Might be something like a breach oring going bad, or hammer drag, etc, best to dig into it may be simple, may take all of our brains
You may already know this but when adjusting the hammer spring, make sure that the hammer is not rotating by inserting a punch in the hole to keep the hammer from turning. The hammer spring will not adjust if the entire mechanism turns.Here's an explanation by rsterne: http://www.canadianairguns.com/showthread.php?656-Hatsan-25-cal-AT44S-10-Long-Mods
I’m not a Hatsan guy so I don’t know if the At44 came from the factory with a reg. If it didn’t, you have some porting to do.
If you don't see a speed drop even at the minimum hammer spring preload, maybe is time to switch to a softer hammer spring or cut some coil from the spring. Can happen if the regulated pressure is considerably lower respect to the original fill pressure.
Just a couple of questions….not having used that regulator...and stuff you already know.But sometimes we get kind of narrow focused.Assuming there is no mechanical problem and everything is working normally.1. Does it reduce velocity if you back the spring tension way off. Would not make for the speed you want, but if it then acts like you’d expect a regulator to act, at least know it works. By testing, could get a ball park idea of what the real world output pressure.2. Plenum size?I expect that at a certain point, more spring tension doesn’t give significant velocity change...basically ran out of pre-regulated air. May not be able to easily change the plenum.
Never cared for the Hatsan .177'sOut of the box they all seemed to shoot hot.Opening ports just compounds that issue.