Just got my first air pistol ever, crosman 1377. Used to big guns.
Anyway, I flattened the valve and got a brass flat top piston. The
velocity went from 470 fps with 7.9 grain pellet to 565 with 10 pumps. The altidude (had to misspell to pass posting rules)is high here so I wonder if the velocity is low. Does this valve diesel if oil gets into it? I oiled everything before I put it back together. Are you supposed to use fewer pumps? I also pumped it to 14 and got 615, and 15 to get 618. There's a slight amount of air left but not enough to spit out a pellet. After about 20 shots I suppose there is no dieseling, but are there any comments?

A stock valve, have you checked 4, 6 and 8 pumps for velocity?

P.S

We have the altitude issue worked out, seems the bad word checker disliked the middle of the word altitude.



Aww the cost of cleanliness

stock valve. Having to grip the breech and barrel to pump makes for irratic accuracy. The sight won't go low enough so it appears to be sighted in for 30 yards...I would rather it be set for 15. I graphed 3,5,10,12,14,15 pumps. Then drew an arc so you can predict velocities at other pumps. The points I had fell cleanly into the arc. I didn't want to spend much money on this, but the breech is lousy. I'm making Zebrawood grips for it. It's what I had laying around. I make guitars for a living.