Making 7 WSM From 300 WSM????

I size down 308 brass to make 7mm-08 brass and its not hard to do. I dont worry about neck diameter either.
I dont know if it would be any different doing that to your brass as long as the dimensions to the neck are the same.
 
The shoulders on both the 300 wsm and 270 wsm are shorter than the 7mm so if you neck it down it will be shorter. I don't know if you can get away from fire forming them first.
 
From what I've read and been told by my gunsmith you can neck down the 300 WSM brass by running them through your 7 WSM sizing die and fireform them just like fireforming Ackley brass.

I'm in the same boat as you I'm just not sure I want to waste barrel life fireforming brass, we might not have much of choice here before long
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I believe the 7mm WSM is the best of the WSM bunch. That said I have heard you can not make 7mm WSM from the 300 WSM or the 270 WSM. If that is true I do not understand why they would have designed it like that. I love my 7mm WSM.
 
http://forum.accurateshooter.com/index.php?topic=3790857.0

This is from the link above. A little work, but would work, I guess.

Quote:If you already have your 7mm WSM dies set up the way you want them, you can just use your 7mm WSM die to neck down the 300 WSM case. Be aware that the shoulder on the 300 WSM case is 40 thousands shorter than the 7mm WSM case. The 7MM die will create a "false shoulder" on the resized 300 case. If it were me, I'd neck down without using the expander ball in the sizing die, then expand with an Expander mandrel (K&M or Sinclair).

That shoulder will be the new location of the shoulder/neck junction on the fireformed case once it's fired in the chamber. The false shoulder is supposed to keep the case from stretching at the web, but for good measure, I'd load the fireforming loads with the bullet into the lands and use a mid-range load of your normal powder for fireforming. That will keep the base of the case firmly against the bolt face when you fireform.

I have a few 300 WSM Norma cases sized that way, but haven't shot them yet - still hoping the 7mmWSM Winchester cases will work OK, but I'm having my doubts.....too much neck thickness variability for my tastes.
Elkbane
 
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