Ah--in other words the thinner tip broke at a shoulder where the pin gets wider? I'm thinking it has to be striking some interference with the bolt; the pin is just along for the ride inside the bolt. It occurs to me another possibility is that there might be a side load on the pin head if it's protruding too far out while the case is being ejected; But I would suspect you'd see something on the the brass/primers as evidence.
