A 1 in 12 twist should stabilize bullets up to 55 grains. Sometimes there are bullets that won't stabilize when others will. Sierra Blitz Kings in 55 gr. need more twist to stabilize than other bullets of the same weight. 22-250's with 1 in 14 twist are very popular. They will shoot bullets up to 55 gr well. Sometimes they won't shoot the heavier ones very accurately.