I've been in the process of building 3 ARs, I have the lowers pretty much completed, now I just have to decide on the uppers.
Since I already have 3 in 5.56 (along with a .22 conversion kit), my initial thought was to build:
1. 7.62X39
2. 300 BO
3. 9mm
But then I thought it would be nice to...