So here's my review: Get the big harbor freight die grinder, I think it has a low and high speed switch on it. I've had mine forever, I bought a red rock or two at HF to go with it. Like he told me, I put the adaptor on, tried to insert a mag, and clearanced where it needed to fit like the original mag. I think it took an hour or two. I'm sure a mill would produce a better result, but what can you do. I used some dyekem to see that I was getting even surface engagement by the mags(OK, I used rustoleum) to try and make it nice and flat, but meh I just did O K .
Final product: I tried a dozen old AR mags I've had forever(with new followers) and all of them worked flawlessly. I put the mag in, and have to give it a little slap to make it snap in to the catch. I could probably remove more and would be able to put it right in, but the mags fit snug with about as much wobble as the originals, so why mess with something that works, I figure.
I don't think its very likely the trunion will crack. I guess anything could happen, but then that applies to everything. Nothing ventured nothing gained.
I went from a rifle that had two mags that cost me $49 each, to a rifle that has a dozen mags that cost me $8 each. Much more practical! The release works great, drops the mag free, fits tight, what's not to like?
Thanks Renegadebuck! My only complaint is I really had to track you down from other forums. I'll do my part to help by posting my review on Calguns. Thanks again!