338-378 Wthby from 300-378 brass

[normo]

Has anyone had any luck necking up 300-378 to 338-378?

My buddy just picked up a box of Nosler 300-378 at the Shooters Pro Shop and was told he could neck it up with no problem. After crushing two shoulders, we have put this on hold until we get more info.

Dies are RCBS 338-378, applied case lube to the outside and the inside of case neck, worked it slowly, it began to expand the neck and then ended up crushing the neck down into the shoulder.

My first thought is needing an expander between 30 cal and 338 to ease the process, otherwise I'm at a loss.

 

[DrMike]

It can be done, but expanding the neck with something like a Sinclair expander mandrel first could be helpful. I would ensure that I was using a tapered expander ball in the sizing die and I would definitely use Imperial Sizing Wax rather than Case Lube. The Wax has more lubricity to avoid galling the case.

 

[IdahoCTD]

Weatherby calibers are harder because of the double radius shoulder. A long tapered expander like the ones in Lee dies work the best. Hornady dies aren't bad either. RCBS dies probably have the worse expanders. I use Imperial Sizing Wax also.

 

[boomer68]

You could also purchase a tapered expander from Redding. This is what I plan on using.

 

[normo]

I like the wax idea for sure and yes the RCBS expanders are rough, not too mention the knurled section in the middle of the tapper prior to the final expander size.

Thanks for the suggestions and tips.

Not sure just yet how this project will play out.

 

[FOTIS]

No problem with the Hornady elliptical expander