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HW100 .22 FAC shot string is a bit problem. Please help

August 9 2017 at 12:24 AM
umair bhaur  (Login mubhaur)
YF12

Here is the shot string


891
891
888
896
897
895
895
898
896
894
898
892
901
914
897
896
911
912
895
892
897
897
891
890
887
880 Off Reg

Only 3 shots in this string ruin the game. These are 914, 911 and 912.

Pellets used JSB 18 grain. FAC .22 gun 24" barrel. Regulator set at 135 bar as per factory setting.

I serviced the gun and replaced all O rings but 3 shots in a complete string ruin accuracy at 50 50 yards.

Any help please.

 
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AuthorReply
Jason
(Login nervoustrigger)
YF12

Can you adjust the hammer spring tension?

August 9 2017, 1:00 AM 

If so, increase it in a couple of increments (roughly 1mm at a time is good) and take a few shots over the chronograph and report back.

To explain what I'm thinking, almost 2000psi should produce far more than 32fpe with the JSB heavies unless the porting is fairly anemic. I'm not familiar with the stock porting, nor do I know if you've modified it, but if I'm on the right track, you're operating too far down the slope to provide the best consistency.

 
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umair bhaur
(Login mubhaur)
YF12

No modification

August 9 2017, 4:42 AM 

has been done except that the gun is factory set for 879 fps with 18 grain jsb while I just increased the fps by adjusting hammer spring as you have advised.

 
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Jason
(Login nervoustrigger)
YF12

Next steps...

August 10 2017, 2:58 PM 

Hi Umair, sorry I haven't had the opportunity to reply until now. You said the velocity did increase when you added more hammer spring tension (preload) although you didn't say by how much. If you can get an increase of more than about 3% by giving it more and more preload (e.g. the nominal 895fps becomes 920+), things are not optimally balanced for a low ES. Here is how I would approach it...

Keep increasing preload until you find the max velocity, then back off until it falls to about 97% of that maximum. If the resulting velocity isn't what you want (either because it isn't accurate at that velocity or shot count is less than you want), you can either reduce the regulator setpoint and repeat this step until you get the velocity you want, or you can choke off the transfer port until you get the velocity you want.

With things adjusted this way, your tune is in a good position for achieving a low ES. But I agree with C. Jones' points about the pellets. A 1% ES is about as good as can be expected from a really good batch of pellets, and many will not be up to that standard. Even some batches of JSBs. And his other point about the hammer is good as well. Make sure it moves very freely and consistently. Deburr and smooth the tube, hammer, and sear and lubricate with a light oil (something in the 10W to 20W range) or run dry burnished with graphite.

 
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C. Jones
(Login limbshaker)
YF12

Pellets

August 9 2017, 8:36 AM 

I'd think that those 3 shots may be faster due to a slightly smaller pellet. Less friction/drag, means more speed.

Try sorting enough pellets to do a full string and see if it's any different.

Also, if you have never had your HW100 hammer apart, cleaning out the factory thick grease and relubing it with oil can help consistency. Especially in cold weather the grease will thicken and cause erratic velocity.

Since all the other shots look good except for 3, id blame the pellets first. Check them for bent or small skirts, and consistent weight, and head size.

 
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Jason
(Login nervoustrigger)
YF12

Umair, any luck?

August 15 2017, 11:58 AM 

Just curious if you have an update, even if it's just something you tried that did not improve things.

 
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