Thank You everyone for your responses. I think an upgrade to Impact MK 3 is probably the thing to do!
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Thank you for all the great information.First off, I want to apologize, because I started this thread, and I didn't follow up with another post after my last post on March 24, 2022. I think I just got involved in tuning, and forgot.
My last post mentioned I had an increase of 17-19 fps by just changing to the new high flow pin probe, but I never gave my results after I installed the new Huma-Air hammer spring.
Without changing regulator pressure of 145 bar and hammer spring still at A, my velocity went to 883 fps, for an increase of 11 fps. My ES increased to 13, but I was still getting a group of 3/8" at 57 yd.
I then went to hammer Max for a velocity of 890 fps and ES 10.
My final adjustment was setting my regulator to 150 bar and hammer to Max, for a velocity of 894 fps, ES 10 and 3/4" group.
That's the most velocity I was able to achieve, and didn't want to go any higher with my regulator.
Since then, I have installed a new Superior Heavy liner and carbon sleeve. I had hopes that with the faster twist I could increase my accuracy with slugs, especially at lower reg pressure and velocity. Unfortunately that didn't happen for me. My .25 33.5 gn NSA slugs seemed to have worse groups.
To my surprise my JSB Hedes pellets were shooting very good groups. Almost always under 1" at 57 yd, and *I even had a 100 yd group of 1 5/16" with 4 or 5 shots 5/8" c-c This was with 120 bar reg pressure.
Once the weather starts getting better, I have some H&N Slug HP's I will bi trying. I had some good initial results with the .250 32 gn slugs, and will also be trying the .250 30 gn slugs next.