My 6 cavity drops right at .430 - .431 with COWWs +2% tin or range lead with 2% tin + 30% lead added. I size at .430 and they shoot just fine in my 2 Rugers (44 Mag and 44-40), Colt Anaconda, Hawes Western Marshal and Contender. Might try adding 2% tin to your alloy and see if they don't come out a tudge larger.

Larry Gibson