Pneuma/ can't adjust the hammer spring/help me understand something

[darryl]

OK, I put a small hex wrench in the hole in the hammer. Then I inserted the 4mm hex into the adjustment hole and felt it seat. I can't turn it without fearing to damage something. It's that hard to turn in either direction, CW or CCW. It's like it's frozen or maybe corroded together in there. What to do? Better yet, how to take this down to get this problem corrected so I can adjust the hammer spring tension ?
thank you,
Darryl

[Rescue912]

Put a few drops of PB Blaster (or some other break-free type oil) in there and let it sit barrel down overnight then try again. Mine was stiff, but not that stiff.

[rsterne]

I figured the one I worked on was loctited, I was afraid I was going to break the allen key.... They are fully clockwise from the factory, and you have to turn them CCW to increase the preload.... I have been told by a very skilled airgunner who took his apart that they are NOT loctited but that the screw has been "squared" off on the thread portion to jam tight.... I never took the one I worked on apart, but once I got it to move once, it adjusted easily after that.... in fact too easily, it kept screwing in to reduce the preload back to stock.... Others I have talked to said theirs were loctited....

Bob

[darryl]

So I won't know what I have until I take it apart. Maybe it's been squared off. Maybe it's been set in Loctite. Well, in for a penny. In for a pound. This particular Pneuma is not a very friendly PCP.
Thanks for the input guys,
Darryl

[rsterne]

One way or the other, adjusting the hammer spring is NOT something Hatsan want you to do, obviously.... I don't think you can fault the gun if you're having a problem with that.... whether it's loctited, squared off, or staked over with a big hammer and punch.... When you start modifying a gun, it's not really fair to criticize the manufacturer because they made your job difficult, IMO....

Bob

[darryl]

I din't want to seem to sound critical.

[darryl]

I've amended the title of this thread because I need some help in understanding what's going on. Here's what I mean: from a starting fill pressure of only 140 bar/2000 psi I see a satisfying increase in accuracy, from the first shot through the 24th shot. If I fill higher than 140 bar, (to 180 bar) the rifle's accuracy starts off all over the place, slowly getting tighter as the pressure drops off. I just don't get it AT ALL. Need a little help.
darryl   

[rsterne]

It could be that the velocity is different at 180-200 bar than it is at 140 bar and below.... Even a slight difference in velocity can cause the pellet to exit during a different part of the barrels travel as it vibrates from the shot.... Barrel harmonics are strange things.... The other possibility is that at pressures over 140 bar the tank is tilting up or down slightly against the barrel bands and pushing or tugging on the barrel bands.... either causing errant shots directly.... or once again, affecting the barrel harmonics....

It could also be that the pellet simply doesn't like the higher pressure pulse.... Even though the velocity in a PCP might be exactly the same at 190 bar and 120 bar.... the way the pellet gets to that velocity is COMPLETEY different.... In the first case, it receives a short, powerful pulse, causing almost all of the acceleration in the first few inches of travel.... In the second case, the valve is open much longer and the pellet sees more of a leisurely "shove" accelerating in a more gradual fashion.... If the pellet is pure lead (ie soft) then it could easily be a significantly different shape when it leaves th muzzle.... If you could capture the pellets without damage and examine them, you may find that the ones fired with the higher pressure pulse have a more cylindrical skirt, flared out by the higher initial pressure....

Just some random thoughts, any or all of which could be causing the change in accuracy....

Bob

[darryl]

Thanks for the perspective, Bob. Maybe of interest, is that I am now down to one barrel band in use. I had modified one band to only support the air tube. Then I found out that the weight of the LDC pulled the barrel down until it touched and kept contact with the cut-down barrel band. Accuracy was not consistent at all. So now with the one whole barrel band in place and the lower fill pressure, accuracy is looking good.
I'll keep in mind what you  say here, and try to figure out if I need to leave well enough alone now.  But, a quick question with regard to free-floating the barrel: would a full shroud help the cause? I guess there's only one way to find out.
thanks,
Darryl

[rsterne]

I've never had a shrouded gun.... so can't comment....

Bob

[darryl]

OK, I've gotten into it, and removed the trigger group, and the air tank. I could not get the hammer adjustment group to come out, though I've seen a video on thhe repeater, and it shows this group just being pulled out. I could not even tap mine out. But I did break it loose. Perhaps it was over-tightened at the factory? Anyway it was turned all the way in clockwise, and I had to turn it counterclockwise to get it to move. I guess it was on full power from the factory.

Well, as luck would have it (my luck) the plastic ball and it's spring fell out. How do I get these two back in place? Without them I was able to cock the mechanism, then push the safety in to fire it. I'm reminded of a mod to make the safety a manual operation. Anyway what's the procedure to put that plastic ball back in place? anyone?
thank you,
darryl

[rsterne]

CW = MINIMUM
CCW = INCREASES PRELOAD

Bob

[darryl]

thanks Bob; twice. Now I'm really curious. The one time I had use of a chronograph with this rifle it was pushing H&N FTTs (14.66 grains) at 937FPS /28.6 FPE. That was with the tension adjustment turned fully in. Maybe that's why the accuracy was so erratic at full fill (200 bar). I'm not suggesting that I go back to 200 bar. But I think I need to try to find a new balance. A little bit more pressure, maybe to 170 bar, and a bit more pre-tension on the spring, perhaps. One way to find out (once I get that little plastic ball back in place).
darryl

[rsterne]

On the gun I played with.... the peak velocity occurred at ~160 bar (950 fps - 28.6 FPE) with the 4% range from 185 bar down to 125 bar with 14.3 gr. pellets.... Moving up to 18.1 gr. pellets, the peak velocity occurred at ~150 bar (900 fps - 32.6 FPE), same usuable pressure range....

With the hammer preload screwed out 2 turns.... and using 18.1 gr. pellets.... the peak velocity occurred at ~160 bar (~920 fps - 34.0 FPE).... the 4% range was from 200 bar down to 130 bar.... You might try heavier pellets, especially if you increase the hammer spring preload....

Bob

[darryl]

Hi Bob,
I decided to add two turns out earlier. looks like I'm following you around, eh? I've got a new tin of 18.1 Jumbo Heavies. Can't wait to give them a spin. Gave the crown a bit of a polish as well. Looked a bit rough under an eye loupe.

But how to get that plastic ball back in there for the safety button? Any ideas?

[darryl]

Of course I got the little plastic ball back in. Had some problems with reassembly, but it was a good way to learn the rifle. It seems if I want a better shot count I'll have to plug some holes to restrict some air. Can you PM me on the process, and what is required? I may or may not be able to take that project on. I've found that as it is, the rifle shoot very accurate if  start at 145 bar. But with so little air supply I only get 20 good shots. I'm using the 18.1 Jumbo Heavies. I'm at 2 turns out. I think it's just a waste of air at that setting with no holes plugged, and those two turns.

[rsterne]

Here is a photo of a valve with the bottom 3 holes plugged....



I just drilled and tapped the holes for 6-32 set screws.... not elegant, but it worked.... I've seen the groove filled with JB weld as well.... instead of the screws....

The stems, top to bottom, are <500 fps for Canada (0.150"), one I turned down to 0.120" (about 25 FPE) and a full power 0.100" (~30 FPE)....

Bob

[darryl]

Bob, thank you. I'll see if I can duplicate this. I saved a link to your work over on AirgunHome.com for further review of testing. It's a great piece of work you've done. there.
darryl

[darryl]

you guys see this about regulating the AT44?  http://www.network54.com/Forum/79537/thread/1319493917/Results+of+regged+Hatsan+AT44+in+.22cal+and+.25cal+target+pics+added
darryl

[Stefan]

OK, today i decreased the hammer spring tension fully, and set the regulator to 110 bar. its dark now, and my 4lbs single stage trigger is getting tuned tomorrow, so I ll post shot strings with cpum on Saturday. hopefully I will get more regulated shots than before.