Conventional wisdom tells shooters that steel-cased ammunition is harder on a gun than brass. That is not the case. Bi-Metal and steel-jacketed bullets will wear a barrel faster, but steel-cases typically will not wear a bolt and chamber faster.

Now, Steel can be harder than brass (and it typically is). The steels used in bolts, barrels, etc are typically much harder than either steel or brass ammunition. The steels in steel-cased ammo is usually very soft.

YouTuber SaltyShellBack has the luxury of access to a Rockwell hardness testing meter and tested some off-the-shelf brass and steel ammunition.

Personally, my 3-gun teammates only shoot steel-cased and have plenty of rounds down the pipe with no issues.