Two small data points.

In '08 or so, we converted an H&R 10 gauge single shot to .475. Firing pin was bushed, and a trigger job done, but that was about it for alterations to the action. The action never cracked, but the case head thrust quickly beat the standing breech concave. The rifle was retired after approximately 300 rounds.

About the same time, a friend converted another to shoot hot 45 Colt loads. I don't recall the exact loads used (could check, if needed) but I seem to recall thinking they were about the same as produced 1,300 fps w/300 gr. cast bullet in the 6-shot 45 Linebaugh I used to have. With over 1,000 rounds of this load, the rifle is doing fine.