Interesting, just took a look at it and the rim is noticeably smaller. I don't have an AR but just tried loading 3 rounds into a PMAG and manually cycling them through my Sig 556, all chambered and ejected with no problems. Also pulled the bolt partway back and tried to get the round to come loose from the extractor without success. Of course the regular extraction sequence is a more violent but it looks good so far.
Did some searching and it looks like chamber pressure is only 15,750 psi which gives the 3.6gr projectile 4,525 fps muzzle velocity.