LRF,
The 7x57 case( including 7x57R) is based on the M93 case, which is .473" head diameter, instead of the M88 case( 8x57/8x57IR/IRS) which is .468"(both dims. max). Most European cases follow this, but American cases are usually made 06 size( incl. 6.5x55). You might keep this in mind if you intend to use European cases.
Mike
Further on the subject Mike noted. "Custom Cartridges" by Ken H, shows the head diameter of both the 7x57 Rimmed and Rimless at .474" diameter. Factory Remington 7x57 (rimless) actually measuring .466" diameter. As you know there are many many versions of the 8x57, and most show .470" to be the diameter, with one version being ~.468" diameter. However I don't think this info about the 8x57 is really not pertinent to the subject concerning the 7x57. Kind of apples and oranges, uness your forming brass and if the chamber is .473" I can't see any concerns at all.
(Opinion: I believe factories intentionally form their brass to the low specs because it better insures their ammo will fit in your rifle which is the mission of course)
