Re: steel vs brass cased ammunition, my experience (and opinion) has been that it depends on the cartridge and firearm. I've shot steel cased ammo in handguns, ARs, and AKs. Some others as well, but those are the main ones.
Handguns - I haven't had an issue shooting steel cased ammo in my handguns. Mostly Glocks and some others. No issues shooting Tula and I think Red Army or some other cheap stuff. All fine. No ill effects on parts wear, at least that I noticed.
ARs - It depends. The cheaper steel cases stuff like Tula seems underpowered and do not function well in my mid-length gas guns. They work well with my carbine gas guns. I bought a carbine upper from a known over-gassed company to test my theory on a wide range of steel ammo. Mostly because it was readily available and as times about 30% cheaper than say PMC Bronze or 193. Shortly after I got my test upper, both pricing and availability went to $hit.

That said, my shooting buddies and I have shot many hundreds (if not thousands) of rounds of Wolf, Tula, etc steel and assuming the right gun (gassing, chamber, etc), they've worked fine. One thing I personally do is after shooting steel, I'll clean the chamber really well prior to shooting brass.
AKs - I prefer steel over brass. I haven't shot brass AK ammo often, but when I did, I recall some problems. Not major though. It may have been a bad batch of ammo. We were shooting some donated brass cased factory ammo, and occasionally, the bullet would seemingly pull through the side of the case neck. Notices that occasionally when unloading a chambered round or when clearing the gun after a malfunction. Same gun and same mags followed with "known ok" steel cased ammo, no problems. I have some steel cased AK ammo (I think Winchester) that a buddy gave me. I'll do some testing.