The 50 Beowulf the the new 50 cal. upper for an ar-15 platform, made by alexander arms. Just swap your convention .223 upper with this beast of a weapon and ....poof. 50 cal. power almost instantly. Pretty cool. i am enjoying mine very much.
check out this forum for a small video of it if you are interested in learning more about it.. think its about a 10 min video. 50beowulf.com