I've never seen or confirmed a stretched frame, flex on the other in the action is common with max loads in high pressure chambering with larger case head rounds tho, I've personally tested a 300WSM barrel on a modern late model SB2 frame with no stretching of the frame, but the action does flex, mostly attributed to the weakness of the small pin supporting the latch IMO. Evidence of flex can be seen in the form of a few thousanths gap at the top of the barrel and standing breech(enought to see light thru) after the shot before opening the action, and hard to press release button.
The original owner of the 300WSM barrel shot ~100 rounds of factory ammo thru the barrel(rechambered 308Win) which resulted in the barrel being loose on the frame caused by underlug setback, the other barrel that was fitted to the frame still locked up tight. I bought the barrel for the cost of shipping to test it with start to midlevel loads of Accurate Magpro with the blessings of Johan at AA for pressures that may work on the Handi action. I did the underlug improvement to the barrel(FAQs) to avoid lug setback and worked up loads, but wasn't able to achieve even 150gr equivilent 30-06 velocities without the gap and degraded accuracy due to the large .555" case head of the WSM. The frame was never affected, other barrels still fit and worked fine on it.
Tim
