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August 10 2017 at 2:58 PM
Jason  (Login nervoustrigger)

Response to No modification

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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