I have a set of .338-378 weatherby magnum RCBS full length, trim and case forming dies. I also have a shilen barrel for a ruger #1 in same caliber. What in the hell can a guy do with those things?

Sounds like a good reason to build a custom rifle! Otherwise if you don't want a #1 in 338/378 put them up on Ebay or gunbroker or something.

It's not that I don't want another custom rifle. It's just how do I go about it and maintain the current caliber.

I was looking at load data for this round.

250 gr bullet at 3300fps!!!!!!!
over 5000 lbs energy at the muzzle!!!!
64 lbs of felt recoil!!!!!

It seems to be unpleasant at either end of this one.
I got to make this happen.

Just a brief note of caution: I think the factory load is a 250-grainer at 3050 fps out of a 26 inch barrel. 3300 fps might be an excessively high-pressure load, at least without much more barrel length.

I'd build a .338-.378 in a second, but before you do that, do check and see how close the .338 RUM is. The RUM is going to be a lot easier to buy and to own.

Clymer's stock reamer has a long throat. If you want to be close to the rifling and fit in the magazine, you might want a shorter throat. The Sierra GameKing has very little full-diameter bullet left in the neck if you load it close to the rifling.

I have used WC872 and IMR 5010 in .338-.378. IMR 5010 is a bulky stick powder, and you get a slightly compressed load with a long round and factory ballistics. If you want to shoot out of a magazine (yes, I know the Ruger No. 1 is a single-shot) you might be better off with WC872. Your starting load is 100 grains with either powder. Develop your loads with a chronograph. You might have to back your chronograph up if the muzzle blast bothers it. Ten yards is good. Work your loads up carefully. Take a few weenie starting loads to the range for your friends' first shot, max loads if you have reason to have them. The difference is impressive.

I would build that rifle heavy with a slightly long length-of-pull if you contemplate shooting positions from a bench or prone. You are okay sitting, standing or kneeling, but in positions where you can't back up easily, the rifle will come get you. Get a Pachmayr F990 recoil pad and don't put your eye too close to the scope. Never pull the trigger until you have considered where your eye and/or shooting glasses are behind the scope (five, count 'em, FIVE inches behind the scope from bench or prone). Don't expect to do well immediately. It takes a lot of discipline to shoot a .338-.378 well.

Some Ruger No. 1's shoot erratically. One of the problems is the fore-end hanger. It's sort of cantilevered on the front of the action. When you pull the trigger the fore-end rattles against the barrel and the bullets go everywhichaway. The solution is to put a pillow block on the bottom of the barrel, contoured to the barrel, and with a depression on the bottom to match the setscrew that goes up through the hole drilled and tapped in the end of the hanger. Turn up the setscrew tension a little, and the hanger and the fore-end and the barrel vibrate together and you get shooting nearly as good as the barrel. Use Loc-Tite or glue on the setscrew to keep it where you need it. Ross Seyfried wrote an article with pictures on doing this that was published in Guns and Ammo.

Keep in mind the velocity exceeds what bullets were designed for, until recently. Bullets of moderate construction may blow up on impact. If you are going to shoot a game animal, use a tough bullet.

Get .338-.378 factory brass. Forming cases from .378 Wby brass is unrewarding work. Either way, your neck wall thickness should be the same, but a prudent person would check. Because Weatherby adopted the wildcat, they kept the neck wall thickness obtained by necking down the .338-.378 without neck turning for their factory brass. Keep an eye on your case length too.

I did it the hard way .I bought 1600 rounds of 416 weatherby from Graf and son on sale $32 .I deloaed it then used the woodleigh bullets in my 416 rem mag the Norma MPR in alot of calibers .I have to buy 378 weaherby dies and neck it down twice .Its a big job just to deload it.My brass turned out good .Its funny it shortens when I shoot it .I love both of my Weatherby 338-378s they are awesome !

Count me in as another happy .338-378 Weatherby Magnum owner. Mine is an Accumark and I'm real pleased with it's accuracy. I'm also a fan of WC-872 Powder for this caliber. The .338-378 is king of the .338 bores. Not even the .338 Lapua can touch it. Bill T.