Gas piston retrofit for rifle

1. A gas piston retrofit assembly for a firearm having a bolt assembly mounted within a receiver, a barrel extending forward from the receiver, and a front sight block mounted on the barrel, said retrofit assembly comprising:

a gas tube extending into the front sight block fluidly connected with the barrel;

a piston cylinder having an arcuate-shaped piston chamber fluidly connected to the gas tube; and

a piston including an arcuate-shaped piston head extending forward from a piston body and telescopically received in the piston chamber, and including a piston rod extending rearward from the piston body and dimensioned and configured to extend into the receiver for engaging with a bolt assembly within the receiver,

wherein upon firing a round of ammunition, pressurized gas within the barrel enters the piston chamber to move the piston rearward, for cycling the bolt assembly,

wherein the gas tube is a hollow cylinder and a centerline of the gas tube is substantially parallel to a centerline of the piston cylinder, and

wherein the piston body includes an eccentric shoulder to abut a barrel nut to limit rearward motion of the piston rod into the receiver, and wherein the piston head includes a tapered portion to accommodate alignment of the piston head with the arcuate-shaped piston chamber.

2. A gas piston retrofit assembly for firearm according to claim 1 , wherein the piston cylinder includes an adjustable valve.

3. A gas piston retrofit for firearm according to claim 2 , wherein the adjustable valve includes a valve pin extending transversely through the piston cylinder.

4. A gas piston retrofit for firearm according to claim 3 , wherein the valve pin adjustable to throttle a gas line extending between the gas tube and the piston chamber.

5. A gas piston retrofit assembly for firearm according to claim 1 , wherein the piston body includes a rearward surface dimensioned and configured to abut against the stop ring to limit rearward motion of the piston rod into the receiver.

6. A gas piston retrofit assembly for firearm according to claim 1 , wherein the stop ring has a gap which can be turned upward to align the gap with the piston body thereby preventing abutting contact between the piston body and the stop ring to allow for disassembly of the retrofit assembly.

7. A gas piston retrofit assembly for firearm according to claim 1 , further comprising:

a stop ring dimensioned and configured for mounting on the barrel or piston rod and for limiting rearward motion of the piston body; and

a bushing through which the piston rod extends.

8. A gas piston retrofit assembly for firearm according to claim 1 , wherein the piston cylinder is arcuated to maximize a cross-section surface area of the arcuate-shaped piston chamber while providing a low profile gas piston retrofit assembly, and wherein the piston cylinder is fixed on the barrel rearward from the front sight block and the piston head is secured to the piston body by a locking pin such that the gas piston retrofit assembly can be releasably mounted onto firearms.

9. A method of retrofitting a firearm having a bolt assembly mounted within a receiver, a barrel extending forward from the receiver, and a front sight block mounted on the barrel, said method comprising:

providing a gas tube and a piston cylinder having an arcuate-shaped piston chamber fluidly connected to the gas tube, wherein the gas tube is a hollow cylinder and a centerline of the gas tube is substantially parallel to a centerline of the piston cylinder;

inserting an arcuate-shaped piston head of a piston into the piston chamber, the piston including a piston body and piston rod extending rearward from the piston head, the piston rod dimensioned and configured to extend into the receiver for engaging with a bolt assembly within the receiver; and

mounting a stop ring on the barrel, the stop ring being dimensioned and configured for limiting rearward motion of the piston body;

wherein the piston body includes an eccentric shoulder to abut a barrel nut to limit rearward motion of the piston rod into the receiver, and wherein the piston head includes a tapered portion to accommodate alignment of the piston head with the arcuate-shaped piston chamber; and

wherein upon firing a round of ammunition, pressurized gas within the barrel enters the piston chamber to move the piston rearward and cycle the bolt assembly.

10. A method of retrofitting a firearm according to claim 9 , wherein the method further comprises adjusting a valve pin extending transversely through the piston cylinder.

11. A method of retrofitting a firearm according to claim 10 , wherein the step of adjusting the valve pin throttles a gas line extending between the gas tube and the piston chamber.

12. A method of retrofitting a firearm according to claim 9 , wherein the piston body includes a rearward surface dimensioned and configured to abut against the stop ring to limit rearward motion of the piston rod into the receiver.

13. A method of retrofitting a firearm according to claim 9 , wherein the stop ring has a gap, the method further comprising turning the stop ring upward to align the gap with the piston body thereby preventing abutting contact between the piston body and the stop ring to allow for disassembly of the retrofit assembly.

14. A firearm having a bolt assembly mounted within a receiver, a barrel extending forward from the receiver, and a front sight block mounted on the barrel, the firearm further comprising:

a gas tube extending into the front sight block fluidly connected with the barrel;

a piston cylinder having an arcuate-shaped piston chamber fluidly connected to the gas tube;

a piston including an arcuate-shaped piston head extending forward from a piston body and telescopically received in the piston chamber, and including a piston rod extending rearward from the piston body and dimensioned and configured to extend into the receiver for engaging with a bolt assembly within the receiver;

a stop ring dimensioned and configured for mounting on the barrel and for limiting rearward motion of the piston body; and

a bushing through which the piston rod extends;

wherein the piston body includes an eccentric shoulder to abut a barrel nut to limit rearward motion of the piston rod. into the receiver, and wherein the piston head includes a tapered portion to accommodate alignment of the piston head with the arcuate-shaped piston chamber;

wherein the gas tube is a hollow cylinder and a centerline of the gas tube is substantially parallel to a centerline of the piston cylinder; and

wherein upon firing a round of ammunition, pressurized gas within the barrel enters the piston chamber to move the piston rearward, for cycling the bolt assembly.

15. A firearm according to claim 14 , wherein the piston cylinder includes an adjustable valve.

16. A firearm according to claim 15 , wherein the adjustable valve includes a valve pin extending transversely through the piston cylinder.

17. A firearm according to claim 16 , wherein the valve pin is adjustable to throttle a gas line extending between the gas tube and the piston chamber.

18. A firearm according to claim 14 , wherein the piston body includes a rearward surface dimensioned and configured to abut against the stop ring to limit rearward motion of the piston rod into the receiver.

19. A firearm according to claim 14 , wherein the stop ring has a gap which can be turned upward to align the gap with the piston body thereby preventing abutting contact between the piston body and the stop ring to allow for disassembly of the retrofit assembly.