338 Imperial Model 70 Winchester Problem

In an impulse buy a few years back I picked up this orphan before doing my online research. At the time I had more idle time than brains and bought a $900 problem from someone else. Not wanting to dump this rifle off on some poor unsuspecting sole I have decided to salvage what I can and move on. As-Is it has a 27" heavier than factory profile custom barrel in 338 Imperial Magnum. I have the dies and some 404 Jeffery brass. I determined that the extractor was shot when I could not extract light loads from it at the range. At this point I have some parts lying around ( super grade stock and bottom metal) and would like to put something together I can use for Elk hunting. YES I know I can just go out and buy a nice 338 WM or 340 MKV Weatherby but would prefer to use what I have for now if I like it. Here are my questions for you Model 70 experts.

1.) would it be possible to use the current barrel and some how shorten it so I would be in 338 RUM? I don't have chamber drawing on the Imperial so I am at a loss.

2.) since the action was a 300 Weatherby Model 70 post 64 Classic CRF could I just pick up a factory Winchester take off barrel in 338 WM and have it rechambered to 340 Weatherby?

Ultimately I would like to have a good 338 RUM or 340 Weatherby for less than a new rifle if possible.

Thanks Brad

Brad,
I wish I could tell you on the setback and rechamber - iirc the imperial has less taper, and therefore a larger diameter shoulder than the rum -- though, actually, you could find out of the price of taking your calipers to anywhere that has 338 rum and measuring shoulder diameter --

but, again, iirc, the 338 imperial is much longer than the rum ... same trip, measure case, not oal, length

yes, its possible to take a 338 winnie take off barrel and rework to which ever you like, either 338 rum or 340w


i would recommend a chamber cast for precise measurement

This is a very rare cartridge that the rifle is chambered in. I don't know what a 338RUM or 340Wby will do that your rifle won't do as is if you can get it to run. I found one load on the internet for the 338Imp using 225 grain Accubond over Re22 powder giving around 3300 ft/sec. I am no gunsmith but I have fixed some issues on firearms and wish I was closer to you so I could see what you are dealing with.

If you are dead set on going to a different cartridge you should seek a qualified smith to see if he could rechamber with a little barrel set back or have to rebarrel.

Well, color me old and forgetful, or maybe losing it, but I'm sure I've rechambered a couple 338 Imperials to 338 Ultra Mag.

I can't find a drawing of the 388 Imperial, but if memory serves the Ultra Mag is about .006 larger at the base than the Imperial. The Imperial is about .004 larger at the shoulder and the Imperial is about .040 longer to the shoulder.

It seems to me that you have to knock about 1/2 inch off the thread extension to make it work. If the coconut that installed the barrel used a relief cut at the shoulder you would have to knock off the entire thread extension. All this would hinge on having enough chamber area to work with. I would also find a drawing and double check it. My thinker doesn't work like it used to and I was just complaining to the owner of WGP that I was on my 20th barrel job since Christmas so barrel and chamber work gets kind of bunched up in my widdle-pea-brain.

Red Neck from 24 hour campfire sent me this to study any thoughts about going from imperial to RUM with this?

Thanks Brad

That's kinda what I remembered. It looks like you have to push it forward at least .050 to clean up the shoulder. So that's not a problem. There would be a difference of .004 inch in your shoulder diameters. The Ultra Mag has a body taper of about .010 per inch so moving everything forward 1/2 inch should clean up the ring. (providing that the original Imperial Magnum chamber is to spec.) It wouldn't hurt to throw a chamber cast just to double check the dimensions. Standardized wildcats do tend to vary a lot.

It all comes down to whether or not you have enough main chamber area available to support moving it forward. And whether or not the original extension has a relief cut on the shoulder of the barrel or not. If there is a relief cut its going to be a full inch.

It seems to me you could circumsize most of the chamber, rechamber it to whatever 404 based magnum you desired, still have a 25 inch or so barrel, but for hunting normal elk under normal condidions a 24 inch barrel would be more desirable..Just my two bits without available specs or the rifle in hand to play with.