A weak spring in the slide stop is what first leaps to mind for me.
A misshapen magazine follower could also be a culprit; did this happen to him with every magazine, or only with certain magazines?
I've never had that pin come loose on a 1911, and have never heard of such, but I suppose any mechanical part can fail.
He only had the one magazine with him, so we couldn't do a comparison.
I did look at the follower, it didn't look damaged. It would push the slide stop up about between 1/2 & 1/3 of the way, but it was not enough to engage the notch in the slide 100% of the time.
I didn't see a spring at all on the slide stop. Where is it supposed to be located? That was one of the 1st things that I thought about, based on my experience with the Glock and installing the slide stop spring wrong and causing premature lock open. But after he took it apart, I didn't even see a spring.
So that little pin should be staked in place?
That is what I told him, but he said I was wrong. I told him I didn't remember it ever being loose on the old 1911 I used to have.
So will he need a new barrel assembly or can he get a pin an stake it in place himself?