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I haven't been able to get good subsonic accuracy with the Hornady 220 round nose in my Whisper or my 308. Both of them are 1:8 twist barrels. I wouldn't think that a 1:10 twist would make their accuracy any better. Yes they are shorter but the driving area or something does not seem to like the slow speed or lower pressures. This Saturday I decided to give up on them after repeated testing in my Whisper (I was only getting 3 to 4 inch 100 yard groups). Sierra makes a heavy round nose bullet also but I haven't tried it yet.
I don't know the exact volume percent that 5744 and 4759 gives me in a 308 size case. I would guess that it is about 1/3 to 2/5 of the case or so. It is substantially more than the fast pistol powders.
Some powders are more position sensitive in the case than others when lower volume charges are used. Tipping the barrel down or up before chronographing your loads will tell you this. The fast pistol powders, in my experience, seem to suffer from this more than 5744 and 4759 do.
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