Great Article from Andrew on steel vs brass.
http://www.luckygunner.com/labs/brass-vs-steel-cased-ammo/
One thing to note is 2/4 carbines had to be taken apart and reassembled due to loose barrel nuts(go bushmaster).
This is a duplicate thread. It’s posted somewhere else here too.
It’s in general discussion.
It most certainly is not in GD.
It’s in AR GD.