KAC / LMT are the same lower forgings. The Larue is billet, and might have a bit tighter tolerance , you would need to file down the upper in the rear and the pin size might also be different.

Quote Originally Posted by tom12.7 View Post
I've tried swapping uppers and lowers on a few. The KAC and LMT swaps went well. Either with Larue looked real close, but it would've taken more force to put together than what I was comfortable with.