Hatsan BullBoss .25 Thoughts

WOW. I have entered the black hole of Hatsan tuning. lol. I swapped the outlet valve spring inside the brass cap that one slots a V-groove into when a HUMA is installed...

I left the HUMA set at 130 bar. I did take a few shots that were all over the place. Realllly low speeds, but I had left the hammer spring all the way relaxed. 450fps, then 570 to 670. I did some increased tension hammer turns and some more turns...

Nothing wild but went from 768's with stock spring to 788's with this new spring. I have run out of 25 gr ammo until I relocate where I put my other tin. But my shots that registered over the chrony were no LOWER than 780. And ya know what, this is good data. I will take a photo of the spring I swapped it for but it was a perfect fit, just not as heavy tension.

I read online that in essence the HUMA or any regulator can radically change the factory tune of a non-regulated rifle. We all know this basically...usually the hammer spring needs to be lighter as the air volume is less in the plenum. BUT with this Hatsan's heavy spring it was not letting (I guess) the air escape efficiently...

So by me reducing the resistance of what the hammer face comes against it changed that, clearly. Same rifle, same settings, same ammo, same starting pressure (200 BAR). I hope to mess with it more tomorrow.



This is the factory spring I replaced for this test. Rifle when from being 32/33 ft/lb to mid 34 ft lb...and regulator is still at just 130 BAR. If I go to 150 or max of 170 it then that will be data I'd be happy to see.

Uuugh. lol. I will say I have learned alot, having this hand-me-down rifle scratches and all...I got over my fears of tinkering with HPA. All one can do is make changes in an orderly fashion and go with the flow. Keep what works or revert what got jacked up. 

Reading alot first gave me ideas and a starting point as well as YouTube. I want to come up with something that will help other users. This is same setup as the AT-44 and Gladius rifle. As I mentioned I may get another tube and leave it unregulated. It would be like having 2 different rifles, dunno if anyone has thought of that. I haven't read that it's been approached that way but sure someone has done it?

Adjusted hammer spring two ways, lighter was giving me 746fps with 27gr and this current setting seems to be really jiving at 755 with the 27s. Still at 130 BAR. Not sure of the shot count yet. This is the 27gr Benjamin ammo that I was getting 813avg speeds but extreme spread of 14 SD of 3.7 unregulated. Now it is ES of 7 with SD of 2.