Restoration of Crosman V-350 BB Gun

[GBertolet]

I rediscovered this BB gun, I had from the mid 1960's. I hadn't fired it in years. Chronographed it @ 205 fps, while an occasional BB dribbles out of the barrel. Quite low, supposedly should be in the 350 fps range. I purchased a seal rebuild kit along with mainspring. Still 205 fps. Something is wrong here. I made up a test plunger to test compression in the tube. There is none. I don't feel any air coming out the barrel either, but there is vacuum when withdrawing the plunger. I don't get it. Where is the air going? There is some sort of pop off valve barrel cap, threaded to the rear of the barrel. Maybe this has something to do with it.

Can anyone have experience with this BB gun that can give me some guidance?

[Multigunner]

The Crosman M1 Carbine is based on the V350 action. There is a pop off valve that doubles as a probe to push the BBs past a retaining spring. If its not moving all the way forwards the BBs may hang up on the spring or some air pressure be bled off through the opening to the magazine before the BBs start to move.

Everything must be clean and move freely to work well. A weak mainspring could also be the culprit.

[n.h.schmidt]

Hi
I used to have a Sears version of this BB gun. It was at least average powered and I could hit stuff. Sadly I treated it badly and it is gone. I Hope you will let us know the FPS when you get it working better. I think 350 FPS is way higher than what it will do. Most BB guns claimed to get 350FPS actually get more like 285 to 300 FPS. I have tested The new Daisy 25 and a old 25 from 1936. The new one got 285 and the old one 300. Claims of up to 400FPS with older 25s seem to be unrealistic.
n.h.schmidt

[GBertolet]

Multigunner, I never really understood the functioning of the pop off valve, so your explanation sheds some light on what might be happening with that part. I had recently put in a new spring and seals, and those made no difference.