Watched an episode of NYPD Blue last night, in which steel casings from ammunition were an important detail in tracking down a spree killer.
Why/When would a round be made with a steel casing instead of a brass casing?
IME, steel cased ammo is cheaper. Nearly all cartridges I shoot are available optionally with steel casings.
Lots of people, including myself, are hesitant to use the steel casings, because of concern for increased gun wear.
The main advantage of steel is cost. Ammo with steel casing costs a lot less then brass, often as much as 50 percent less.
It has some disadvantages as well. Steel is harder and not as flexible so sometimes you’ll have spent casings that fail to eject. Steel casings often are coated in lacquer to prevent corrosion, and when fired, that lacquer melts and creates extra fouling inside your gun that can be difficult to clean. Some of the newer lacquers are better at this and don’t cause as many problems. And again, since steel is also harder than brass, it causes more wear and tear to your guns, though I’ve read that the extra wear and tear really isn’t that significant in most gun designs.
Once nice thing about steel casings is that all you need is a big magnet on the end of a stick to easily pick them all up when you are done shooting. That doesn’t work so well for brass. 
ETA: I personally only use brass. I don’t shoot enough ammo for the cost savings to really be that significant, and I’d rather not worry about the extra fouling or potential wear and tear issues.
What’s that you say? We used a roll around device called a Brass Magnet to police our range. I can’t find it listed anymore, but it is this device also sold as a nut harvester:
https://baganut.com/pages/how-it-works
Dennis
Steel can be and usually is harder than brass, but only if it made to be. It’s a common misconception that it’s always harder than brass simply because of the applications most people see them in. It does temper and fatigue much more than brass so I wouldn’t be comfortable shooting a reloaded steel cased round. I have, however, shot several thousands of new steel cartridges with no mishaps or jamming at all.
Debunking the Myth: Steel is NOT harder than Brass *(On your operating parts)
As others have noted, cost is the major factor - steel casing is much cheaper than brass.
The downside is it’s not practicably reloadable (ie, you can’t readily take the fired case, replace the primer, refill it with powder and add a new projectile and use it again).
That’s not an issue with things like 9mm Parabellum, where ammo is cheap, cheerful and getting flung out of the gun when it’s ejected anyway (so the firer may or may not be able to recover the case), but with larger or more expensive calibres, the inability to reload the case may outweigh the initial cost savings.
like has been said, cost. almost all of the 7.62x39mm, 5.56x45mm, and some 9mm Luger out of Eastern Europe is steel-cased. it’s cheaper than brass and aluminum, and they’re not concerned with reloading. plus, the SKS and AK rifles have their barrels lined with hard chrome so wear is less of a concern.
Certain guns were also made with steel-case rounds in mind as the primary round, I believe the FAMAS is the only major one.
a thing called “Brass Magnet” is not a magnet , it does not use ferro magnetism, its a roller that brushes the casing up into a collection bin.
But anyway back to the OP, the steel casing provides no functional benefit or drawback to the shooter on a spree. The only implication is that he didn’t care about damage to weapon and only bought the cheapest … to go on a spree. He planned to go on a spree when he bought the ammunition - he didnt just snap at the time he started the spree … he might have bought the ammunition months before, knowing he was going on a shooting spree, he wouldn’t have to worry about the damage to the weapon from the cheap ammo.
Wouldn’t the issue with steel case ammo be chamber wear, not barrel wear? Or are the chambers also chrome plated?
I wasn’t intending to imply that the shooter deliberately chose ammo with steel casing specifically for his shooting spree. I only mentioned it because that was the show where I saw it; the only importance to the plot was that steel-case ammo was such a rare thing that it proved useful for tracking the suspect’s movements (which would suggest that steel-case ammo is actually a crappy choice for a criminal).
It’s not common - most cartridges are loaded in brass - but it’s not rare or particularly unusual either.
Steel case ammo is not allowed at the indoor range I shoot at. I’m not sure why.
because often times steel-cased ammo from Eastern Europe also has steel/bi-metal-jacketed or steel-core bullets, which damage the range’s traps.
Thanks!
Way back in the day, I even saw some aluminum shell casings. Someone told me they were shunned because they couldn’t be reloaded, but I honestly don’t know.
My range sells Federal aluminum casing ammo.
I have shot thousands of rounds of both steel cased (TulAmmo) and aluminum cased (Federal) ammunition. I did so because of cost, shooting 3 or 4 hundred rounds a weekend. I haven’t had a single FTF, FTE, or anything else. Some say the steel is harder on extractors, but if I ever need to replace an extractor I’m positive that I’ll still be way ahead money wise. One major plus of the steel, as mentioned above, is the cases can be picked up with a magnet.
Recently my wife bought me a reloading press for my birthday, so my days of shooting steel are over. I’ve heard that steel can be reloaded, but the steel cased I’ve purchased are Berdan primed, so no go. Steel us cheap, but reloading is even less expensive and more fun!
CCI used Al for some of their cheap “practice” ammo. They were Berdan-primed so as to make them more or less non-reloadable.
Actually it doesn’t brush them up. it carefully picks each casing up between several fingers and a comb pulls them out and into the basket. Pretty clever.
Dennis