I finally bought my lower for my very first AR build. i'm a really big AK(or ak variant) guy but i have been wondering what caliber should i choose to build for my ar. i like the 5.56/.223 but i have seen uppers that are chambered for the 7.62x39. i like the accuracy of the ar platform but i like the knock down power of the ak.......does anyone have, heard, or seen this setup and know enough about it to provide pros and cons about it? all feedback welcome.