I've an old fas 6004, I put some pellets through the chrono today and fps were ranging from 271 to 243.
It's obviously way too slow and I'll have to try the mods described in the Slofyr's post but my question is... how much a jump of 20/30 fps will affect accuracy? How lower/higher will the pellet hit on the target? (Sorry I'm bad at maths)
I just want to understand if a bad shot is my fault or the gun's... Sometimes I'm sure the the shot was perfect just to find out it went 2cm higher or lower...
My old FAS 6004, many, many years back, had a pellet velocity of about 360 - 380 fps, a tad less than my somewhat similar AP, but even older Walther LP 2.
Your velocity readings are way too low. Something is apparently wrong.
In theory, as long as it's consistent, it should still be fairly accurate. That said, a couple FPS variation out of 250 FPS is a bigger deal than the same variation in a pistol that shoots at 350 FPS.
We have Hammerli AP20's for the new shooters on the team I help coach. The regulator kicks out at about 60 BAR, but the students often don't tend to notice until the pressure is down to around 20 BAR. At that point, the shots are going a couple inches low.
The velocity is that low because something is leaking. The leak is VERY likely to be variable, and if it's after you've cocked it (also likely), the velocity will drop as a function of how long you wait between shots.
SSP’s are intended to be cocked and shot during an interval of 5 minutes max. If your pistol has not been used for a long time, lube the internal seals and pump the piston back and forth a few times without completely cocking (compressing) the pistol. This will help to soften up and expand the internal o-rings, improving air seal and will somewhat increase the velocity.
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