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Beeman qb chief leaks when fired

Hi, I have a beeman QB chief 1 (.22) and it blows most of the air out of the side right under the breech when fired the pellet still has around 600 fps with the leak (used to be 800-900fps) the tank and everything holds pressure it’s only when I fire. If anyone knows how to fix this I’d greatly appreciate it.
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Hello everyone. I just purchased my first PCP which is the QB Chief 177. Can anyone post how they have their gun adjusted and what pellet they use? I have watch tons of videos' on PCP's but not a whole lot about the QB Chief 177, just mostly unboxing an some features not much else.... Thanks!
You really need a chronograph. The only things to adjust are your hammer spring tension and fill pressure. Fill to max psi (2000psi) then shoot and record velocities down to 1000psi or so. Not a bad idea to record estimated pressures along side of velocity every 250psi or so. I know the gauge isn't great, but get it in the ballpark.

If velocities start low then climb much higher and drop suddenly, you could add striker/hammer tension to help flatten velocities up. Being non regulated, they'll never be flat, but you can get good enough for out to 50 yard target if that's what you're after.

If velocities start high and drop each shot, back off striker tension, until you get a decent velocity curve (low, slightly high, low again).

To adjust striker/hammer tension you'll need an allen wrench, 4mm or so (I've forgotten exactly). In the rear of receiver there's a hole to adjust. If you don't have access to a chrony, set up a target to the furthest distance you plan to shoot regularly (recommend 40 to 60 yards max). If shots land low, then raise beyond expectations as pressure drops then drop again add some striker tension. Post fresh target and repeat until they're grouping good. If you get pellet spiraling (usually 45+ yards), go to a heavier pellet or back off striker tension until it stops.

Also, I don't know if they have changed the valve stem material (poppets) on newer models or not, but probably a good idea to store these guns at low pressure, probably 300psi to 500psi. Otherwise you risk running into valve stem seal issues...

Oh, and keep an eye on your bolt o-rings! If they get chewed up, you'll have to smooth out the lead.
 
If you don't have a chronograph you can still get some idea of your shot curve by shooting paper at a distance of 50 yards or so. Take a sheet of cardboard or several sheets of paper and mark a long series of dots on them then give the gun a full charge. What you're going to do is shoot from a fully supported position and shoot one shot at each dot keeping track of each one and record your pressure every five shots or so.. As the velocity increases your shots will start to rise, then as the velocity levels off you might get 15 or so shots at the same height, then the point of impact will start to lower.

This won't tell you your actual velocity, but it will tell you the pressure that you should charge to to get your peak velocity, how many shots you can expect at that velocity and at what pressure you should recharge.