Hatsan BullBoss .25 Modifications and Slug Testing

these are the springs I have on order, blue and red with 55mm length.  I got the green ones already but they are way too stiff.

thanks

The Yellow springs linked above allow a 4mm hex to pass the ID. The blue, red and green 8MM die springs had a smaller ID just enough to block the 4mm hex.

Chucked up the blue spring in the lath and used a cobalt drill bit to open the inside a bit, very fine cut. Surprisingly the spring held up well in the 3 jaw chuck.

Another way to fine tune a die spring, length and section.

A bit of an update here with 36.2 NSA slugs.  These slugs stack at 70 yards!


Testing with yellow die spring didn't net me any positive gain.

I went back to the Nova spring with the oem spacer removed.  This gave me 9 shots 900-930 fps.  Seems like the spacer was the culprit from previous tests.  Only downside here is I cant get 2 mags consistently at these speeds, cocking is much stiffer and noise has increased.

I am satisfied here.  I feel I have reached the upper limits here.  There is more power to be had if shot count wasn't to be considered. I need to reduce speeds to mid 850s for 2 consistent mags.  If a bigger reservoir or higher fill was available that would be a different story.


I appreciate everyones input and help through out this build.

Thanks!

Awesome... congrats on finishing your project.

And thank you for the tip on the 36.2 nsa... will try them in the future...

Yes, NSA 36.2 did the best for me.  NSA 29 were also accurate but I prefer the heavier slug.  The Varmint knocker 32.8 were also accurate but a much higher cost then NSA.    You can look back at all the slugs and weights I tested.  These 3 slugs performed the best for me with NSA 36.2 being #1.

Hi guys, wonderful post full of experienced gurus suggestions (in fact one of the best I got chance to read) for any Bullboss owner.
As a matter to be fair and give you a brief intro about me, the fact is that my background is about centerfire and reloading, I have several airguns also (Gamo) but never awake too much my interest. Some weeks ago, due the COVID mess I tried with my first PCP, a Hatsan Bullboss .22... well, I just got so impressed that I fully reconsidered my wrong opinion about the airguns.
I like to tweak my practical guns to improve it and get the maximum in any sense (any gun with a fair engineering might be improved).
There comes this thread and enlighten me about the key points to tune up this little marvel.
Although everything seems quite clear, I have a doubt about the so called PEEK seat, I do not know if there is any schematics where explained.
I have a question that you might know. Living in Barcelona (Europe) I'm getting disappointed about the spare parts for the Hatsan line, in the European stores do not seem to be a single one with the whole line of spares, so even is difficult to id the parts, my specific questions are:
Is if the AT or BT line compatible parts with the bullboss or what models share parts.
Is feasible to swap the caliber from .22 to .25, the changes involved (apart of barrel and magazine) if any and if worth it in the output sense (discarded to sell this and get a 6,35 as here the prices are around 600USD for any bullboss and is not easy to sell used ones even with only few shots), despite that, I'm so hooked that I'm wondering already to some other models when this one is set with a satisfactory results.
Are the mods exposed here the best options to get the most long range shots?
Sorry for so long thread but I think this one is too useful to let it down without complete some other details.

Artur

Artur...

For your modifications, be sure to take a look at RallyShark's modification thread. There is a link in the beginning of this thread. Jzizzle very closely followed what was done in that thread. As for your questions on the PEEK valve seat, RallyShark's thread has measurements that he used to fabricate the valve seat.

As for your spare parts, you should be able to order from Hatsan's site. Another option is the Chambers website...they have parts there as well. Speaking of parts, the Bullboss is the bullpup version of the AT44, so most the parts are interchangeable. Don't order BT parts...that's a different platform.

As for changing calibers, it's a fairly straightforward procedure. You'd need a barrel, probe, magazine and if I remember correctly an upper block. Your best option would probably be to find a .25 Bullboss that is in need of repair; it'll be much cheaper that way.

I'm a huge fan of the Bullboss, despite some of its quirks. It was my first and second PCP. Then I sold the .25 version and later on picked up RallyShark's .22 Bullboss.

Sometimes they might need a little extra attention to perform properly, but when the problems are addressed, they are an absolutely wonderful rifle.

Good luck and may she bring you much joy!

You just need some 3/8" PEEK rod to make the valve seat, and it isn't that expensive.  It goes for about $12-15 here from Amazon.  Just measure the factory one, and match it for the most part.  The biggest difference will be the size of the hole in the seat(.210" max).  I think you're going to have a lot of fun, especially since you have all the tools to do it with

The extra length of the hammer should reduce your lock time too, since the distance the hammer has to travel to the valve pin is reduced.  That could help the accuracy as well.  Nice work!

Shots in the dark here, I cant find any info on the air cylinder O-rings needed to reseal. I have a leak and want to reseal the entire cylinder. Hatsan is perennially out of stock.