You would run steel 5.45 and 7.62 through this upper but not 5.56? Why? If you said you didn't run steel period that would be one thing, but you obviously don't have a problem running steel...
When I had my RLL host in 5.45 & 7.62 ran ok after m60 Joe worked on chambers. 5.56 would not run with out sticking bad only ran brass case 5.56.
Never run brass after Steel case without cleaning. Only problems were broken extractors. No other problems found after many cases of steel case ammo.
7.62 needed a different firing pin for reliable bang & never fed reliably in the ar platform.
7.62 Sucked in f/a beet shooter & gun bad .
Just my 2 cents after a lot of money spent trying to make it work