I'm not sure I see what the advantage of an AR15 platform chambered in .30 carbine would be over a well maintained M1carbine. Starting in the late '90's I carried a M1 carbine in my patrol car as a deputy sheriff for about 10 years. I had to qualify with it a couple of times a year standing next to other officers shooting black guns and the only real handicap to the M1 carbine was the cost of .30 carbine ammo compared to .223.