Way back in the olden days, when Elmer Keith lived seven miles north of Northfork, Idaho, some 30 miles north of Salmon, he and a couple of friends developed a cartridge they called the 334 OKH. Ironically, the ranch Elmer Keith used to live on above Northfork is located on the opposite side of the road from mile marker 334 on U.S. 93. Elmer died on Valentine's Day in 1984. The OKH stood for O'Neil, Keith, and Hopkins. The cartridge was essentially a 375 H&H Magnum necked down to accept 0.334-inch-diameter bullets. At the time, there were still third-inch bullets being made by the British, while Barnes was the first person in the United States to do the same. Because of Elmer Keith's growing fame and reputation as a writer, the OKH became better known than similar developments such as the .333 Barnes Supreme, which also used the belted 375 H&H case but was also "blown out" for greater powder capacity. Even P. O. Ackley got in on the fun, by giving his version of the blown-out .333 Magnum Improved his now famous 40-degree shoulder.
And then there's Roy Weatherby, who must have been in a conservative mood when he passed the chance to do more of the same. Roy waited until 1963 to introduce the best of the lot; the 340 Weatherby Magnum with its very effective double-radius shoulder. It, too, is based on the 375 Holland & Holland Magnum, a belted cartridge that dates back to 1912 and is still going strong. Why is it the best? That's just an off-the-cuff opinion, meant to stir up a little controversy. But I can tell you this... I've had more than a few 338 Lapua rifles in my hands, dating back to when they weren't all the rage, and from my bench the 340 Weatherby consistently is more accurate in rifles of equal quality, and almost identically as powerful even though it has notably less case capacity.
Weatherby's 340 came along just five years after Winchester introduced the excellent 338 Winchester Magnum, and that reason more than any other is likely the one that finally got Roy to fill the gap between his legendary 300 Weatherby Magnum and the very powerful 375 and 378 Weatherby Magnums.
The 340 Weatherby Magnum rifles most often have a 10-inch twist, so they can stabilize a 300-grain Sierra MatchKing. I have found that somewhat lighter match bullets, especially the 250-grain MatchKing, shoot best out of my rifles. I have everything from a light and handy Cooper sporting rifle to a fine Ed Brown Marine Sniper in 340, with others such as a Weatherby Accumark and a Fibermark in between. They all shoot extremely well. The worst shooting 340 Weatherby I ever owned was a Japanese-made Mark V Deluxe. It shot a little under an inch, and was beautiful. The rosewood forend tip and grip cap was truly a dark pink rather than red, and the walnut stock was also a lighter-than-usual tone. Highly figured, and everybody wanted it. Somebody finally made me a deal I couldn't refuse, and I regret it to this day.
Some people, usually the jealous types who want but don't own a Mark V, crab about the stock design. It's easy to find the whiners on the internet. Problem is, they simply don't get it. Weatherby could have gone in any direction with the stock; he started with a blank sheet of paper and a superior intellect. Here's the deal... the Weatherby stock with its Monte Carlo profile, and a cheekpiece that has proper draft for sliding gently away from the "cheek weld" upon recoil, is far more comfortable with heavy cartridges than, say, a classic stock design. And look when he designed the stock; the later 1950s. Remember the exaggerated style of the cars from those days? And what do so many people still love? The '57 Chevy, fins and all. Quite frankly, I sincerely hope that Weatherby never changes the beautifully effective stock design of the Mark V Deluxe.
What can the 340 do? For starters, it is soundly more powerful and flatter shooting than the 338 Winchester Magnum, and the 338 Winchester Magnum is a wonderful cartridge. Next, no other commercial .338 caliber cartridge has more than a paper-thin advantage over the 340 Weatherby on paper, and no practical advantage whatsoever in the field. When you're seeking the best in a light heavyweight, and you get to the 340, you've gone about as fer as you can go. (Oklahoma! fans will understand the "fer.")
In the recoil department, my 70-plus-year-old body can stand up to it, as I find it to be in a league with trim 300 magnum rifles. You know you've pulled the trigger on something, but I see it like this: The rifle is going to punch you either way, whether you flinch or not, so why flinch? I've used this logic throughout my life, and it works for me.
As far as game goes, the 340 will reach out with flat trajectory and great authority. For moose in the northwest, I tend to recommend very well constructed heavier bullets such as the Swift 275-grain A-Frame. It will plow through muscle and bone from any angle. In Africa, Swift A-Frames are equally effective on game such as eland. For longer shots at somewhat smaller game, such as greater kudu, a 225-grain Hornady, or any of many other choices, should be just fine. I mention the 225 Hornady because a friend took a record book greater kudu at a measured 541 yards a few years back with that combination. Neither he nor I recommend such long shots, but his health prevented a closer stalk, and his demonstration of his shooting skills to the professional hunter (PH) resulted in permission to take the shot. The trophy mount now hangs here in the shop.
The 340 is also effective for considerably smaller game, such as African antelope and the pronghorn of North America, and various deer. Most bullets just punch through with partial expansion and very little meat loss. For elk, the cartridge is a classic with 225- to 250-grain bullets.
If you wake up some morning with the overwhelming urge to shoot 225-grain bullets at 3000 fps, as fast as 180 grainers out of most 300 magnums, now you know what you need.