As another thought. I shoot a 54 cal with a 1/60 twist which is designed for the RB,which it shoots quite well. But it also shoots the Lee 300gr REAL bullet with great accuracy. From the picture you see the Lee bullet is very short. Slightly longer than the RB. I believe a short conical like this might be an answer to your accuracy problem. In my rifle I shoot Triple 7 FF, 100grs. If you were to start at 60grs , then go to 70,80 & then 90. you most likely will find a sweet spot for accuracy in your rifle.
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