When I first bought my AR-15, I initially decided I would only shoot brass-cased ammo. Steel-cased ammo, I had heard, was dirtier, it’ll wear out your barrel faster, sometimes the lacquer would cause cases to get stuck in the rifle, etc etc. So at first, I stuck with brass ammo. Naturally, this was right after Sandy Hook, and when I could find it, I was paying $0.50 – $0.75/round for brass cased ammo.
Fortunately for me, along came the Lucky Gunner Torture Test. It’s a really long article, so here’s the TL;DR version: they shot 10,000 rounds of 4 different types of ammo (each through it’s own rifle). In the end they found that apparently steel cased ammo will in fact wear your barrel out faster (at least the way they ran them). BUT, with the amount of money you save shooting steel vs brass, you’ll have enough money to buy a new barrel (replacing your barrel at 4,000 rounds), and still have spent less money than purchasing brass cased ammo. See the chart below:
Note that this test references AR-15 ammo; YMMV with pistol ammo. Personally, the price difference is negligible enough that I’ve stuck to shooting brass cased ammo in my 9mm Ruger SR9c. But steel-cased it is for my AR-15.