Hatsan BullBoss .25 Modifications and Slug Testing

[Jzizzle]

Yes, hole in breech above the transfer also opened up.  I pretty much drilled thru the breech into the cylinder carrier port.  Then obviously drilled transfer port, barrel port and valve port separately.  Every thing is .1875"

Prior to reassembly, I lined ports up perfectly and then used a small blade to mark it on the outside so when I remove the cylinder I know exactly where it needs to be. 

[Jzizzle]

Hades pellets arrived today.
NSA, AVS, and Griffin slugs coming next week.

Hopefully I hear back from Hatsan by Monday to order the Nova Star hammer spring.

In the meantime I'll work on the valve seat and valve spring retainer.

[Jzizzle]

Using Griffin 28gr deep hollow base as the test slug here are comparisons for hammer preload and listed additional  changes.  All 2900psi fill pressures.

TEST 1
Ports .1875
oem valve seat .1875
OEM Valve Spring Retainer

  0 - 619 fps
-1 - 714 fps
-2 - 764 fps
-3 - 816 fps
-4 - 850 fps
-5 - 887 fps
-6 - 890 fps
-7 - 905 fps

TEST 2
Ports .1875
Enlarged Valve Spring Retainer holes
PEEK valve seat .212

  0 - 759 fps
-1 - 800 fps
-2 - 850 fps
-3 - 895 fps
-4 - 922 fps
-5 - 894 fps
-6 - 838 fps


TEST 3
Ports .1875
OEM Valve Spring Retainer
PEEK valve seat .212

  0 - 736 fps
-1 - 787 fps
-2 - 844 fps
-3 - 877 fps
-4 - 914 fps
-5 - 935 fps
-6 - 878 fps

TEST 4
Ports .1875
OEM Valve Spring Retainer
PEEK valve seat .212
Stiffer Hammer Spring from NovaStar

  0 - 897 fps
-1 - 953 fps
-2 - 868 fps
-3 - 801 fps


Any idea as to why Test 4 hammer adjustments reduce fps after 1 turn preload?  The spring is same length, only stiffer.

Only combo I didn't try was the enlarged valve spring retainer holes with the stiffer hammer spring.

[Jzizzle]

Did more accuracy testing with various weights with Griffin, NSA, AVS  and Varmint knockers.

Only ones that work well in this bullboss are NSA 29gr and 36.2gr.  AVS 28gr. Varmint Knockers 32.8gr. 
Everything else is poor at 22 yards.

[Jzizzle]

Accuracy results at 22 yards continued.

AVS 28 gr - .338"
AVS 30 gr - .814"
AVS 32 gr - .480"

Griffin Deep Hollow Base 24 gr - .811"
Griffin Deep Hollow Base 25 gr - .753"
Griffin Deep Hollow Base 26 gr - .643"

Varmint Knockers 32.8 gr - .379"

NSA 38 gr -     .903"
NSA 36.2 gr -  .459"
NSA 33.5 gr -  .743"
NSA 29.5 gr - 2.051"
NSA 29 gr -     .660"
NSA 26.8 gr -  Off paper >1.5"

[Rallyshark]

Using Griffin 28gr deep hollow base as the test slug here are comparisons for hammer preload and listed additional  changes.  All 2900psi fill pressures.

TEST 1
Ports .1875
oem valve seat .1875
OEM Valve Spring Retainer

  0 - 619 fps
-1 - 714 fps
-2 - 764 fps
-3 - 816 fps
-4 - 850 fps
-5 - 887 fps
-6 - 890 fps
-7 - 905 fps

TEST 2
Ports .1875
Enlarged Valve Spring Retainer holes
PEEK valve seat .212

  0 - 759 fps
-1 - 800 fps
-2 - 850 fps
-3 - 895 fps
-4 - 922 fps
-5 - 894 fps
-6 - 838 fps


TEST 3
Ports .1875
OEM Valve Spring Retainer
PEEK valve seat .212

  0 - 736 fps
-1 - 787 fps
-2 - 844 fps
-3 - 877 fps
-4 - 914 fps
-5 - 935 fps
-6 - 878 fps

TEST 4
Ports .1875
OEM Valve Spring Retainer
PEEK valve seat .212
Stiffer Hammer Spring from NovaStar

  0 - 897 fps
-1 - 953 fps
-2 - 868 fps
-3 - 801 fps


Any idea as to why Test 4 hammer adjustments reduce fps after 1 turn preload?  The spring is same length, only stiffer.

Only combo I didn't try was the enlarged valve spring retainer holes with the stiffer hammer spring.

On the plus side, it looks like that PEEK seat gave it a bit more oomph!  I would go with the opened up valve spring retainer and the stiffer spring for sure. 

Now, the odd part is the speed decreasing after adding more preload?  My theory is that the de-bounce is sticking and causing excessive hammer bounce, and that the hammer is coming back and hitting the valve.  Did you notice the gun sounding "funny" when you added more preload and the fps decreased?  It could also be the de-bounce(wishbone) is sticking worse when there is more hammer force causing excessive drag on the hammer...  Basically, all my theories are centered around the de-bounce malfunctioning at this point...  The only other theory I have right now is there could be a cut o-ring somewhere that only leaks when the pressure during the shot cycle is high enough.  All guesses right now though?

[Jzizzle]

Yes next I will swap the valve retainer for the one with bigger holes to see what effects it has with the heavier hammer spring.

When I swapped the springs I also replaced the 3 barrel orings.  Inspected the transfer port orings and valve orings.... everything looks good. 

My debouncer is not riveted, the arms are 2 separate pieces.  If I order this part from Hatsan, is it the newer 1 price design?


As to the slugs.
AVS 28gr did really well but they fit loose in magazine and tend to fall backwards and jam the magazine.  So because of this I won't run them.

Varmint Knockers 32.8gr are awesome out of the bullboss.

NSA 36.2gr did great too.  These are also half the price at the Varmints so I will tune BB and dial.in the scope for these.  I have these on order.  I'd like to sling these around 950fps.

We'll see what we can make happen.

[Rallyshark]

That de-bounce in there now is definitely not going to help.  I shot you a PM, but it you may or may not get the good design from Hatsan if you order one.  Order the one for an AT44, that is the only chance you'll get the good one.  Don't bother mentioning why to Hatsan, they will argue that the two piece is better and they will be wrong.  I've fixed 3 separate guns with that two piece design, and there have been many others on here that it caused problems for.  I would LOVE to talk to who or whom at Hatsan that decided to make that change 

36.2 grain at 950 may be a tall ask out of a Bullboss.  I'm not saying it can't do it, but I don't think it can with any usable shot string.  If it was a 250 bar gun, it would be no problem.  Unfortunately you only have 200 bar to work with.  You could probably go to a 3100 psi fill safely, but I wouldn't recommend any higher than that.  I know people that have, but that's up to them if they want to play with fire.  Besides, you could find they aren't as accurate at 950 fps anyway.  Slugs tend to be kind of picky about the speeds they work well at in many guns.  I think 900 fps would be closer to realistic, and still very devastating! 

I'm hoping some of the other folks on here will chime in on your odd decreasing fps when you add more that one turn preload with that HS.  That is rather weird.  I have theories, but without the gun in my hands I'm just guessing   Let us know what you find out after you get to do some more testing!  You've already made good progress!  Also, go ahead and shoot a string with it at the higher fps setting.  The speed should increase down the string a bit I think.  If you get a steady declining string, you're likely at the highest setting that will work(prior to decreasing with more turns).  I doubt that's the case given the numbers you posted.

[Hobbyman2007]

It looks like you found the “magic” bullet for that gun. Concentrate on playing with that one at different speeds and surely the groups will shrink. Once that’s all figured out and you have the speed and bullet it prefers. Order a but load of them. Good job on the tuning.

[VaporTrail]

I can't recall if I saw mention of the valve spring being replaced. Have you checked your valve pin for any deformity?

I still think you should be slinging lead much harder than that. Those 900ish spikes and then massive drops may be the start of a breadcrumb trail that might lead to more power.

Just an observation, but a stock .25 Boss slinging 28.5gr Benjis at 925 vs. an almost modded-to-the-hilt Boss slinging the same weight slugs at 953 peak doesn't add up.

My two .22 Bosses have a major difference with the same scenario. My stocker will sling 28gr EJs at 840. The RallyBoss will absolutely launch 28gr slugs at 974, and that's not even max HS adjustment; at full tilt she'll send the 28s at over 1000FPS.

There's a monster lurking in your Boss...we just have to try and figure out how to release it.

[Rallyshark]

It looks like you found the “magic” bullet for that gun. Concentrate on playing with that one at different speeds and surely the groups will shrink. Once that’s all figured out and you have the speed and bullet it prefers. Order a but load of them. Good job on the tuning.

Denis, do you have any ideas on the fps decreasing after more than one turn using the heavier spring??  It is a Nova spring, and the exact same diameter of the stock spring.  It is slightly shorter, but that decreasing fps has me a bit stumped...

[Jzizzle]

I can't recall if I saw mention of the valve spring being replaced. Have you checked your valve pin for any deformity?

I still think you should be slinging lead much harder than that. Those 900ish spikes and then massive drops may be the start of a breadcrumb trail that might lead to more power.

Just an observation, but a stock .25 Boss slinging 28.5gr Benjis at 925 vs. an almost modded-to-the-hilt Boss slinging the same weight slugs at 953 peak doesn't add up.

My two .22 Bosses have a major difference with the same scenario. My stocker will sling 28gr EJs at 840. The RallyBoss will absolutely launch 28gr slugs at 974, and that's not even max HS adjustment; at full tilt she'll send the 28s at over 1000FPS.

There's a monster lurking in your Boss...we just have to try and figure out how to release it.

Valve spring is original, only with the spring retainer holes slightly enlarged.

The valve pin is in good shape.

I don't think we can compare fps of equal weight pellets to slugs.  Lots of variables that will effect that.  For instance at same preload 25gr Jsb is 990fps vs 25gr slug at 940fps. 

[Jzizzle]

I've swapped back to OEM spring and the declining power at more preload has been remedied. The debouncer was not the issue. Spring may be kinking, who knows.  Just ain't working right.  As a side note with the heavy hammer spring, the trigger weight has also increased and if I try to lighten it up the sear won't catch.

I will see if I can find some shims to use with the OEM spring to increase the tension a bit.

Current power is 60fpe with 36.2gr NSA slugs.

[VaporTrail]

I can't recall if I saw mention of the valve spring being replaced. Have you checked your valve pin for any deformity?

I still think you should be slinging lead much harder than that. Those 900ish spikes and then massive drops may be the start of a breadcrumb trail that might lead to more power.

Just an observation, but a stock .25 Boss slinging 28.5gr Benjis at 925 vs. an almost modded-to-the-hilt Boss slinging the same weight slugs at 953 peak doesn't add up.

My two .22 Bosses have a major difference with the same scenario. My stocker will sling 28gr EJs at 840. The RallyBoss will absolutely launch 28gr slugs at 974, and that's not even max HS adjustment; at full tilt she'll send the 28s at over 1000FPS.

There's a monster lurking in your Boss...we just have to try and figure out how to release it.

Valve spring is original, only with the spring retainer holes slightly enlarged.

The valve pin is in good shape.

I don't think we can compare fps of equal weight pellets to slugs.  Lots of variables that will effect that.  For instance at same preload 25gr Jsb is 990fps vs 25gr slug at 940fps.

possibly, yes. But that lower FPS with the slugs could be an indicator that the slugs are either too large and suffering friction in the barrel, or they are too small and air is being wasted. Is that the stock barrel? Are there perhaps tight spots or a shoddy choke that's robbing you of precious FPE?

[Rallyshark]

I can't recall if I saw mention of the valve spring being replaced. Have you checked your valve pin for any deformity?

I still think you should be slinging lead much harder than that. Those 900ish spikes and then massive drops may be the start of a breadcrumb trail that might lead to more power.

Just an observation, but a stock .25 Boss slinging 28.5gr Benjis at 925 vs. an almost modded-to-the-hilt Boss slinging the same weight slugs at 953 peak doesn't add up.

My two .22 Bosses have a major difference with the same scenario. My stocker will sling 28gr EJs at 840. The RallyBoss will absolutely launch 28gr slugs at 974, and that's not even max HS adjustment; at full tilt she'll send the 28s at over 1000FPS.

There's a monster lurking in your Boss...we just have to try and figure out how to release it.

Valve spring is original, only with the spring retainer holes slightly enlarged.

The valve pin is in good shape.

I don't think we can compare fps of equal weight pellets to slugs.  Lots of variables that will effect that.  For instance at same preload 25gr Jsb is 990fps vs 25gr slug at 940fps.

possibly, yes. But that lower FPS with the slugs could be an indicator that the slugs are either too large and suffering friction in the barrel, or they are too small and air is being wasted. Is that the stock barrel? Are there perhaps tight spots or a shoddy choke that's robbing you of precious FPE?

Paul, his numbers are far enough off that I doubt it comes down to the barrel or ammo.  Pellets of the same weight pretty much always make more fps than slugs.  I do would recommend a good barrel cleaning at this point though   I PM'd him a couple of other stuff to check out too.  Hopefully, he'll get this BB singing soon!  By the mods, it should be a beast.

[VaporTrail]

hopefully he gets his beast unleashed. I'm excited for him! Almost makes me want to buy a .25 Boss again. 

Lol...my wife is gonna clobber me pretty soon. 

[Jzizzle]

Thanks everyone for your help and input.  I do greatly appreciate it.

I will be sure to update everyone on the continued path on my bullboss.

[Jzizzle]

I took apart the bullboss once again and added shims for a total of 3mm to be used with OEM spring. 

Unfortunately it's too late in the day and the chrony doesn't have enough daylight to register the shots.

More to follow.  Eagerly awaiting results!

[Rallyshark]

I took apart the bullboss once again and added shims for a total of 3mm to be used with OEM spring. 

Unfortunately it's too late in the day and the chrony doesn't have enough daylight to register the shots.

More to follow.  Eagerly awaiting results!

We look forward to seeing the results as well

[Jzizzle]

I'm all out of the 28gr slugs I was using previously so from here on out tests are with the ammo I plan to run.. NSA 36.2gr.
 I ran two tests using stock hammer spring.

1mm shim
Preloads
 0. 410
-1. 490
-2. 575
-3. 641
-4. 696
-5. 733
-6. 777
-7. 811
-8. 846
-9. 771

3mm shim
Preloads
 0. 595
-1  664
-2. 716
-3. 763
-4. 796
-5. 828
-6. 846
-7. 756

Strings with 3mm shims at pretty much max of 840fps avg yields only 6 consistent shots before rapid drop.

In order to get 18 shots within 2% I have to drop to an avg of 790fps.

One thing to note when I swapped from 3mm shim to 1mm shim, I broke my debouncer spring upon reinstall, got kinked and is no longer usable.  I replaced with a firmer spring that I cut down.  Not sure what impact that has though. 

Do you guys think it's worth it to try with maybe 5mm shim?  It appears that the shims change power at different preloads but thus far has no impact on max fps.

Trying to achieve 880fps avg with NSA 36.2gr for 18 shots.