BTW, I didn't mention how it didn't fit...you could put it on the muzzle brake, but even if you tightened it all the way it wasn't snug...needed to go in another 1.0 - 1.5mm.
Fixed it by removing the roll-pin, and used pliers to tighten it the last little bit. Works great!
Also, had to do a little digging to make sure I had the right blanks. The blanks I have are black on the tip, not violet, which is supposedly the color for M200 blank ammo (according to many, many websites). However, TM 43-0001-27 (Army ammo specs) has no color specified for M200 blanks, just a narrow strip of knurling 1/2" from the cartridge-head, which mine does have.