Make sure your thumb or off hand is not making contact with the slide stop/release, I have a bad habit of making contact with it which prevents it from engaging.
My XDm's slide will not stay locked in the open postion when the last round has been fired. Can anybody explain to me what the problem might be???????????
That doesn't seem to be the issue. Any other ideas?
Yes, it fails to lock with both the magazines. It also will stay locked when operated by hand. This is the only handgun I own so I am not sure if it feels stiff or not........
If oiling fixes the problem, I would take the gun back down and wipe off any excessive oil and then apply proper (very limited) amount of gun lube to proper interior slide and other surfaces.
P.S. - Might want to also apply some Rem-Oil to your magazines.