I have quite a few 378 cases, and no 460 and was wondering if this is feasible without annealing? Would I need a tapered expander die?

You could try one, go slowly and use plenty of graphite inside the neck, if it crumples, this will tell you you need an intermediate step, I would think a 416 expander would work well.
I tried to neck up 375H+H brass to 458 Lott in one pass, it didn't work at all, I had to go up in 3 steps and made my own tapered expanders on my lathe, .400", .435" and then the 458 Lott die. This was the only way I could get it to work without the shoulder crumpling, you may not have trouble because the shoulder is larger and stronger than the H+H brass.
Good luck.

Cheers.

I think it will work well.
.375 to .458 is not a bad stretch.
RCBS makes a .375-.458 tapered neck expander as well as a .30-.375.
I have used both of those sequentially to neck up .338 Lapua Magnum first to .375 and then from .375 to .458, two quick and easy steps,
and a bigger stretch than you will need to do.

I have also necked up many, many 460 Weatherby to .510 for the 500 A-Square in one step.

The .338 LM cases I used were nicely annealed, as new from factory.

Ross Seyfried Rule of case forming: Anneal before necking up and after necking down.

Another easy way, after you get the 460 Wby:
Simply fire any full pressure 378 Wby load in a 460 rifle.
The bullet will rattle down the barrel and perfectly form the case to 460 Wby. Harmless.
I routinely blow out .338 Lapua Magnum to .500/.338LM this way.
I might lose 1 out of 200 cases to a minor neck split, with Lapua-made brass.

Norma-made 378 Wby brass should be good too.
Anneal before necking up to .458, especially if it has been fired previously in the 378 Wby.

.458/.338LM made by necking up .338LM with RCBS tapered neck expanders:

Thanks RIP. I will try the shooting of 378 in the 460. I have some cheapo Hornady bullets that I can use.

i just shot the 378wby ammo out of my 460wby, easy as...............

Don't follow my bad example when expanding .264 Winchester case necks to .410" for a new wildcat I was experimenting with. I had the bright idea of loading a forming load into the case and topping it with a graphite wad. Then I dropped a .40 caliber round ball into the chamber and loaded the case behind it.

The first few cases formed perfectly, but then unbeknownst to me I used an undersized ball, which lodged about six inches in front of the chamber. The result was a nice goose egg, resembling the one on a pre-64 Model 70 Winchester barrel. Fortunately, accuracy was not affected, but that was pure luck.

The cartridge is a good one for avoiding the fictional .400 Whelen shoulder problem, and it fits very neatly into the 1937 Mauserwerke Portuguese Mauser I used to build it on.

IanD,

Can't you find some one to trade with by adver-
tising here, and on other appropriate sites?

I just use a fast powder and corn meal.

Prime a case drop in 18 - 20 gr of Red Dot, ect. Fill with corn meal, use a pencil to compress a bit, a small bit of TP in the neck, and fire.

I have taken 300 Wby - 458 Lott. Anneal the case first, for fewer case loss.

Keith

quote:

Originally posted by Hog Killer:
I just use a fast powder and corn meal.

Prime a case drop in 18 - 20 gr of Red Dot, ect. Fill with corn meal, use a pencil to compress a bit, a small bit of TP in the neck, and fire.

I have taken 300 Wby - 458 Lott. Anneal the case first, for fewer case loss.

Keith

Thanks for the info. Sorry to sound stupid, but what is TP?

Toilet Paper

I 2nd the cornmeal and TP. I have used that method for blowing out 338 to 458 win and 375 H&H to 458 Lott

Jason

I use Unique, Cream of Wheat and a plug made from a bar of soap to make a plug to blow .300 Win Mag out to .458. They need to be trimmed, whereas .338 wouldn't.

A quick and dirty method of necking up is to take some junk spire pointed bullets in the desired caliber and seat them upside down. Then you can either fire them or pull them.

When I neck up .300 RUM cases to .338 Edge I load them normally and just ram the big 300 grain SMKs into the necks. The run-out on those rounds is horrendous but no worse than the ones I do over a tapered expander or Sinclair mandrel. They are straight after being fired the first time and strangely the accuracy is barely affected. It doesn't seem to show up until well over 600 yards.

quote:

Originally posted by Dogleg:

A quick and dirty method of necking up is to take some junk spire pointed bullets in the desired caliber and seat them upside down. Then you can either fire them or pull them.

Yep, that works very well.
That is how I did it when I lacked a tapered neck expander for greater than .458 caliber.
From my post above:
"I have also necked up many, many 460 Weatherby to .510 for the 500 A-Square in one step."
I used 35-cent milsurp 50 BMG bullets (priced last century) and pulled them
from the neck-expanded 460 Wby brass with vise grips and reloading press: Voila! 500 A2 brass.
One AP-blacktip 50BMG bullet can be used forever with care.
But of course I fired some of them backwards too.
Neck-up and fire-form is a single-use per 35-cent ball.

A suitably long-nosed .458 bullet would do nicely in necking up 378 Wby to 460 Wby.

That's a great idea with the bullet seated upside down. Any suggestions for what bullet to use?

An old Barnes XFB smooth-sided .458/500gr, long and pointy.
Or any of the shorter ones or even a TSX.
Of course a specialized VLD long-nosed bullet with a greater ogive radius might be slicker.
Something for the .458 Steyr or whatever you call it?

Just looking at my .45s, an A-Frame or TSX would work as well as anything.

Great info guys. Will give that a try.