Help needed: How do I neck size down to 7mm from .30 cal?

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prairieguy

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Hello,

I've got a pile of 300 WSM brass that I want to neck down to 7mm. I've never done anything like this before and need help.

I've got a neck sizing die for the .300 WSM. Can I just swap out the bushing for one suitable for 7mm and get going of are there other steps I'm going to have to do either before or after?

Will I have to do the resize in more than one stage with a couple of neck bushings?

I know I'll have to trim to length after I do the resizing. Anything else?

Should I run the cases over through a 7mm neck expander die after the resize or will that make any difference?

Any hints or suggestions are greatly appreciated.
 
Problem is I'm not making 7mm WSM. I'm going to make 7mm - 300 WSM, a wildcat that's similar but not identical to 7mm WSM. It has a longer case neck length.
 
Measure the outside neck diameter of a fired 7mm case and then the diameter of the new case with a bullet seated in it. Just make sure you have at least 2 or 3 thou of neck expansion room.

I would expect the new neck wall to be slightly thicker. I have necked 308 down to 243 in a single pass, so would not expect your change to be a problem.
 
you'll have to neck them down with a secondary shoulder to headspace in your 7mmWSM chamber and fireform to blow the shoulder ahead...not a big deal.........the headspace is about .04 longer IIRC..I necked some 270WSM up to 300WSM last nite...same length on these two...the 7WSM is the oddball of the three.....and maybe the best of the three...can't see why the 270WSM is more popular than the 7WSM......
 
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The 7WSM is longer from the base to the shoulder than the other versions. This is to prevent the 7mm version from being chambered in a 270WSM. With your 7mm-300WSM be careful if you own, or hunt with, someone who owns a 270WSM. Make damn sure the cartridges don't get mixed up.

I would neck down a bit at a time until you get a case that just chambers in your rifle. This will leave the case headspacing on the secondary shoulder Rembo noted. Fireform these cases with starting loads using whatever odd bullets you have on hand.
 
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