There is a peculariar shortage of 7mm mauser brass in my area. And being the resourceful though impatient guy that I am, I figure I can purchase some .257 Roberts or 6mm Remington and just neck it up. Can anyone divine a reason to use one headstamp over the other?

Thanks in advance.

If you use the 257 brass you won't have to expand the neck as far. .284-.243=.041, .284-.257=.027. Midway usually has 7x57 brass in stock, you ought to be able to get some from them pretty quick and save yourself the hassle.

Waldog;

In a pinch, I have necked up both 257 and 6mm Rem to 7 x 57. My preference is Winchester brass.

The 257 Brass is the + P type. Remington's has a heavier case to it, so the same amount of powder will mean higher pressures.

The 6mm Rem brass ( In Winchester) is the same story. The 6mm Remington cartridge is rated at 65,000 psi in SAAMI specs. If you are not overboard on the pressures in the 7 x 57 loads, either route work well.

I prefer the 257 route, just because I don't have to open the neck as much as I do on 6mm cases. 257 is almost 6.5 mm ( .264).

Good luck.

Why bother?

Go to Midway www.midwayusa.com

They've got 7X57 brass in stock by Norma, Remington, and Winchester.