I shot alot of steel cased stuff when I first got my AR. My rifle ate it just fine but you just gotta make sure you clean your chamber well. The only problems I had happened when I switched from steel to brass in the same session/range trip. the brass kept getting stuck in the chamber, i guess from the laquer shit that's on the steel cased stuff melted off and caked up the chamber. i don't really know for sure, but I stopped shooting steel cased and I've never had the problem again.
I have to correct this common misconception. Lacquer coating does not 'melt'. Hit up some spent casings with a blowtorch and you'll quickly see this. 'Poly' coated cases only came to the market because the US venue was so stuck in this line of thinking. Here's what really happens:
Steel cases don't have the elasticity of brass cases. This means when the round is discharged it doesn't fully form to the chamber; a small gap exists between the outside of the steel case and the chamber walls. In this gap, crap builds up. Now, along the same time period Wolf and other steel cases became more popular, the market with rife with South African battlepacks of 5.56. SA .223/5.56 is notorious for being made of relatively brittle brass. This means that when the SA brass expanded into the layer of gunk, there was often an insufficient amount of resistance on the extractor to pull out the round. Hence, the whole, 'no brass after steel'.
I myself run several rounds of brass cased ammo, to
pull out some of the gunk, for every several hundred rounds of steel-cased. The Box O' Truth did an article about this years ago here:
http://www.theboxotruth.com/docs/edu18.htmThe rule of thumb should really be, 'Don't run [South African] brass after steel'.
If one doesn't have a properly-speced 5.56 chamber, the risk is much higher of having a stuck case. It is notable that when Hornady released their training ammunition line (Hornady bullet and powder in a primed Russian steel case) they went with lacquer coated cases (which are far far better in regards to corrosion resistance than the 'poly' coated ones). In short: Poly cases exist because Americans are ignorant.