I've shot a 300WSM barrel on a modern SB2 frame with no change to the frame, but frames older then '99 are subject to frame damage due to them not being heat treated to the same strength as current production, and the reason H&R won't fit high pressure barrels to them.
But current frames will flex which was evident after shooting mid level loads in the 300WSM, there would be a noticable gap, probably ~.005", between the barrel and frame after the shot, before the brass was ejected. Case head thrust would flex the frame enough that after the pressure released, the brass had expanded to the rear enough to not completely go back into the chamber causing the gap. Surprisingly, the brass did eject fine, which usually sticks when that happens in standard chambered H&R when hot loads are encountered.
I suspect that extended shooting of hot loads would likely cause the frame to fail eventually due to metal fatigue, although no one has ever reported that. The previous owner shot about 100 rounds thru the 300WSM, some factory loads, and the rest handloads during load work. The frame was not damaged and other barrels that were originally fitted to that frame still fit fine.
But the underlug was set back and was loose on his frame, and it wouldn't lock up tight on any of my frames, and I have a lot!! I improved the underlug to eliminate that issue, and it worked, see Underlug Improvement in the FAQs. That underlug is at my gunsmith's shop now for welding to a Shilen match 6.5mm blank to become a 6.5x55 custom Ultra.
The frame that I shot about 50 rounds of the 300WSM showed no apparent damage and the original barrel still locks up good on it. So, in my experience with modern frames, they flex with hot high pressure loads, but I've not experienced any change or damage. That's not to say that extended use at high pressures isn't going to cause a problem sooner or later.
Tim
