A logical question to ask is, why do this? After all, we have other options for AR-15-sized uppers to fire .30-caliber rounds—the .300 Blackout and .30 Rem. AR to name two—and those rounds have designs that allow them to feed through standard AR magazines. The 7.62x39, in contrast, is inexorably linked with the iconic banana-shaped magazine that will not work in a standard AR lower. This means a gunmaker needs to build a dedicated lower to make a 7.62x39 AR run, and that, in turn, jacks up the price.