Okay so I'm looking at the retailers and the companies website/store... and it's basically giving me two options. the Gen 123 or Gen 4. I'm not going to buy it right now but the Gen 4 model claims to only work when in Short Frame Configuration. Do you have the Gen 123 model using the M Backstrap then?
Yep, the 123 model. Only go with the gen 4 version if you prefer the smallest grip option on the gen 4 gun. I tried that method with the 123 model and it worked also, but one could say that it wasn't on their especially tight. If you end up getting it and have trouble getting it on, I have a good video for it. Basically says to put on the medium grip, put the extended pin through it, then hook the beavertail on one end, and snap it onto the other side. I tried pushing them onto the gun and putting the pin through for more than an hour before seeing the video, which made it work instantly.
Buddy offered me 100 bucks and his CMMG lower for my RRA lower. should i do it?
His complete lower for complete lower? If so, I don't see why not (provided it got the same furniture as yours,etc). Lowers themselves aren't as critical as uppers, so they should be all pretty much the same. I don't remember if CMMG used a milspec receiver extension though, but i know RRA doesn't.