Upon recoil of the barrel and rigidly attached rod 1 and piston 2 to the right, fluid from working end A flows through groove a on the inner surface of cylinder 3 into idle end B. This brakes the recoil. At this, a vacuum is set up in end B because the volume freed by the piston in end B is greater than the volume of fluid forced out of end A. During counterrecoil, after filling the vacuum, fluid is forced through groove a from end B to end A, braking the counterrecoil. At this, piston 2advances onto needle member 4, secured to the cylinder, forcing out the fluid inside the recess of the piston through the clearance. This also brakes counterrecoil.
$3773$SHP,FD$