what caliber uppers fit a 5.56 lower

what caliber uppers fit a 5.56 lower. There are some references to what caliber uppers fit a 5.56 lower in this article. If you are looking for what caliber uppers fit a 5.56 lower you've came to the right place. We have posts about what caliber uppers fit a 5.56 lower. You can check it out below.