I am building an AR, and have a question. I've heard that you can buy different caliber uppers for the AR. my question is, what caliber uppers can you mount on a basic (.223) lower? I hope this makes sense.
You can mount almost any caliber - 6.8, 7.62x39, 9 mm, 5.45, - as long as you have the appropriate magazine/adapter and sometimes you will need to swap the recoil/ buffer.
