the 458x1.5 Barnes is one I was going to build, made from belted mag cases cut down to 1.5". I put a hold on the reamer after I heard about the 450 bushmaster.
Tony Romix built several aks in 458 socom I posted those sites a couple years ago I heard the pics are not there anymore. I emailed Tony about the builds they were done on milled recivers and used standard AK bolts and other parts. there is a thread here some were. there is a 500 phantom and a levithan round that is pretty big as well. the socom and beowulf are classifed as pistol rounds by the way.