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7mm-300WSM wildcat

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Old 03-15-2009, 11:18 PM
Silver Member
Join Date: Oct 2008
Location: Bryan, Tx
Posts: 284
7mm-300WSM wildcat

I am starting my first wildcat project. I am having a fully chambered 7mm-300wsm being built and I want to neck down 300 wsm cases to 7mm (this is not just prepping 300 wsm brass to eventually fit a 7mm wsm).

My usual new brass prep (not specifically in this order but...):
Norma brass preferred, winchester as a last resort
sinclair expander mandrel
flash hole debur
sorting by neck variance (keep cases with < 0.0015)
weight sort (remove top and bottom 5%)
neck turn to uniform neck thickness
primer pocket uniform
trim to uniform length
outside debur
polish w/ 0000 steel wool

I need input specifically regarding:

Should I neck turn the 300 WSM, followed by necking down to 7mm


Neck down the 300wsm and then neck turn the 7mm after case forming?

I will be using redding S type FL sizing dies w/ bushings.
What increments should be used to minimize work hardening?
Neck ream to minimize doughnut? When?

Since this cartridge is not uncommon, any help/experience is appreciated.
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Old 03-15-2009, 11:43 PM
Platinum Member
Join Date: Apr 2005
Location: Alaska
Posts: 3,227
Re: 7mm-300WSM wildcat

I don't have your cartridge but I've necked down quite a few cartridge cases over the years.

The first question is easy. Neck it down to 7mm before outside neck turning. There's no way to know that the case neck would size down uniformly if you outside neck turned the 300 first and then necked it down.

You should be able to neck down from 300 to 7mm in one step without causing any problem. I would anneal the case neck after sizing it down, personally, just in case the neck hardened some during the size down process. Whether you anneal before or after outside neck turning the 7mm neck, I don't believe it would make much difference.

I wouldn't inside neck ream at all. If at the time you ouside neck turn you cut back into the shoulder just a tad (that's what I do with my K&M Services outside neck tuning tool), you shouldn't ever form any dougnuts. The K&M Services cutter is angled at 35 or 40 degrees where the cutter contacts the shoulder to allow a slight thinning of the shoulder brass. Upon firing the case in the chamber that cut is blown to the outside of the case - leaving a slight recess on the inside of the case neck where the doughnut might otherwise eventually form.

Hope this makes sense and helps. That's the way I would do it. Someone else that has this specific wildcat may have keener insights on this specific cartridge case, but I believe this advice to be sound for your wildcat too.
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Old 03-16-2009, 08:03 AM
Gold Member
Join Date: Mar 2006
Posts: 829
Re: 7mm-300WSM wildcat

Here's some good info:
Vince B's 7mm WSM Record-Breaker (7 Win Short Mag)

7mm Cartridge Guide
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Old 03-16-2009, 10:02 AM
B23 B23 is offline
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Join Date: Oct 2008
Location: Spokane, Wa.
Posts: 928
Re: 7mm-300WSM wildcat

I'm sure i'm missing something quite obvious but I still have to ask. Why don't you just use 7mm WSM brass? I know the cases aren't identical but is there enough to be gained for the time involved?
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Old 03-16-2009, 12:14 PM
Platinum Member
Join Date: Feb 2008
Location: Sacramento, CA
Posts: 1,006
Re: 7mm-300WSM wildcat

I'll bet he likes norma brass better, plus the long neck of the 300wsm case may be an advantage. The slightly smaller volume may also be an advantage? 300 wsm brass probably has a better future than 7wsm brass anyhow.

Plus, the time involved is what most of us enjoy about reloading...

It seems like a good idea, to me. I may even go this route next time...
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Old 03-16-2009, 03:44 PM
Silver Member
Join Date: Oct 2008
Location: Bryan, Tx
Posts: 284
Re: 7mm-300WSM wildcat

Yep, norma brass is so superior to win brass. Not that win is bad, but it takes twice as much. I routinely order 100 brass to make 50 good cartridges. Might as well just order the Norma. I don't push my cartridges too hard so case volume is not a problem. Just over 3000 fps seems to be the best accuracy which has been easy to achieve. Easier on throats too maybe over the long haul. My thoughts for light turning before necking down are that maybe sizing down would be a little more even. I am not even against neck turning lightly before, and then again after, but maybe it is not necessary? I am surprised to see that I can neck down in one step!. I'll give it a go! Thanks in advance. Any more input is still appreciated.
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Old 03-16-2009, 04:44 PM
Platinum Member
Join Date: Apr 2005
Location: Alaska
Posts: 3,227
Re: 7mm-300WSM wildcat

You're stepping down the neck about 0.024" (.308-.284), so one-step resizing of the neck should be no problem whatsoever. Good luck and this sounds like an interesting cartridge - which is what drew my attention to your post in the first place.
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