I have the same issue with my new M9-A1 - it came with the 17 round PLUS mags.
Since I am not going to clean mine until I put 1,000 rounds thru it (little experiment), I suspect I will continue to have this problem. When I get done with my testing I will look into this further. There must be some way to slick up the grip frame. I do not think the mags are the issue. My mag release button is also very tight and it takes some force to overcome the spring tension.
it is not an issue of making anything smooth or oiled. the magazine release is shaped to not drop free. use a round hobby file to trim the front of the mag release ( forward of the part of the release the holds the mag in. )
slowly take material away. you don't want to trim the back catch part....but rather u want the ledge hollowed out more...this is the part that rubs against the mag body...using friction to keep it from dropping.
Mine always dropped free. Then again, I either give the gun a quick downwards bounce when I press the mag release, or a quick "flip" motion to the side that propels the mag across the room with significant authority. I'm sure if I were to just press the button and hold the gun still I'd get the occasional sticky mag.
Could you repost or link the photo showing the 'part u need to file using a round file?' It seems the photo is no longer there.
In any case, my experience is that normally, the magazines drop free. I've shot this think a good bit in the last half a year or so since I bought it; around 5k rounds; enough to satisfy myself it is reliable with my chosen defensive ammo, etc.
I've dropped these magazines issue free on all kinds of stuff during practice; never wet dirt, however. It's when you get the magazines dirty by droping them on wet dirt is when they begin to stick. My l9 came with two 17rd mags that seem to have a nitraded finish. These dont stick as much under these circumstances. The blued 15rd mags I purchased do stick consistently; all 8 of them. All the mags are good quality. No issue there.
On a side note, I'd like to modify the stock rear site so that I can rack the slide one-handed of my belt. I'm considering a protruding set screw. I like the stock trap sites. They work for me. Any thoughts?