Neck 300wsm to 7wsm

[Kerry Guynes]

From what I understand I can neck down 300wsm to a 7wsm, but I will end up with a donut inside the neck! Perhaps I should just stay with 7wsm Winchester brass, but I have quite a bit of 300wsm brass. Has anyone necked down 300wsm to 7wsm?

 

[Steve Blair]

You will not have a 7mm WSM. That shoulder is a liitle farther forward. You will have a 7mm/.300 WSM, same as a 7mm/.270 WSM.

 

[WAMBO]

Yes you run the 300 brass into the 7mm die, since the 7mm has a shorter neck only part of the 300 neck gets sized to 7mm, just load as shoot, brass will fire form just like 6BR to 6 Dasher.

 

[B23]

Yes you run the 300 brass into the 7mm die, since the 7mm has a shorter neck only part of the 300 neck gets sized to 7mm, just load as shoot, brass will fire form just like 6BR to 6 Dasher.

Forming 7 WSM brass from 300 WSM brass, won't that leave you with a fair bit shorter neck once the brass is fireformed?

 

[WAMBO]

Yes compared to the 300 WSM case, the 7mm WSM has a shorter neck than the 300, the shoulder is farther forward but both cases have the same overall length, 2.100"

 

[B23]

Yes compared to the 300 WSM case, the 7mm WSM has a shorter neck than the 300, the shoulder is farther forward but both cases have the same overall length, 2.100"

That's my point, if both cases start at 2.100 OAL and you push the shoulder forward .038 when it's fire formed I can't see how you aren't going to be left with a shorter OAL case on the one you fire formed. That extra .038 length in the body of the case has to come from somewhere.

I've never formed 7WSM from 300WSM but I've formed plenty of AI'd or Improved cases and after fire forming they are always shorter than that same case was before it was fire formed. Will it be a problem in this 7WSM scenario, probably not, but I believe the overall length of those cases will come out shorter than they are before they're fire formed.

 

[WAMBO]

You are correct, I didn't think about that.
When I fire formed my 338 AI the OAL of the case was about .010-15" shorter but never gave it much thought as I never had to trim them to length again.

 

[Steve Blair]

I have formed a lot of .300 WSM from .270 WSM because the latter was 2/3 the price at the time. It fireforms ~.015" shorter but doesn't seem to cause any problems. I set my Giraud at 2.075" and it works fine.

 

[dannyjbiggs]

I have formed a lot of .300 WSM from .270 WSM because the latter was 2/3 the price at the time. It fireforms ~.015" shorter but doesn't seem to cause any problems. I set my Giraud at 2.075" and it works fine.

That's quite a stretch, Steve! Most I've ever necked mine up to is 7mm. Now, when I see someone soliciting .300 WSM, I can offer .270 WSM in confidence.

 

[Steve Blair]

That's quite a stretch, Steve! Most I've ever necked mine up to is 7mm. Now, when I see someone soliciting .300 WSM, I can offer .270 WSM in confidence.

Danny - It must be done in two steps. I go from .270 to 7mm and then to .30. When I tried a direct expansion, it split necks.

 

[Kerry Guynes]

You don’t think I’ll form a donut inside the case from necking down the brass