After several years in the safe, took HiPower to Range yesterday. Immediate FTFs. Slide was locking back after every shot as if mag was empty. Had to use slide release to load round after every shot. Then noticed magazine felt loose, not fully seated. Changed mag. Same problem. Both mags were not seating properly. When home, found another mag which seated much more securely. Don’t know if it will solve problem.
I didn’t have any mag problems when I last fired the pistol. It’s not a storage or maintenance issue. These were 13 rd mags. Don’t remember the make and they’re not marked. It looks like the mag that fit better that I found at home came with the gun.
Before I take it to gunsmith, any ideas?

As a supplement since posting this, I’ve read that this could also be a grip issue.  Thumbs-forward grip, which I use, can cause slide to lock back. Is this true?  

Anyway, I’ve ordered couple of new Mec-Gar 13 rd mags.

The mag that came with the pistol may be a Browning factory mag. (Which may be made by Mec-Gar) The problem mags may be aftermarket and could be the reason they don't seat/feed well.

New Mec-Gar mags arrived and fit like the others—a little loose. It must be high grip interfering with slide release. Will take new mags to range, but suspect it’s like Margaritaville—my own damn fault.