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What velocity from a 392 should I expect?

May 7 2013 at 12:48 AM
Erik  (Login hegshen)
YF12

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

 
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scot laughlin
(Login classicalgas)
YF

Go to the crosman forum, and search 392..lots of easy tuneups for that gun

May 8 2013, 12:41 AM 

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.

 
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Erik
(Login hegshen)
YF12

Thanks for the suggestions Scot....

May 8 2013, 1:20 PM 

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

 
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scot laughlin
(Login classicalgas)
YF

Steve's valve unscrew mod is documented on the crosman forum somewhere

May 8 2013, 10:59 PM 

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.


    
This message has been edited by classicalgas on May 21, 2013 3:37 PM


 
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Steve in NC
(Login pneuguy)
AR&P

Right you are, Scot. Here's the link. The headspace reduction mod'...

May 20 2013, 12:12 PM 


 
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