[Nugget]

*** See post #3 for solution ***

2014 box label date; two mags that came with the gun drop free when loaded and slide open. These are ".45" marked (missing "ACP" lettering). Supposedly, they are the older iteration with fatter floor plates and a slightly higher cutout.

Fast forward... Ordered eight new mags marked ".45 ACP". Newer iteration with thinner floor plates and very slightly lower release cutout. Now, if I have even one round loaded and the slide open, they won't drop free.

Anyone else with this problem? There were some brief mentions in some posts (like here), but it obviously doesn't seem like a wide-spread issue, and the post seems to describe exactly the opposite of my experience. I'm most likely going to let it be, because I don't foresee myself getting into a situation where I would need to drop a loaded mag with the slide open. Just wanted to share.

 

[Willard]

Nugget, first off the old magazines are more than likely Mec-Gar manufactured, as they are marked as made in Italy. The new magazines are more than likely Checkmates, and are American made.
The next question I would ask, is grips... are these E2 grips, or screwed on?
If screwed on, remove screws, and see if problem persists, and likewise, if E2 grips, remove them, and see if problem persists. If not, then there is some interference, either between screws length, or threaded inserts for the screwed on grips, or the locking projections of the E2 grips, and magazines.

 

[Nugget]

Nugget, first off the old magazines are more than likely Mec-Gar manufactured, as they are marked as made in Italy. The new magazines are more than likely Checkmates, and are American made.
The next question I would ask, is grips... are these E2 grips, or screwed on?
If screwed on, remove screws, and see if problem persists, and likewise, if E2 grips, remove them, and see if problem persists. If not, then there is some interference, either between screws length, or threaded inserts for the screwed on grips, or the locking projections of the E2 grips, and magazines.

They are Mec-Gar Italian mags as well, but your line of thinking got me considering the grips. Turns out, the Hogue G10 grips are molded after the older, taller floor plates. The new floor plates are thin enough to ride under the the "steps" I've outlined in the photo, where it would grab hold. I spent about 45 minutes slowly sanding down the steps while listening to a podcast, and the mags now drop free. So everything ended up hunky dory.

 

[Willard]

I'm glad you got the problem solved, and if I can remember, it may help out the next individual that has the same problem.
I'm also glad you responded on how you cured the problem... too many times we never hear if the problem was resolved or not.