[Scharfschuetzer]

Take a look at the flash hole(s) in your steel cases. They may be Berdan primed and if so, they will have two flash holes and an integrial anvil in the primer pocket. Given that, the case will not take standard American Boxer primers and will require Berdan primers as well as a special depriming tool and possibly a different diameter seating stem for your primer tool.

I'm sure it's been done, but I don't know anyone who has loaded steel rifle cases.

In the early 70s, I did load some WWII US 45 ACP cases that were mild steel as an experiment. They were Boxer primed with the standard LP primer size and I enjoyed some success with the project. Accuracy was fine, but in the end it was just an experiment and I haven't tried it again.