When a primer is pierced, the rapid occurrence of breechblock damage is from one thing only, and that is escaping high pressure gas going back, and going up! One has to remember, the breech is locked during the first few milliseconds after firing. The only mechanical movement is inertially back, with the complete top end involved, the damage is most likely done before the receiver ever even starts to move... I have seen this progression to failure with my own eyes, and three shots is about the max you get... correct the headspace issue, and the problem goes away! I am so paranoid about this that I always make sure the toggle train closes tight on the "GO" gauge, (yes, you need both gauges!) when installing new or old original barrels. Excessive head spacing can be a result, or combination of the following. Breechblock at one end or the other in tolerance, barrel chambered too deep, wear on any or all of the three main toggle train pins. It adds up fast! Good luck to all when shooting a loose gun!
... best to all, til.....lat'r....GT...
