Hatsan BullBoss .25 Modifications and Slug Testing

[VaporTrail]

just FWIW, when I stretched my hammer debounce spring a little too much, it went too low and actually prevented the hammer from sliding back to the cocking position. You may experience something similar.

As for the shims, I've never tried using them, but when I put in a fresh AT44 HS in the Boss, it caused a failure to cock. After the spring got squeezed and settled, it was able to cock again. Seems like the auto-indexing doesn't work as good as it used to as well; the cover can't be too tight otherwise the mag can only be advanced manually.

60FPE should be doable.

[Rallyshark]

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.

You flat out don't have the spring to get to that speed you want.  You aren't gonna gain a whole lot with the 5mm shim I don't think.  I still think you need to figure out why that heavier spring won't work right, and I think it has something to do with the how the spring is sitting over the trigger.  The gun should be able to make more power than it is for sure.  I don't know if 18 shots at 62 fpe is going to be achievable.  That will be pushing it in the efficiency department, but it may be possible.  It is hard to say, given that you can hardly even get to that power for one shot. 

[Jzizzle]

I switched back to the Nova Spring and used shims so it would not come out of the rear seat.  Peak was 834 fps with NSA 36.2gr.  Although I didn't gain any fps, the trigger wasn't very stiff/heavy as it was before so the previous test definitely had some interference with the trigger/sear. 

Still have to do some more tweaking or may just get a different spring.  I know there is more power there...

Next I decided to use .22 peek seat.  I also switched back to oem hammer spring with no shims.  Using the valve spring retainer with enlarged holes.  At max preload ( I think it was 10 turns) I have a high of 898fps.   The bigger valve seat gave me about 60fps gain over previous tests.  While testing with different preloads each turn gave an increase in fps until the sear would no longer catch.

A string at max  NSA 36.2gr
1 879
2 884
3 898
4 887
5 885
6 878
7 882
8 874
9 871

I only have 1 mag with decent es at these speeds.

Next I will switch back to a heavier hammer spring and continue the testing.

[Rallyshark]

Now it is starting to look better!

[VaporTrail]

agreed. If you can get into the quarter 9s with 36gr slugs, that's going to be quite the thumper.

[Jzizzle]

What I can't seem to figure out is why each different configuration has a certain point of preload where the velocity begins to drop. 

Now with the most recent test it continues to gain fps all the way to the point where the spring is fully compressed.  If I can get a heavier spring to act in this manner I don't see why I couldn't  get ~950fps max and tuned down to ~900fps for strings.

[Rallyshark]

What I can't seem to figure out is why each different configuration has a certain point of preload where the velocity begins to drop. 

Now with the most recent test it continues to gain fps all the way to the point where the spring is fully compressed.  If I can get a heavier spring to act in this manner I don't see why I couldn't  get ~950fps max and tuned down to ~900fps for strings.

Hopefully, you can get the stiffer spring to work, because it may not have to lean on the valve as much.  That would increase your shot count most likely.

[Jzizzle]

I went to 4 hardware stores and left empty handed at each one.  I will have to source the spring online.

[Rallyshark]

That's a bummer   The only one I've found the spring that works at is Ace.  I've found it at a few different Ace stores fwiw.  You could probably find one online at McMaster Carr or some other spring store.  Just measure the OD/length of the factory spring and start looking.  I still think that Nova spring should work, and don't understand why it won't.  I've used springs that where a 1/2" shorter, some that were longer with no ill effects.  There be some weirdness going on there 

[Jzizzle]

I have a spring on order to test out.

Also, will run all the different types of ammo again at some point once I settle on final tune.

Have some grizzlys on order too.

[Jzizzle]

I was thinking about opening my ports further...from .187 to .203.  what's the thoughts on this.  I don't want to loose too much efficiency as I want 18 shots per fill within 3%. 

[Rallyshark]

I was thinking about opening my ports further...from .187 to .203.  what's the thoughts on this.  I don't want to loose too much efficiency as I want 18 shots per fill within 3%.

Correct me if I'm wrong, but I don't think there is enough material in the transfer to handle opening it up that much.  That is, if Hatsan hasn't changed the design, and they haven't on any I've seen at least.  If you can't open the transfer any more than it is, then opening the other stuff is a waste of time and can actually cause a loss of efficiency and power.  I pretty sure 3/16" is gonna be the limit on that transfer, unless you want to try and make one that will handle it. 

I know I keep beating a dead horse, but any mods you make at this point to increase power is a dead end, UNTIL you figure out why the gun won't make more power than it is already.  I feel like the numbers are low, and something just isn't right with the gun.  I don't know what it is, or what is causing it, but something is just a little bit off somewhere.  It seems like it is 5-10 fpe below where it should be able to be on the top end.  It could be transfer port leak, or hammer sticking/binding, or even spring catching, but I don't know which it is.  You're going to be hard pressed to get the string you're looking for with the gun working perfectly, especially on a 200 bar gun that isn't quite happy.  I wish I could think of what is going on with it, but I'm at a loss myself 

[Jzizzle]

I hear ya buddy, and I welcome all ideas and recommendarions.
 When I swap the spring I will inspect the orings #2402 at transfer port.

[tejon]

Subscribing.... fellow bb owner here.. got to ask.. have you checked valve lift?

[VaporTrail]

Hmm...tejon might be on to something. I've gone through 6 Boss cylinders and 4 have given me different readings. The other two were modded and were fairly close to each other in terms of performance.

I tried replacing a valve spring in one of the cylinders, and it was fart city.  I thought I'd compress it a little, so I put the degas tool on and cranked it all the way down. Left it for several days.

Now the spring is pretty darn loose. There's no pressure in the cylinder, but I can compress the valve pin with my thumb. I think I left it compressed for a little too long.

Anyways, I found out that different cylinders will yield different FPS numbers. Perhaps that is what's going on here?

Just something to further obfuscate an already obfuscated situation.   

[Jzizzle]

Not so much the cylinder that makes the difference but yes the valve assembly does.  I have 2 valve assemblys and they both acted very differently over the chrony before I modded the current one.  The valve stem was the only difference I could find between them.

How do I check the valve lift?

I think Donny is on to something though...will disassemble tomorrow.

[tejon]

How do I check the valve lift?

[/quote]

look at the hammer, from the right side.... unscrew the cylinder almost all the way, then slowly screw it in watching the hammer, when the hammer start to move stop. then back off slightly and try again, when the hammer starts to move stop. then look at the gap between the valve assembly and the hammer tube... should give you an idea... .

I suspect there is a bump stop inside the hammer tube, to adjust lift, I think on mine it moved, and I have a 5mminch of available lift (my rifle is bottoming out on the valve body, so about 2.5mm actual lift) .,, suffice to say, loud as c//p and only a few innacurate shots,, 

[KnifeMaker]

Tow other areas to look at that HobbyMan2007 and I tried.


First He, and I shortened a very stiff spring, and added a smaller dia spring in side of it. the shorter length prevents hammer bounce, and the small dia spring give it an even higher rate.


My self, on several guns, I added a  piece of brass rod turned down to fit  inside the hammer where the spring sits to increase the weight of the hammer. This helps greatly to open the valve fully at higher pressurizers. the short dual springs will increase shot count and give higher fps at the same time.


Knife

[Rallyshark]

Tow other areas to look at that HobbyMan2007 and I tried.


First He, and I shortened a very stiff spring, and added a smaller dia spring in side of it. the shorter length prevents hammer bounce, and the small dia spring give it an even higher rate.


My self, on several guns, I added a  piece of brass rod turned down to fit  inside the hammer where the spring sits to increase the weight of the hammer. This helps greatly to open the valve fully at higher pressurizers. the short dual springs will increase shot count and give higher fps at the same time.


Knife

That does work, and I've done that on a couple of guns.  Unfortunately, the HS adjustment on this gun requires using a 4mm allen that goes through the spring.  The spring OD on the BB is so small, that adding a smaller spring inside it would make it so you couldn't adjust the tension   There's no easy way to pull the spring, adjust, re-install it either.  They don't leave a lot of wiggle room inside the Bullboss for changing the way it works.  To make it worse, the spring runs right over the top of the trigger assembly, so a bow in the spring will cause all kinds of crazy stuff to happen too.   This is a lot of the reason I modified the Bullboss I had so I could adjust it without the 4mm allen   I used dual springs on that one.  Not everyone is willing to go quite that for down the rabbit hole though,lol. 

[Jzizzle]

I have been having an issue with a slight air leak at the transfer port.  Trying various size o-rings with no success.  It would seal for a few shots before it would give.  I used gasket maker along with o-rings and this is holding up so far.

I was also having an issue with my valve seat. I damaged my peek seat on removal. (should have just left it alone in there)  I then was using an oem delrin seat drilled out to .210 and this failed on me and began to leak after a few hundred shots.  I then used an oem delrin drilled out to .203 for a few hundred and no issues......that is until my valve stem broke right at the o-ring groove.  Luckily I have an extra valve stem.

I have no clue when these stiffer hammer springs are getting here from china, so that is on hold.

Now with all the issues addressed above..
Here is a 18 shot tune with NSA 36.2gr

OEM Valve Seat .203
All ports .1875
Enlarged Valve Spring Retainer Holes
Stock Hammer Spring

 1.  832
 2.  841
 3.  838
 4.  842
 5.  842
 6.  846
 7.  849
 8.  848
 9.  848
10. 854
11. 848
12. 847
13. 847
14. 846
15. 843
16. 839
17. 828
18. 827

HI-     854
LO-    827
AVG-  842
ES-    27
SD-    7

Efficiency- 1.32
3000psi-2200psi

From previous testing with a peek seat vs delrin, I know speeds would be increased from current to anywhere from 30-60 fps.