Are all the 55gr and lighter projectiles giving you large ES/SD numbers ?
It could be that you are seating the light pills further from the lands, so more time in the freebore giving you inconsistent pressure ? Not something I have a lot of experience with, one of the other guys might have some ideas on this.
I wouldn't expect twist to give you poor ES, more likely poor group sizes. Not like you are using a slow power. I use BM2 for 55/62/69gr in the 223.
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