Rock River Arms has introduced an AR-15 in 7.62x39 that uses standard AK-47 mags. It should be available in 60-90 days, according to RRA. The bore has a 1/10 twist and is chrome lined. The upper itself was clearanced for AK mags, something those who are interested only in the lower should keep in mind.
This was of particular interest to me because I shoot a lot of 5.45x39 through AR-15s, and while my own magazines are reliable, 5.45x39 AR-15 magazines as a whole are not. The Rock River Arms folks said that the lower should work with 5.45 AK mags, but they have no plans to introduce a 5.45 version, nor do they plan to sell the lower separately.
The mag release was pretty wide and easy to access from both sides, and the mags locked into place fairly well. MSRP is over $1,400, and it will be interesting to see what demand is like for this product.
