"SteveB" writes:

Is a 7 x 57 and a 7mm Mauser shell the same thing? It's mostly metal

I don't know the reputation of
http://www.rifleshootermag.com/ammunition/seven_092105/
but they say they are the same:

"The cartridge is known by at least four names: Spanish Mauser,
7mm Mauser, 7x57 and in England as the .275 Rigby."