Just because some conversions were done does not mean they were either practical or advisable. In most cases, the problem will not be a sudden "blow up" but rather a battering and pounding over time that will eventually destroy the gun or create a condition, like excess headspace, that will lead to destruction. So gunsmiths could do a conversion, test fire the gun, and the customer might use it for hunting for a long time, firing two or three shots a year. But eventually trouble will come looking for a place to happen.
Those looking at older guns sometimes misunderstand case hardening of breech blocks, locking lugs, etc. Case hardening does a good job of reducing/preventing wear from the friction of moving parts. But it does NOT prevent the battering of parts, like locking lugs, which still have a soft inner core under the case hardening.