338-378 WBY Mag

[Ironworker]

Problems . Bought a Mk V accumark used under 50 rounds thru it( Came with new and once fired brass,Dies and 2lbs of Retumbo and Leupold scope I've since sold,deal of a life time,couldn't pass it up). Previous owner used Leupold Standard rings ,after 40 rounds recoil destroyed those rings. Installed a Ken Farrell industries rail on it designed for WBY Mag.But rifle shot hard right,so I installed Burris signature rings with off set shims.I was then able to zero rifle. The directions with Farrell rail said recheck screws and recoil lug screw after first few shooting sessions. I noticed a few shots would be on the money and then next group was way high and to the right !!! So I re-checked screws and they were a little lose. Directions said the rail is settling in. So back to the range tomorrow,the factory brake is fine for shooting standing up,but not off a bench . I bought a Terminator 5 port T4 and it was unbelievable the recoil reduction,but oh the muzzle blast was huge. Anyhow any one have experience with these big boomers,any suggestions ? Looking back I wish I save my cash and bought a 6.5 PRC ,but I love guns like us all.

 

[dkhunt14]

The 338-378 was really not made for sitting down and shooting alot of rounds off the bench. Another thing, depending on load and rate of fire, I have seen throats completely shot out in 500 rounds. It is basically a hunting gun and not made to shoot hundreds of rounds. Years ago they used them in 1000 yard BR but they disappeared many years ago. Barrel life and accuracy and too much recoil made it fade away. Matt

 

[MikeMcCasland]

I've got a buddy who has one, and is on his 4th or 5th barrel. They're absolute beasts, and quite frankly I don't enjoy shooting it, or being around it. That said, it's great for killing the larger african exotics imported into Texas.

Like you, he had scopes moving in the mounts until until he put a brake on it. He's got an unbraked 8mm-378 that's also hell on scopes.

They can be very accurate, powders like H870, H869, Retumbo, 50BMG are what you want. Brass is stupid expensive, so you'll need to be bumping shoulders ever so slightly, and annealing to get as much life as you can out of it. You'll also want to only buy in kegs; 1lb canisters are worthless for something that eats 115gr at a time.

Probably about 10 years ago I watched him shoot a Barnes 160gr .338 (X-bullet I think) over a chrony at 4,000 FPS. That said, the barrels don't last at all. Your rate of fire needs to be exceedingly slow; if you do that, you'll be lucky to get ~1,000-1,200 accurate rounds out of it.

 

[wboggs]

I build one on a magnum mauser action and krieger barrel for hunting in the 70's when it was a wildcat. Had to neck down .378 cases and inside neck ream them. Back the H870 was the powder. I got about 3100 from 250 gr noslers from the 26" barrel. Accuracy was about 1 1/2 " for 3 shots at 100. Weight was 11 # with a leupold hunting scope and mounts. Back then I could carry it on mountain hunts in the Yukon. It was a deadly combo and I took a lot of game but recoil was fierce on the unbraked rifle and it wasn't worth the expense and trouble. Finally, I converted it to a .416 rigby and sold it.
In my opinion, it is an expensive play toy and you should view it as such.
Bill

 

[Rdlningcltchdmpr]

Us 869 powder . is the ticket.

 

[Rust]

While not exactly the same, I have a lightweight mountain rifle based on an M70 chambered in .300 RUM and it is not braked. Recoil is worse than my .338 Lapua (with brake removed) or .416 Rigby (no brake) just because it's so light. It ate the first two scopes. Mounts were a problem so I used an old trick, the mounts and screws are glued in using high shear strength golf club epoxy. The judicious use of a heat gun will allow removal of screws and mounts. Rings are Ken Farrell four screw which have been carefully lapped in. The scope is now a Leupold simply because of the guarantee.

Only problem is once you get past 65 ridge running and shooting with a big magnum isn't nearly the fun it used to be.

 

[Ironworker]

I once had a Rem 700 in 300RUM and yes that dang rifle kicked very hard,in fact harder than this rifle..... I have a Ken Farrell WBY G force rail on it. Directions say check it every time after first few shooting sessions. Sure enough I'd get it zeroed with a few shots and then all of a sudden next few would be off. So re-checked screws and they had room to be tightened. Directions say that's the base settling . Well when to apply lock tight ? How will I know base has finished settling ?

 

[Evan]

Short of epoxy, you could try blue loctite. I don't buy the "rail settling"; how does that work?

Good luck. Doesn't sound like fun to me though.

 

[Kingfisher]

Late to the party. I'm the *cough* friend Mike mentioned above. I've got an Accumark that was a factory 30/378 that I rebarreled to 338/378. The first 2 338 barrels were Shilens. Both 29" #17's with no brake. I had some initial teeth cutting issues with scope/rings etc. moving but after moving away from standard bases and going to rails and beefier rings (it currently has Leupold Mark IV's) scope hold is a non-issue. I got the Mark IV's on clearance and they've been well worth it, especially considering what a hammer that thing is. I tried the Signature rings with the shims on the 338 and had a couple of issues... movement was one of them. The 8mm/378 is built on a Brno ZKK-602 (rechambered 8x68s). It's a magnum sporter setup, and with the hogback stock it's a hammer. A fair bit worse than the 338. For that one, CZ rings seemed to work well enough. I should add that all the rings, mounts, etc. all end up with a healthy dab of blue Loctite.