[QUOTE=EthanG-M&P;135892217]

I am not a fan of forcing things I paid too much money for. I was told by some gun dealers (who own the M&P 9mm), that it is strictly a 10 round pistol, and I am not going to force it to be otherwise. Just saying... You may do as you please. If it works for you, it works.
[QUOTE]

In case you haven't discovered this yet, most gun salesmen are gun SALESMEN, not GUN salesmen. Half of them couldn't find their own ******* with both hands, a flashlight, and a ****ing map. Listen to them, smile, nod, and then do your own research.

Your gun is designed to hold 10+1. Everyone I see shooting an M&P is running them 10+1. I've put several thousand rounds through my M&Ps with 10+1. If you want to get it straight from the horse's mouth, you can call S&W at 1-800-331-0852 and they'll confirm that you can run 10+1 (even with the castrated MA mags) without damaging the gun.

I know of several competition shooters that have filed down the BOTTOM of the follower in their M&P mags to make tac reloads easier. Personally I haven't bothered.

It sounds like most of your original questions have been answered, though I want to point out that in order for a civilian to legally have a magazine in MA that holds 11 or more rounds, the magazine needs to have been made before September 13 1994, not 1999 (in addition to you having a LTC-B for rifle mags or a LTC-A for pistol mags).