Forming 6mm REM from 7x57

[CacheCropp]

I’m running short on 6mm REM brass and also would like to find better quality than the Remington brass I’ve been using. Before I buy Lapua 7x57 brass, how hard is it to neck down?
Was thinking I could use different bushings in 6mm REM dies. If I’m starting with necks that are about 0.312 OD (7x57) and aiming for necks that are about 0.271 OD (6mm REM), could buy bushing for my 6mm REM die at 0.298, 0.284 and then a couple for the final product 0.269, 0.270. Maybe have to turn necks in the end?
There’s also hydro forming dies but I’ve never used them, don’t know the expense or how well they work.

 

[std7mag]

I'm making 257 Roberts, and 257 Roberts AI casings from 7X57 Mauser.
Simple one pass, neck down in a 257 Roberts full length sizing die.
Fair bit of trimming though.

I'm using PPU brass. I don't really have the disposable income for Lapua. And I've gotten 30 reloads with no issues with the PPU running at +P loadings (58,000psi).

With another .014" necking down, I'm not sure if you will get the dreaded donut or not. You may have to internal neck ream.

 

[358WCF]

Good luck finding Lapua 7x57. I was using PPU 6.5x57 brass for a 257 Ackley until Raven Rocks got some Norma 257 Roberts. They may still have some.

 

[CJ6]

I’m running short on 6mm REM brass and also would like to find better quality than the Remington brass I’ve been using. Before I buy Lapua 7x57 brass, how hard is it to neck down?
Was thinking I could use different bushings in 6mm REM dies. If I’m starting with necks that are about 0.312 OD (7x57) and aiming for necks that are about 0.271 OD (6mm REM), could buy bushing for my 6mm REM die at 0.298, 0.284 and then a couple for the final product 0.269, 0.270. Maybe have to turn necks in the end?
There’s also hydro forming dies but I’ve never used them, don’t know the expense or how well they work.

You can do it in one pass without issues.
Anneal after and turn necks as needed.

 

[std7mag]

You can do it in one pass without issues.
Anneal after and turn necks as needed.

Would OD neck turning get rid of a donut?

I've never had to anneal after necking down.
Even after then fire forming to AI, I only anneal after 2-3 reloads.

 

[CJ6]

Something I've done since I started necking down cases. I've had 284 Win cases necked to 6mm split after just a few firings (like 4-5) so I started annealing after initial necking down. No issues after that.
As for your OD that will depend on chamber neck and your actual brass thickness as those two vary.

 

[NZ_Fclass]

Things change. I used to have to buy Federal 6mm brass to make 7x57 and .257.