392 8 or 10 pumps?

[Stonechucker]

What do you think guys? Will 10 pumps ruin my circa 2007 392PA.  How many more fps can I expect with the 2 extra pumps? One of these days I will by a chronograph, but every time I get the money together I have a real hard time not buying a gun😁

[bantam5s]

Probably not, but you probably won't gain much at all.

Do you always pump the thing 8 times every time you shoot it ?
I rarely ever pump any of my 13 or so pumpers more than 5 times, and usually just use 3-4.

[Stonechucker]

For hunting I do 8  all the time, but lately I did a test, and found my accuracy to be better with the jsb heavies if I go with a full 8 pumps during target shooting. I would normally only do 5 for targets or plinking in most cases however.

[Habanero69er]

So you're having to pumping to 10 to improve accuracy? Seems your barrel might be flexing due to the higher tube pressure, changing POI?  Doubt 8-10 pumps will hurt the rifle. Just keep the rifle's pivot points & cup lubed.
You'll definitely get a good arms/chest workout.   

[Stonechucker]

I don't do 10 pumps now, just asking if 10 will do harm.  I would only do 10 for hunting if there was a moderate fps advantage. I did observe in accuracy testing that I was able to get better groups with 8 pumps as opposed to 5 pumps with the JSB Heavies.  I don't know the reason. Could flight time have something to do with that?

[Hoosier Daddy]

While the gun is designed to be pumped 10 times...
You might try pumping it up 10, shoot, then re-cock and dry fire.
Did you get any air the second shot?
 If so it is not dumping all the air that was compressed in 10 pumps so there wont be any benefit to the added stress.

[Mole2017]

The chronograph would be handy for you right now. Hoosier Daddy's suggestion is good. I did similar while testing a rebuild I did for a 317. I measured the speed of several shots at 3, 4, 5, and more pump strokes. It was not emptying itself completely after a shot with 5 pumps and the subsequent shots were getting faster and faster, to a limit. Even the those subsequent 5 stroke in on the pump got harder and harder.

Then I did a round of testing where I pumped, say 6 strokes, took a shot and then reloaded and took another shot. It was soon apparent that even 5 or 6 pumps left enough air for a second shot, though at reduced velocity. Off the top of my head, this gun at 8 pumps had the equivalent of three or four pump strokes in retained air after a shot.

That leads to the final property of these guns that many take advantage of: A shot after 7 pumps, for example, leaves enough air in the gun so that 3 or 4 strokes gets you another shot of the same power. Then 3 or 4 strokes again for the next shot, and so on. Some retain more air than others and you can tune it some to control that.

The chrony will tell all.

Oh, and start low. Don't go for the max right off. In addition to being a lot of work, there is the possibility of valve lock with some guns: the pressure is so high that the hammer can pop the valve open for the shot.

[Stonechucker]

So I did 5 pumps then dry fired with 0 air, at 8 pumps there was some air left over but not enough to push a pellet through a cardboard box at 10 yards. Then did 10 pumps fired, then cocked the gun and shot without pumping this time the pellet barely made it through the box. My conclusion. I really need a chronograph.😁