Your Mec-Gar mag may have a little heavier spring than what Beretta specifies in their OE mags. $25 for a spares kit with hammer & trigger and a spring you need anyway is just good insurance.
You may also want to check both the follower and feed lips of the Mec-Gar mag against your Beretta marked mags. They have goood quality control, but it's possible that the wrong follower was supplied, or (unlikely, but could still happen) that the feed lips are out of spec.
Of interest Mec-Gar is based in Italy and supplies, or has supplied, the OE mags to almost every major handgun maker. I had a NIB Ruger P95 in the shop tonight that shipped with the normal two mags; one of which left the factory with the follower in backwards. I of course had to disassemble it and reinsert the follower in the proper orientation. Things do slip thru at times.