Yeah, but I don't know of anyone who ahs gotten the mags to hold more than 18+1 in .40. With 20+1 being the gold standard, that could be a bit of a disadvantage on 19-21 round stages.
So far i know jester made some out of plastic.. got 18+1 for 140mm IIRC.
novak handgunners outlet did some.. got 18+1..
Then there is that other guy who makes the base pads that I'm totally blanking on. Makes them for glocks and CZs where the retaining mechanism is an aluminum plate you screw on the back. Can't remember the name. Heard rumors he was working on ones for M&Ps. No idea on capacity.