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170 grain 308 subsonic trailboss12/8/2023 ![]() ![]() On my Savage 10 FLP bolt action, on which I put a 338 Federal 18" heavy barrel to shoot primarily 300 grain subsonics, I put a 30 MOA scope base on it. So your gunsmith friend is right: 30 MOA base needed to reach out and touch something subsonic at longer ranges. It would be better to have a 30 MOA base to get almost the total range of scope adjustment. On my DPMS LR308B with 18" barrel I have a zero MOA base but use a tactical mildot scope with ~100 MOA total adjustment. Here is the calculated ballistic table for 220 SMK at 1060 fps using BC=.608. It could be a little more, I don't have my notes handy. With my 18" barrel, I think there was something like 10" adjustment up to have a hundred yard zero versus 200 yard for supersonic. What kind of hold over/drop are you getting with your 220s at varying ranges? My gunsmith friend was wondering if we needed to build some angle to the scope base. There was a big difference in supersonic vs subsonic drop. I'll want to shoot the load suppressed to "get an ear" on it. I don't think any cracked, but I can't be completely sure since I was inside and behind the shooter. We were shooting out of a heated shop so my numbers probably aren't applicable for your question about temperature. There seemed to be a lot of variation, but with only 5 rounds I doubt there's anything statistically significant. I only shot 5 rounds with each loading, but it was the loading that kept me above 1000 and below 1100. The magic number with this particular rilfe seemed to be 14 grains of Trailboss(20 inch 1/10 shilen barrel).
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