300WSM to 270WSM

280fan

280fan

New member
I used to own a 300WSM. It's long gone and now I've acquired a 270WSM. I also have all the dies for both, plus 100 brand new 300 WSM Norma brass.

After studying the diagrams in my loading manuals it appears the 270 and 300 are both formed from the same case, along with the 7mm WSM.

My question is... can I neck down the 300 brass to accept a 270 bullet? I feel like I can but expect I really need a 7mm WSM die as an intermediate step.

Any thoughts on this? I've loaded .257 bullets into 270 Win cases, making 25-06 ammo, but that's a neck reduction of 0.020" Reducing the 300 WSM (.308) to 270 WSM (.277) is a reduction of 0.031". Is this doable in one step?

I'm not planning to do anything stupid, just exploring the possibility of using all this beautiful Norma brass.

Thanks.
 
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The 270 WSM & 7WSM are NOT the same case. The 270 and 300 WSM's are basically the same. The 7WSM has a slightly longer body (base to shoulder) than the 270 and 300.
Case Dimensions
Case Dimensions 2

But, you should be able to use 300 WSM brass to make 270 WSM brass, the 270 does have a little longer neck though.
 
Thanks for the reply. I agree, the 7mm WSM is quite a bit different from the other two, longer body length and considerably shorter neck. I wouldn't buy a 7mm die to use as an intermediate anyway, so it's a moot point.

I believe you're backwards on the neck length of the other two though. My Nosler manual shows a neck length of .295" for the 300 and .276" for the 270. If my cyphering is correct then the 300 case neck is aready .019" too long before I squeeze it in and lengthen it even more.

I wonder if this is even physically possible, considering the inside dimensions of the 270 WSM die? Maybe I should trim the 300 neck back to 270 length before I even run it through the die? You know it's going to grow back out during the downsizing.

I think I'll try it with one case, worst I can do is trash it, right?

Probably I should just drop the whole hairbrained idea, sell the 300 brass and go buy some 270. No fun in that though.
 
I believe you are right about the case necks. I'm away from my reloading books and was relying on diagrams from the internet. Anyway, I have heard of several people necking down the 300wsm brass to 270wsm and was at one time even thinking about it myself so I could have Norma brass for my 270wsm, but it shoots just fine with federal brass so I never bothered.
 
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