I have one of Oly Arms .45 ACP AR carbines. I bought it back before Glock mag lowers were popular (I don't think I had even seen one on the market yet) and the only other option was a submachine gun magazine conversion with a custom upper. It works well and was an excellent choice for a complete kit given the other options at the time. It fits on an M16 lower since the magazines fit the standard AR mag-well, which is cool. I just with they offered larger capacity magazines for it.