I got mine late today, I have 2x mac10 made by Sam for a retired dealer close to me, I bought them both and also have PS one. I'm putting and leaving the upper on one of the Sam ones and gonna leave it on there..had to fit the lage upper to the Sam gun just a bit, the upper fit the PS just fine. I found on the Sam gun the piece of bar stock across dottom of rear to hold stock on was way higher and the lage upper would not pull down and pin on, some dremel and file to bottom of upper at the rear and it fits and pins on. I was thinking 3 years and over 3 grand and here I am dremeling on it. But turned out good, rear now fits snug and doesn't need those two set screws. And when it assembled can't tell it was filled on. Maybe get to shoot it next week