OK Thanks, That certainly makes sense.
Sorry about hijacking this thread.
Back to cosme9242 original question.
"Do you have to worry about headspace" ......on an AR.
My short answer is. Worry? No. Should you be concerned? Yes.

Maybe folks who have built their AR uppers can tell us:
1. Who has actually check headspace?
2. Who has actually found a problem?

OhShoot has already chimed in as finding a "problem".

I have built many ARs and you should ALWAYS headspace check.

I have had factory AR barrels from FN Herstal fail headspace checks due to the chamber being bored far too large.

always headspace check a new build. assuming ARs don't need headspace checks is just plain wrong.

It is cheaper to headspace check a build than it is to get facial and hand reconstructive surgery.

so to answer your questions:

1. I always headspace check AR builds.
2. I have found headspace problems on AR builds.