Hi, just haveing a thought. Could a RUM case be swagged down for use as a 375 Ruger? The RUM base is .545" and the Ruger is .530? The difference is about 1.5x the thickness of a paper plate. You might have to look at the primer pocket afterwards and maybe run a reamer in it if it got squished.
I see everybody complaining about no 375 Ruger brass. Why not make some?

I took a 375 RUM case and ran it up into a LEE 375 H&H seater die in a Lee Classic Cast press. It started pushing a ring of brass, so I took some sand cloth and tried to bevel the base a little. That worked fine and I was able to get the case almost all the way in, but stopped about 1/8" above the extractor groove. I used a mix of Bull Shop's case lube and RCBS case lube and went in about 3/8" in steps. The case ended up .533"
I think that a die with a gradual taper at the opening should be able to get most of it. I don't know if the web would be able to go through or not, but it might be possible to turn the base down slightly on a lathe.

It's easier and doesn't damage the base and
corner radius, if done like I do them. I take base down with my spinner lathe,at an angle from the base out, then swage. Use a lathe
with small lathe jaw to hold mouth of the case and small live center that goes in the primer
pocket, so the base of the case is out
where you can work on it. Then take base down
at the front of the extractor groove to size
you want. Use a multi-faceted floating cutting tool(file).But do it at an angle out away from
the base so case has a convex shape to the side
above base, It won't thin the sides enough
to hurt and then swage, and the swage wiil
go down over the heavy part of the base
easier.And you haven't jammed or crinkled the
corner radius.I took a 12ga FH case with .801
base and took it down to .780" to make
a 700NE case in a few minutes, and the swage
did the rest.Lathe and flat file and swage
dies can do about anything.Ed.

Thanks, that makes sence. Do you use a hydrallic press?

btw, you draw down, swage up at least in bullet making.

replied in bigbores...

you would need to turn some off the base to not reduce the case capacity, and not so much that you have weak cases.....

and would need 1" forming dies though, to not crack it

Lar45-Jeffe- I use big Ammomaster and big
Lee Classic for bmg,12ga FH and smaller
work. I have used Lyman Orange on everything
up to and my 585.Have the handles lengthened.
For 4bore/20mm use Ammomaster. It is reinforced
and leverage can be changed for 4bore,
by moving pin in bottom of ram. I did that so
compound leverage is the strongest
where I need it on middle of case with 4bore
1st die, then move pin for second die at base.
I have always felt that if hydraulics are
needed you may be crinkling the corner,
like with the 700DKT and one let
loose and blew up one the double bolts.Ed.