Do NOT use .30-40 brass to make .6mm Lee Navy.

[andiarisaka]

I wouldn't go so far as to say without a doubt. I've seen the pics, it wasn't just brass failure, he had some very high pressure that made the brass fail. There is the possibility of overheating the brass when turning off the rim and cutting the extractor groove. However, I feel that what he had was a rough throat and a thick jacketed bullet, with the bullet temporarily acting as bore obstruction, raising pressure to the "we don't wanna go there" level. The head of the 30-40 doesn't need to be pared or swaged down to make 6mm Lee from it. Todays 30-40 brass runs around .453 at the head and will actually seal the chamber better than the original 6mm cases. So, just because he "thinks" the case was at fault doesn't necessarily make it so. Comparing some recently made Remington 30-06 to 30-40, there is some difference in the thickness of the web, .020". Anyone cutting an extractor groove in 30-40 cases should bear that in mind and decrease the bevel on the forepart of the extractor groove. I believe the Lee rifle has an extractor with a very square face, but I'm not lucky enough to have one to look at first hand to verify that. Does someone have an original 6mm case that they could measure the thickness of the web? I get .173 for Krag, .193 for 30-06. I don't mean the thickness left in the primer pocket, but the thickness of the whole head.