I've been following this post and I looked through all 6 uppers I have, and my buddies rifles. We checked rifles made by: bushmaster; colt; Olympic arms; SGW; Palmetto arms; Armalite;and Eagle arms. I have yet to find an upper receiver without the auto sear cut out on the bottem of the upper receiver just forward of the rear hinge pin block. I think all the forged upper receivers are machined to M16 specs. You can see the cut out illustrated clearly in the P.O.F. add for their CROS fininish on the inside of their receivers (the back of the July 20 shotgun news has a full page color add). I understand the bolt carriers are different between an M15 and AR15, but aren't we talking about the actual aluminum upper receiver here? If someone has a picture of an AR15 without the auto sear cutout on the UPPER RECEIVER please post a picture of it.