If the bullets are not attracted to a magnet, they are probably jacketed with copper nickel, which is the metal the silvery parts of quarters and dimes are made of. That kind of silvery bullet jacket was more common in Europe than in this country, but it was used here too. I think steel is pretty unlikely for a US pistol bullet, and even less likely to be un-corroded after 100+ years.
The brown jacketing material is often called gilding metal, I can never remember why.
I agree with the others above that these were made for the US military in the First World War. I have some just like that that came in half-moon clips. The primers are lacquered, which sometimes flakes off.
PS - Now that I think of it, copper nickel which is high in nickel is also attracted to a magnet, so that test is not definitive. That used to be why Canadian dimes and quarters would not work in US vending machines. The Canadians now make those coins of stainless steel, and they still don't work.