What velocity from a 392 should I expect?

What velocity from a 392 should I expect?

Joined: February 1st, 2008, 4:11 pm

May 7th, 2013, 4:48 am #1

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?

Thanks,
Erik
Quote
Share

Joined: March 28th, 2002, 6:54 pm

May 8th, 2013, 4:41 am #2

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.
Quote
Share

Joined: February 1st, 2008, 4:11 pm

May 8th, 2013, 5:20 pm #3

I have tried to read as much as I can about the mods you and Steve have posted. I will check to see if my pump arm does spring after six pumps, but my guess is the head space.
I ordered a new brass valve from crosman thinking the aluminum valve might be the culprit and am waiting for it to arrive. I did make a HDD and try the check valve mod, but that didn't change velocity. The gun is brand new and seems to be working properly with no leaks or blow by.
My valve is stable and not moving. Would adding the larger o ring to the two valve halves be enough to reduce the head space? Do you have a link or recommendation on the best way to reduce the headspace? Thanks for your suggestions and response to my post.

Erik
Quote
Share

Joined: March 28th, 2002, 6:54 pm

May 9th, 2013, 2:59 am #4

and he's even come up with a way to figure out how much of a turn for a given amount of headspace..but I'm afraid I didn't save a link. If you ask there, someone else may have it.
Quote
Share

Joined: May 12th, 2001, 1:29 pm

May 20th, 2013, 4:12 pm #5

Quote
Share