It Varies
Mas shoots a variety of stuff.
When I spoke to him last year, he mentioned Glock as a routine carry.
Seriously, though, you can put just about anything in his hand and he'll hit inner rings with it.
I had the pleasure of spending an hour or so with one of the people he's personally trained, and who is one of his trainers for the LFI course series. Bob Smith. Good guy. Also runs the mixed use range near here.
I watched Bob and Mas train shooters for most of day one on the LFI course (got some pix), and watched both of them, when necessary, take pistols the students were using and demonstrate technique. Didn't seem to matter what the gun was, Mas and Bob seemed right at home.
Later, I did a little shooting of my own. I was having trouble staying in the rings. Bob came over and watched for a bit. I handed him my pistol -- one he'd never seen or fired before -- a Taurus PT911 (9mm), and he proceeded to put almost all of a magazine into a two-inch circle at 15-20 yards, off-hand.
Well, okay, it clearly wasn't the gun.
My point is that, when you shoot enough, when you practice enough, when you achieve mastery of the art, you can use darn near anything and get the hits.
When it all goes down, I want him on my side. I know I can toss him whatever's in the bag and he'll be just fine.
. Sorry to get off topic 
