I have no trouble running steel case ammo through my AKM, the SKS, the CZ-52 or the PPS-43. All those Warsaw Pact refugees were built to run on the stuff. Steel is cheaper than brass, a fact that was clear even in WW2, as those who have shot any FA 42 loaded .45 ACP can attest. That it may not be suitable for all guns is also true, as the Germans marked most steel cased 9mm as "not for use in the P-08."

But have also seen these markings on steel cased 9mm ammo boxes which did not prohibit use in the P-08.

"Pistolenpatronen 08 m. E
1944 am 16
Nz.Stb. P n/A. (0,8 . 0,8) . 1944 mog 3
Patrh. (St) Lack. 1944 am - Gesch. 1944 am
Zdh. 08 - 1942 faa 31"

All that ammo worked great. The problems seem to come from whatever coatings are used to keep the steel cases from rusting. Green lacquer goes back decades. Clear polymers are the current rage. I find the red lacquer the Russians use to seal the primers particularly nasty to clean off bolt faces.

The propellants used by the old Warsaw Pact countries have a distinctive smell. It immediately takes me back to the days when I was shooting more in earnest. I remember being surprised when some ammo I had loaded for my M1 gave forth "the smell." After I got home, I looked at the can of Accurate powder I had used in those loads and discovered the label said, "Made in the Czech Republic."