Steel cased ammo works fine in the AR . Couple things to consider
So I've been doing a little research on the steel case vs brass . What I found out is that steel case ammo does not expand as much as brass . That means at times the steel cases do not expand and seal the chamber completely . When this happens gases and crap can get blown back into the chamber and carbon can start to build up . If your only shooting steel ammo you should be fine cus with the lacquer and other finishes they should still be slick as snott and cycle fine .
I also here if your shooting alot of steel ammo in the same day you do not want to switch to brass . ( first few mags steel then immediately switch to a mag with brass )The reason is the carbon and or burnt lacquer or other finishes that may have built up in the hot chamber can cause the brass cartridge to adhere to chamber wall and fail to extract and that can destroy an extractor or rip the rim off the case .
So only shoot one or the other per trip or per cleaning and always clean your chamber really well after shooting steel cased ammo . If you do not clean the chamber really well after shooting steel ammo the carbon can continue to build up and create problems with all ammo being shot thru the gun .
here is the link http://www.theboxotruth.com/docs/edu18.htm
It makes sence to me . Im not sure if there is any science behind it but thats the way im going to do it
If your going to be shooting alot of steel cased ammo I would keep some extra parts with you at the range and really all the time . I don't shoot much steel but I always have this with me http://palmettostatearmory.com/index...rer-s-kit.html