Just bought a 392 and am getting about 543fps with 14.3g crosman pellets with the 8 pumps.I don't expect the 685fps, but I saw paul Capello's review and he was getting around 650 with 10 pumps.
I called crosman and the customer service rep todo me those were expected numbers. I am a bit disappointed, as I expected the gun to be shooting atleast over 600fps.
I did find out that they are now making the brass valves again instead of aluminum, so I ordered a brass valve. Perhaps this will make a difference, but I doubt it. I had expectations that the gun would shoot harder than 11 ft/lbs.
kinda wish I took my chances with the .22 rebel instead. Thoughts?
It's likely that you got a gun where the pump head to valve body clearance got big, due to tolerance stacking in the various parts,and increased head space to the point you are losing significant pump pressure.
Does the pump arm want to spring pretty far, or almost all the way open after about the sixth pump, once you've popped it loose from the tube? There are a couple fixes for this,it's a strong indication of excessive head space.
Is the take down socket bolt(which also holds the valve in place) loose enough to allow the valve to move in the tube? Do you lube the pump head and pivots regularly?
A happy 392 with snug head space will drive a 14.3 pellet at very close to 600 fps on eight pumps..some a little more, generally not less.