This may be way off thats why iam asking before trying it.

[Brians356]

That's why it's called "reloading". Starting with unfired cases is cheating.
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[Rsadams]

Lol....

 

[fguffey]

OP if you don't want to neck turn, starting from 257 Roberts will leave the necks not much thicker than 6mm brass, and you should have ample clearance without turning. But you will finish up with something of a donut which means you won't want to seat bullets deep enough to run into it.

When going from 257 Roberts to 6mm Remington the neck gets longer by .029”± a few. If a donut appears where did it come from or what caused the donut? When necking down the neck gets longer, when necking up the neck gets shorter. Again; I form cases that shorten .045” from the end of the neck to the case head.


F. Guffey