I just recently necked down a bunch of 30/06 to 25/06. This is the first time I've necked anything down so it got me wondering.

Is the neck thickness going to be a little thick? Will this brass last as long as original 25/06?

Probably dumb questions but thanks in advance.

The necks are definitely thicker than when you started. Whether or not they are too thick depends on your chamber, your sizing die and the actual (not nominal) diameter of the bullet seated in each one.

Seat bullets in about 5 randomly chosen unprimed, empty cases. Measure each neck at @ 4-5 different diameter points. Compare to your chamber cast. Your case neck's LARGEST diameter must be smaller than your chamber's SMALLEST. You want @ .003-.004 clearance for most hunting rifles.

What, you don't have a chamber cast? Get one! In the meantime, compare to SAAMI cartridge, (not chamber) specs.

If they are too thick, thin them by outside turning. It is much easier to obtain uniform neck thickness by turning the outside rather than reaming the inside.

Considering the cost of the .30/06 brass, plus the time and trouble, you would have been much better off to just buy new .25/06 brass.

[ 05-13-2003, 11:53: Message edited by: wingnut ]

1) Incrasing powder charge makes some pressure increase.
2) Heavier bullets make some pressure increase.
3) Bullets too big for the bore don't make any pressure increase.
4) Faster powders make some pressure increase.
5) Jamming the bullet into the lands makes a pressure increase.
7) Magnum primers make a pressure incrase.

The above changes that make changes is pressure are small compared to the change in pressure with a change in how much the chamber neck pinches the bullet.

I necked down 308 brass to .243.
All three shots have the same bullets, powder, primer, and brass. The differences on pressure are due to very small changes in neck thickness.