoil spring mounted on a guide rod which is slideably receivable inside an axial guide rod passage formed in each of the first and second front bolt pieces.
12 . The system according to claim 11 , wherein the guide rod is projectible forward and rearward in the guide rod passage when the bolt assembly moves along the longitudinal axis between a rearward open breech position and a forward closed breech position when mounted in an axially elongated internal cavity of a receiver of the firearm.
13 . The system according to claim 12 , wherein the guide rod is fixedly attached to the receiver and remains stationary when the bolt assembly moves between the open breech position and the closed breech position.
14 . The system according to claim 13 , wherein the recoil spring acts on a rear end of the first or second front bolt piece when coupled to the bolt piece alone at a rear entrance to the guide rod passage to bias the entire bolt assembly forward to the forward closed breech position.
15 . The system according to claim 1 , wherein each of the first and second front bolt pieces and the rear bolt piece comprise a pair of linear bottom longitudinal support surfaces configured to slideably engage a bottom surface in an internal cavity of a receiver when the bolt assembly is mounted in the firearm.
16 . The system according to claim 1 , wherein each of the first and second front bolt pieces and the rear bolt piece has a substantially rectangular cuboid configuration.
17 . The system according to claim 4 , wherein the male key is insertable into the female keyway in a direction transverse to the longitudinal axis of the bolt assembly.
18 . The system according to claim 1 , wherein the first, second, and third longitudinal passages of the first front bolt piece, second front bolt piece, and rear bolt piece are formed internally in the first front bolt piece, second front bolt piece, and rear bolt piece, respectively.
19 . The system according to claim 1 , wherein the third longitudinal passage of the rear bolt piece extends partially rearward from a front end of the rear bolt piece to a point terminated by a vertical breech face inside the third longitudinal passage.
20 . The system according to claim 19 , wherein the breech face is configured to engage a rear breech end of a barrel of a firearm defining a chamber for an ammunition cartridge.