Bwana;It may take some time time to get to shooting this rifle.
I plan to build it on a montana action,so I think you be shooting before me.
Ross Seyfried wrote a artical on the Imp's in Guns&Ammo July 94.
The only load in it was Fac. recom. for 250gr /Imr4831/93 gr Max for 3079 ft/sec.
I think a good place to start would be the 358 Norma and the 358 STA.
The A square reloading man. has a good selection on both.

Regards Martin

Hi Martin. Good choice with the 360. I knew a guy from Edson that hunted with one back in the early 90's, everything I saw hit with it (elk and bears) went down like it was poleaxed. The hammer of god from a rifle! Only thing I didn't care for was he built it light to carry, and recoil was phenomenal (no brake or magnaporting). How's the 500 A square coming, by the way? - Dan

For what its worth, I have been shooting a 338 Imperial for several years and when the 300 Ultra came out it improved the availability of brass for the rifle. When I run the 300 Ultra through my dies it only changes the angle of the shoulder slightly. My rifle is about 10lbs and the recoil is not bad at all.

Steve

Bwana; You are right the Rum is .004" bigger.

Here is what happened,I have one loaded 360 Imp in my cartridge collection and a RCBS 360 die set.
Like you stated the Rum is .004" bigger if compared to the Imp case.
If I preload the die in the press the resized case comes out the die at .002" bigger and the datum line is .005" longer than it's should be.
If I stick a .005" feeler gauge between the case and the shellholder it comes out at .001" bigger and the datum line in the right place.
The reamer is with a gun smith in B.C.
So I don't know the dimentions of it but the way I think is he can cut the barrel to the original dimentions and I can controle the shoulder setback with the die to 0 headspace
If the case diam. would be a problem I can always make a sharper shouldered die to push it to where I want.
Of course if need to I can grind .005" of the shellholder.
I know this seems like a lot of fiddeling around but it's only a one time thing and I am hellbend to make this work I want a beltless 358,have several 338's and 375's so what can I do?

Regards Martin

Martin, be careful about interchanging the RUM and Jeffery brass.
The RUM is a nominal .005" fatter at the base.
Laugh if you like, but if you cut your reamer for a Jeffery case, and run high-pressure loads in it with RUM brass, it may get sticky on you.
Unless you have a loosish chamber.
I think SAAMI tolerance is .008" (correct me if wrong) and depending on who made your reamer, the real base dim of Norma Jeffery (for instance) is closer to .541", so at .008" maximum tolerance, you have room for .0015" on all sides of the RUM brass.
Maybe no problem, throw in some grime and high pressure, maybe a problem.
If it's chambered for the nominal .544" 404 spec, you have much less problem, maybe none to begin with, and likely none with low pressure loads at any rate.
Crazier conversions have been succesfully practiced.
Just some FYI.
BTW, I'm on the edge of my seat awaiting the arrival of my 358-404 wildcat, basically the same as the Imperial, but the tolerance is cut in half, and measured off of Norma brass, throated for the 280g Swift A-frame; love to swap load data with you if/when.

can somebody tell me if this the same as the 338-404 and if the 338 ultra just made them standard? cant find much on the dimensions of anything searching around the net.

Check out what was once caled the 338 Imperial Magnum. It was put together by a BC firm back in the late seventies/early eighties, and is just what you described, a 338 on a full length, blown out, 404 case. Basically, a 338-300 Ultra Improved. They had a whole line of calibers based on this case, and there is still a 'smith in southern BC that chambers for them (as well as a few other 'smiths, I'm sure). - Dan

To be exact, it is the 300 Ultra necked up to 338 with no changes.
It's not exactly like the 338 Ultra, because the shoulder is in a different place. (More forward I think, greater capacity with smaller bullets.)
The 338 Ultra is a wee bit shorter, to fit the cannelure at the proper COL for standard bullets.
When you say 338-404, you have to say which one, b/c anyone can take the 404 basic case and put the shoulder, taper, case length, wherever they like (within reason) and call it 338-404.
They will all perform somewhat similarly, but the improved versions (like the Imperial Mag) will have a slight edge.
There's also the Yogi and I think Tomahawk (but maybe that's 308?), which are on the improved Ultra case.