new brass

[Old Jim]

My question for today:

New brass, as in unfired, when ran thru the sizing-die I use for fired cases, is untouched by the die, save the first 0.30" of the case. Yet when fired using the same load as in the fire-formed cases, the groups are lousy ... 4-5" groups @ 200, as against 2" groups from the fire-formed ammo.

Any suggestions as to why this is?

I probably knew at one time, but you know how old brain-cells get !