I got a couple of thousand rounds of full house .357 Max through one of the old H&R shotgun actions. That's operating at about 50,000 CUP. Ain't nothing stretched or loosened about it. Nothing worn, neither, and I have a good 10,000 rounds of .38 Special loads through it, too.
If the old soft mallable iron frame will take that, the heat treated SB-2 frame will take far more. All you really have to do to discount the hinge pin loosening story, is to pull off a barrel and look. The hinge pin is fully supported across its entire front, not just at the ends.