Last weekend I had the opportunity to visit the Manatee Gun Club range in Myakka, FL.  Notably they are the only open-to-the-public 1000 yard range in the Sunshine State.  I limited my shooting to 565 yards where steel targets and truck tires live on the berm.  Long story short, I brought my homebuilt AR-15A2 (FN 1x7 surplus barrel) and approximately 500 rounds of various steel cased ammunition. 

Steel is not as malleable as brass and thus does not expand to seal a firearm's chamber as well as brass.  As a consequence, there will be significantly more case blowback than a similar brass cased cartridge.  This is evident in the pictures below as you can see the amount of carbon residue stuck to the side of the steel casing I had to manually eject via cleaning rod. You can also see the nice section of missing case rim material in the approximate shape of an AR15 extractor. This can be a more common problem with uneven case coatings such as "lacquer" found on Brown Bear (not really lacquer) or "polymer" found on Wolf and Tula (who knows what this really is).

The moral of the story is the bring a good cleaning rod when shooting copious amounts of steel cased ammo.