making 300 Sherman brass

Hello all! I am currently looking at reaming out my 30.06 to 300 sherman. I have searched here and the rest of the internet in regards to making brass. I have been reloading about 15 years, but have never ventured into necking up/ necking down, false shoulders etc. Hoping I can get confirmation here that what i'm thinking is the process is actually correct.

First off, it seems 270 win or 280 rem is the preferred parent case, but can 30.06 be used? or 280 AI?

okay, assuming starting with 280 rem brass

1. anneal brass
2. use sinclair expander with .308 mandrel
3. use sinclair expander with 8mm mandrel
4. use 300 sherman FL die to neck down a little bit at a time until the case will chamber on the false shoulder with slight resistance.
5. load and fire fireforming loads

will any trimming or neck turning be required before or after after fire forming?

Thanks for the info....pretty excited by this cartridge!
Chris

Sounds good to me........cases shrink in neck length when fireformed correctly.
The amount depends, some of my Improved cases shrink from .015"-.030"+.

Cheers.

Steps 3 & 4 can be eliminated if you want to do it differently. You don't have to create a false shoulder. But everyone has their own method.

Trimming, maybe... Not sure on the neck-turning. I think most of Rich's reamers don't require it, but it would be best to ask him directly.

Necking up to 30 cal will produce slightly thinner necks, so you shouldn't need to turn necks. MagnumManiac is correct about OAL being shorter after forming, so you're good there also. I prefer to leave a false shoulder for FF, it produces more consistent forming, in my experience. I don't bump shoulders until the cases are tight to chamber. Sounds like you are on the right track.