I know very little about this upper, but I will do my best to describe what I do know. This is a SaberCo Inc. 224 AR upper with a 26" bbl.. This was a project my father was working on before he passed last fall. To my knowledge, the 224 AR uses 6.5 Grendel brass necked down to .224. I say this because I did find some shells he loaded for this upper. This is NOT a 224 Valkyrie, which uses 6.8 SPC brass. I found some paperwork last fall, for when he purchased this, and naturally I have since misplaced it. I am open to offers. I have a good idea what it is worth, but I know it is only worth the correct amount for the right person. Price is negotiable. Please make an offer if you are seriously interested. Message through Nex-tech or text seven eight five three two four 2 2 six three.