Well, as the 7mm x 57mm is a true 3" cartridge it's not going to fit in a SA. There are some 'intermediate' actions, but there're customs, not production like a Rem. 700/Win.70/Ruger 77. I've built several 6mm Rem. AIs over the last couple of years using LAs. The 6mm Rem case is based on the 57mm Mauser cases. They feed just fine without alterations. In a SA you'd need a mag box with an inside length of approx. 3 1/16", and I don't think that's a possibility even with an 'extended' box. See why I said "someone who doesn't know what they're talking about". Kinda' self explanatory if you look at the loading manuals for loaded cartridge OALs. The large ring military Mausers have an inside mag length of 3.315" for the std. length and 3.232" for the intermediate lenght and those cartrides and actions were designed around each other. There is an exception or two in the std. length Mausers, but they were built with cartridges other than the 57mm in mind.
