TexasRick,

"The old Lee Navy is basically a 7x57mm with a semi-rim. Same capacity and shape."

Not hardly. The Lee Navy DOESN'T have a semi-rim. The rim is the same diameter as the body of the case. You're thinking of the .220 Swift, which originated by giving the Lee Navy case a larger rim, plus necking down AND shortening the neck. It has about five grains less powder room than the 7x57.

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