264 WM Case from a 300 WM Case question


Well-Known Member
Mar 13, 2007
Ok, rather new at 'down-sizing' a case.

It's a pretty good stretch from the 300 WM case down to the 264 case. If I run it through a 7mm Mag sizer, do I nee to full-lenth size it or can I just get a neck-sizing die as a mid-step?

Or, short of buying 264 brass (with all of the 300 WM brass lying around here) can I just run it straight into the 264 sizer and trim?

Or, any other ideas?


Well-Known Member
Feb 25, 2008
I would run it through in 2 steps, first I would neck down to 7mm, then I would run part way into the 264 die with the expander removed, only just start to push the shoulder back, size down in stages in this step if you can, rotating the case a 1/4 turn between sizing helps, then check the neck length and trim before final size and neck expansion with the sizing button. Final step would be to measure neck thickness, I believe it will be thicker than regular 264 Win Mag brass.
If you do this, tell me the OD of your finished necks and I'll compare to my 264 brass I have here.

BTW, I did this, 300WM to 270 Weatherby with mixed results. No matter how slow or how much or little lube I used, the shoulder area would get wrinkles in it. EVERY CASE had them, some far worse than others.
It was far easier to use 7mm Rem Mag brass and fireform to suit, in your case, all you need is to run it through your 264WM die, seat bullets and shoot.

Let me know how you get on.



Well-Known Member
Apr 22, 2008
Dillon Mt
I have not had good results pushing the shoulder back while sizing the neck,

I would use a .338Win die to first set the shoulder and then follow with sizing the neck.

You will probably need to deal with neck/shoulder junction as it will likely leave a donut in the neck.

The cases may need to be annealed first.

Hmmm........ trade/sell the 300 brass, get some 7mm brass and make it easy.