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The reason we use brass in the first place is because it's malleable. This means that as it is being fired, it easily swells up and seals the chamber. Most of the reason steel runs dirtier is that it doesn't do that as well.
Obturation. The process of the casing expanding inside the chamber and creating a seal is called obturation. You are correct by the way.
To expand on this: there are reasons to or not to use steel cased ammunition. In a "commie gun", the chambers are actually cut smaller than western chambers. That's why any AK you pick up will not headspace correctly with headspace guages.
Go gauge won't go. A live round - or a dummy will though.
The commie guns are made to use steel cased ammo: steel expands LESS than brass, so to counteract that they cut their chambers smaller. Technically this could cause excess chamber pressure if you threw in a brass cartridge which wants to expand more against a tight chamber wall but commie calibers aren't high pressure.
So in commie guns steel ammo works just fine. In western guns which have chambers cut for brass ammo: steel causes problems in two ways.
1. Because steel casings obturate less, they won't seal the chamber as well during ignition.
This is what has given rise to the myth about lacquer coated casings dirtying chambers. the idea being that the lacquer or zinc flakes or melts off onto the chamber walls gunking up your chamber. Trust me: you can't melt that **** off the casings without a torch and by the time you get it to start melting - so does the brass.
This is a myth, flat out. The reason the chamber is getting dirty as hell is because the steel casings, in a chamber not cut specifically FOR steel casings: doesn't completely seal the chamber. So there's a lot of excess carbon build up because the chamber isn't sealed.
2. Steel has less natural lubricity than brass and if often not polished as well as brass casings.
Steel, unless carefully polished: isn't as smooth as brass. It never is, actually. Brass and steel polished to the same degree have different levels of lubricity and surface resistance. There's a reason polishing the chamber improves function: it decreases resistance to a cartridge entering the chamber and resistance of a cartridge being removed from the chamber.
Well: if you have a smooth chamber but feed it fairly rough surfaced ammunition - it's just the same as if you had smooth ammo and a rough chamber.
When you combine dirtier burning comblock powder, with rougher casings and create undue chamber fouling due to a pour chamber seal during ignition: you have a recipe for malfunctions.
The weird thing is: 2 types of guns work really well with steel cased ammo.
Cheapo comblock guns made to use steel cased ammo and guns with exceptionally tight and ridiculously smooth chambers. These guns are usually very expensive.
In general, steel ammo will work just fine. You'll just have to clean your guns a lot more often to adjust for the fact that the chamber will foul much faster.
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