this is extremely important to understand why some swear its trash, and mostly younger, or newer users dont, and its what makes the difference. For a long time the typical steel case stuff was loaded with a really light loading. Chronographing, they all ran around 2600-2700 FPS with the standard 55-62 grain bullets. Now pressure and velocity are not necessarily constant to each other, but its safe to assume that these rounds were loaded to lower pressure back then.
When you run 5.56 in a steel case, at low pressure, the case will not seal, and the soot will stick in the chamber. This causes cases to get stuck. The powder you find in these rounds if very dirty, and while dirty is not the problem people make it out to be, it can be if the dirt is acting like glue. Because the 5.56 is mostly straight, unlike the more common Soviet rounds, it drags its whole way out of the chamber. Laquer is not an issue, seal is not an issue. Just low pressure.
While I cannot prove this, I CAN say I have steel case that jammed specific rifles badly, and pulling the bullet, replacing the powder with a better suited powder, of normal pressure, reseating the bullet, so in effect changing nothing but the pressure, this rounds shot and cycled just fine.
What is important now, for a decade now, most steel case has been loaded to higher velocity, last run I chrono'd hit almost 3K, so, again presumably, loaded to a higher pressure. This stuff runs fine.
Steel case often equals steel bullet. Steel is always going to wear more. In an AR where the savings outweigh the barrel replacement its not really a concern. In a rifle without cheap easily changed barrels, I would avoid it.
My personal observation has been that SAAMI .223 Rem chambers stick less than 5.56.
