A month or so back I did some calculations and posted them. The SB1 frame is the same for a .410 thru 12 gauge, so this should give you an idea of the loads on the frame. Larry
30-30 42,000psi gives 5,871 pounds trying to push the action open.
45-70 28,000psi gives 5,605 pounds
.223 55,000psi gives 6,039 pounds
12 gauge 11,500psi gives 5,748 pounds
30-06 60,000psi gives 10,519 pounds