I have an extra lower sitting around. I wanted something with a little more punch than my 5.56, so I was thinking about buying a 300 blk upper to put on it. I looked at the price of ammo and no way I could afford to shoot it much without taking up reloading. Model 1 has 7.62x39 uppers at a real reasonable price. That would let me shoot cheaper ammo and still have a round with comparable ballistics to the 300 blk. Does anyone have any experience with the AR platform in 7.62x39?