How do i know if i need the ar15 or ar10 version of this upper? — 4 Answers

This upper only fits a AR-15 lower only. You can use a AR-15 lower for 5.56, .223 Wylde, 300 blkout, 350 legend, 6.5 grendel, and 7.62x39 uppers. A AR-10 lower you can use a 308, 6.5 creedmor, 6.8 spl. uppers.

I was wrong about the 6.8 spl, you can use a AR-15 lower for this. You can also use a 450 bushmaster, 50 Beowolf on AR-15 lower. The AR-10 lower you can use 243, 7.62x51 upper also

I was wrong about the 6.8 spl, you can use a AR-15 lower for this. You can also use a 450 bushmaster, 50 Beowolf on AR-15 lower. The AR-10 lower you can use 243, 30-06 upper also