I never owned a center fire semi-auto handgun or rifle until recently. Now that I do have a mini 14 and a 9mm handgun, I can see why you would contemplate steel cases. I do not reload for my 9mm, I buy cheap ammo to practice with and buy more expensive self defense ammo for carry. I have saved the brass, even though I have no dies for it to reload with. I did have 400 rounds of new 223 Winchester brass setting around and loaded it up for the Mini 14. My first session, I was digging through the grass for the empties. I lost several, too many in my cheap a** mind. On my second session, I laid out a large plastic tarp to catch the empties. This time I got most of them. I can see where you would want to get cheap brass (steel) and fire it once and forget it. So steel cases, if you pick them up from the range for free to reload with would make some sense to me. Reload them once and forget them, do not worry about picking anything up. Or if you are buying your ammo and accuracy is not an issue, cheap ammo is best and do not worry about picking up empties.
As for my revolvers, bolt guns, single shot guns and pump guns I will stick to brass cases, thank you. If I am going to worry about the cost of the brass, I can always download the brass a little and make it last a long time. Long enough to out last steel by quit a bit. If you can get steel for free, then I would guess it is cheaper. But if you buy the ammo and fire it and recover the cases, I am not so sure it is that much cheaper. It may be more expensive. the cost difference between brass ammo and steel ammo looked at over the reloading life of each is.... You can get several reloads out of brass, especially if you periodically anneal the case mouths. Even if you buy the cases new and reload them enough times, the cost per shot goes way down. You can easily get 10 reloadings out of straight walled cases and you can get 5 out of bottle necked cases. You can get much more than that if you do not load right up to the limit and anneal the case mouths every so often. If a case costs $.50 and you get 10 reloads out of them, it costs you a nickle per shot. If your brass for a handgun costs $25/100 and you can get 10 reloads out of them, your cost just went down to two and half cents a shot, about the cost of your primer. Less if you reload cases more than 10 times. Bullets are now your most expensive component. If you cast your own bullets to save money or what ever, then the life of your brass just went up too. Now you can get 20-25 maybe more reloads out of a case because you are loading to low pressures. So if you can recover your brass, the cost is not that much per shot.
There are things you have to watch with steel cases, rust is one of them. So you would have to be careful about long term storage. Would you trust a steel case where there was a rust pit? If you oil the cases to prevent rust, will it not grab the chamber walls and cause excess pressure on the breech face? If you coat it with a varnish, will it stick to the chamber walls and be difficult to extract or not extract at all?
To me the disadvantages of steel cases vs brass is just too great to even mess with. The cost difference is just not that great to chance any potential problems. However, if I could get boxer primed steel for real cheap (free) in 223 and I would reload and shoot it soon after, it would make some sense to me. I really do not like to hunt for empties and it effects how much I shoot the Mini 14 because of it.
I do not shoot my semi-autos that much. This is because I get a bigger kick out of placing one shot exactly where I want it, than putting 10 rounds down range in 10 seconds. I know that there are ARs that are very accurate and can place bullets almost as well as the best bolt guns, but you have to start chasing your brass around. I do not think that anyone that is very serious about accuracy would shoot steel cases anyway. But each their own, if you like to rip up the range with rapid fire, then that is your right and have at it. My departed Brother-In-Law is the latter type. He loved to put as many bullets down range as fast as he could. He never reloaded a single round, he bought every thing he shot. He never understood why I would convert a bolt gun with a magazine over to a single shot. To each their own.
As always, this is still a free country and you are welcome to do what ever you wish. If you wish to reload steel cases until they fail, that is your business. For me I will stick to the brass cases, the real cost is not that high, just a few pennies per shot. I have enough brass 223 (in ammo cans) laid away to get me through for quite a while. If I am stormed, I could not shoot every thing I have without melting down the barrel, but more than likely, I would go down long before that. If the cost of brass cases does get that high or I can not afford them any longer, I will load up what I have left and save them for the defense of the home front and a few for hunting. I will shoot rim fires for my pleasure. I have more than enough to last me, even if I do not buy any more.
Good Luck and Good Shooting