steel ammo (no, I'm not kidding) and shoot it about 95% of the time when I'm shooting... I shoot silver/brown bear, wolf, combloc surplus, ect... The only
ammo I've ever had issues with is Herters. It was insanely dirty and didn't function properly in my Glocks and AKs (if those guns can't run it, nothing can
). So I stay away from it nowadays.
Now as far as shooting steel cased ammo in your ARs----I'd bet at least 75% of the issues people report on the internet are caused by mixing brass and steel without cleaning in between. The steel cases don't expand like the brass does allowing fowling issues that can cause issues when brass ammo is introduced into the mix. If you shy away from that you'll likely be okay (generally speaking).