Though I haven't seen any additions to this post, I thought I'd add some additional observations. I actually sent my XDM in to SA, partially, to report this very problem. In my last range visit just prior to sending in my gun, I had about 6/7 failures to lock open. However, even as I was packing my gun to ship, it occurred to me to try simply manually racking the slide back on each of my 5 empty, 19 rd magazines. I repeated this at least 10 times on each magazine. I could not make it fail to lock back! In my previous post, I mentioned 4 possible explanations for this malfunction. While speaking with SA about it, I realized a fifth, almost obvious, explanation: sub optimal ammo. The only type of ammo I have ever fired in this gun is the 115 gr. target ammo. I have used several manufacturer's products, by now, but all were 115 gr. bullets. (I usually buy what I can pick up for the lowest price, at the time.) In contrast, SA typically uses a 124 gr. round for their testing. Could a heavier, hotter round simply fling the slide back harder & farther? Likely so. That said, SA, after our discussion about bullet weight, went so far as to acquire some 115 gr. test rounds. Yet they were unable to get a single failure to lock the slide back on empty. In short, they found nothing about my gun that required repair. Interestingly, I've had the gun back on the range one time since I got it back from SA. I fired about 6 magazines (of the usual 115 gr. El Cheapos) through it, and I only had 1/6 malfunctions of this type. Before: 6/7. After: 1/6. That's a big difference, but it also shows that it is still going to happen--at least with this shooter. Was I thumbing the slide lock lever? Maybe--I've got a hard focus on the front sight. I'm unable to know what my thumb is doing while my concentration is elsewhere. I am not accustomed to quoting Mr. Occam, but thumbing still seems to be the best explanation for this phenomenon, if only by an iota.
