I wanted an AR with a little more "OOMPH" to it and my choices were 7.62x39,6.8 SPC and 300 AAC. Of those 3 I picked the 300 and as to why the 7.62x39 doesn't work well in the AR platform. The 6.8 SPC bullet choice is somewhat limited and living in Ma I'm limited to 10 rd mags. The 300 uses standard AR mgas,can use bullet weights from 100-250 grs and brass can be made from 223 cases. If I ever move out of Ma I might give the 6.8 SPC a try.