Anyone had this happen with a PCP ?

[Wolfdog91]

Recently had to replace the fill nipple on my Benjamin Maximus. Was shooting fine velocity stable and grouping wonderfully before but after the replacement Velocity average was spiking event other fill . Like first fill would average 790 for the first 20 shots then second fill would be 770 for 20 then like 780 on the third fill. And it kept going like that . Would fill with the samp pump to the same pressure same pellets and all. Well the other day I shot all the air out took the he gun apart for the most part , really just removed the air tube from the barrel ,took apart the trigger group , took the barrel off along with the reciver and top the hammer spring and hammer out the back.only thing I did was while some of the parts off on my shirt and threw it all back together. Seemed like all the deals I could see where fine. Well put it back together tighted every thing now with the same pellets and pump it's averaging around 795 every fill and it's grouping like it was when I first got it. Could re doing all the screws really make that much of a difference or could something else be going on ?

[georgerkahn]

Wolfdog91, I got bitten by the PCP bug but maybe three years ago, and now have five of these! Three are Crosman/Benjamins. I bought/installed a "goodie" called a de-pinger for my Maruder pistols, and on one -- the Woods Walker -- noted a similar unwelcome change in velocities. (I have/use a FX chrono which hangs from barrel as one shoots) Panicking just a little -- I reckoned I threw away any warranty on a costly airgun if I did something to mess it up. So, with trembling hands I took it apart, doing NOTHING MORE than observing; and, reassembled. I took it to camp that afternoon, and all discrepancies ceased!
I "know" I did absolutely nothing! BUT, I must have??? My thought -- no more -- is re the kind of sticky lub or coating on inside of tube? Again, I have zero idea what I did or didn't do... BUT, quite happy it is "fixed". (BTW, mine are in .22; I was using JSB Diabolo Exact pellets; pressured to 2,400psi; median muzzle velocity at 827fps)
geo

OOPS! I just noted a "typo" -- my median velocity was/is 827fps -- sorry -- I don't know how I hit a "4" ("847fps"), and didn't note my error, instead of the intended "2". Sorry.
geo

[rsterne]

Most likely there was some grit or thick lube on the hammer, causing inconsistent velocities.... and when you took it apart you fixed that problem....

Bob

[HollowPoint]

I've never had such a problem with my PCP but with my Break Barrel air rifles I have had problems suddenly develop out of the blue. And just like you did with your PCP, I'd take them apart looking to find the sources of the problem, only to find that nothing seemed to be wrong with any of the components.

When I put them back together, most of the time the darn things started working fine again. The few times when they still exhibited the problems that lead me to take them apart in the first place, it turned out to be something really simple to fix. So simple in fact that, it's simplicity is what caused me to miss it while I had the gun apart.

In my case with those break barrel problems it turned out to be a bad seal that to the naked eye appeared to be fine. The inconsistent velocities on your PCP would most likely be an inconsistent hammer strike just like rsterne mentioned.

HollowPoint