3-cycle 2-stroke damper

1. An arm comprising:

a frame;

a trigger that is depressible to fire the arm once per operating cycle;

a gun bolt that is movable rearward and forward with respect to the frame;

a surface supported to the frame;

a piston supported to one of the gun bolt and the surface;

a cylinder that: 1) defines a cylinder bore; 2) has cylinder fluid within the cylinder bore; and, 3) is supported to the other of the gun bolt and the surface; and,

a biasing device that biases the gun bolt forward;

wherein on firing the arm, the arm is operable to:

1) move the gun bolt rearward to cause the piston to move with respect to the cylinder to: (a) compress the cylinder fluid within the cylinder bore to dampen rearward gun bolt speed; and then (b) move the cylinder with respect to the other of the gun bolt and the surface to create a vent that communicates the cylinder bore to an exterior of the cylinder bore; and then (c) force cylinder fluid to exit through the vent to the exterior of the cylinder bore; and

2) move the gun bolt forward to cause the piston to move with respect to the cylinder to reduce the pressure of cylinder fluid within the cylinder bore to dampen forward gun bolt speed.

2. The arm of claim 1 wherein:

the biasing device exerts a biasing force to hold the cylinder to the other of the gun bolt and the surface; and

moving the cylinder with respect to the other of the gun bolt and the surface overcomes the biasing force.

3. The arm of claim 1 wherein the biasing device:

exerts a biasing force to hold the piston to the one of the gun bolt and the surface; and

exerts a biasing force to hold the cylinder to the other of the gun bolt and the surface.

4. The arm of claim 1 wherein as the gun bolt reaches an end of a rearward stroke:

the cylinder moves with respect to the other of the gun bolt and the surface to close the vent.

5. The arm of claim 1 wherein:

the surface lies on a bolt stop;

the piston is supported to the gun bolt;

the cylinder is supported to the bolt stop;

the bolt stop has a gun bolt contact surface; and

when the gun bolt reaches an end of a rearward stroke: the gun bolt contacts the gun bolt contact surface of the bolt stop.

6. The arm of claim 1 wherein:

when the gun bolt moves rearward and the piston moves with respect to the cylinder to compress cylinder fluid within the cylinder bore: cylinder fluid pressure rises above atmospheric pressure; and

when the gun bolt moves forward and the piston moves with respect to the cylinder to reduce the pressure of cylinder fluid within the cylinder bore: cylinder fluid pressure falls below atmospheric pressure.

7. The arm of claim 1 wherein the arm is operable after moving the gun bolt forward to cause the piston to move with respect to the cylinder to reduce the pressure of cylinder fluid within the cylinder bore to dampen forward gun bolt speed to:

move the piston out of contact with the cylinder bore to stop dampening forward gun bolt speed.

8. The arm of claim 1 wherein:

the biasing device is a compression spring having a first end that contacts the gun bolt and a second end that contacts the surface.

9. The arm of claim 1 wherein:

the biasing device is a compression spring having a perimeter;

at least a portion of the piston is positioned inside the spring perimeter; and

at least a portion of the cylinder is positioned inside the spring perimeter.

10. The arm of claim 1 wherein:

the other of the gun bolt and the surface comprises a port;

the cylinder is supported to the other of the gun bolt and the surface with the port communicating with the cylinder bore; and

the arm is operable to move the gun bolt rearward to cause the piston to move with respect to the cylinder to: force cylinder fluid to exit through the port to an exterior of the cylinder bore.