Way back in the day, in my teens and early 20’s, (when Elmer Keith lived but on my bookshelf, and the likes of “Hatchers Notebook”), I was always facinated by the cartridge he called the 334 OKH. OKH stood for O’Neil, Keith, and Hopkins. The cartridge was 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, and built his version of the blown-out .333 Magnum Improved his now famous 40-degree shoulder or “AI” Improved Calibers.
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 Magnum consistently is more accurate in rifles of equal quality, and almost identically as powerful even though it has notably less case capacity, so the efficiency was a proven fact despite the new generation moving away from belted Magnums to that of the 300 and 338 Remington Ultra Magnums.
(those that know me also know I love my RUMS!) This being said the fact remains the 340 Weatherby Magnum is still far more efficient, belt and all and burns considerably less powder and runs much better than the .338 Win. Mag. in terminal ballistics way out to 600 yards or more.
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. On paper the 378 is far more powerful than the 375 RUM and that is also a proven fact due to the radius shoulder where efficiency is born.
The 340 Weatherby Magnum rifles most often have a 1:10-inch twist, so they can stabilize the 300-grain Sierra MatchKings for target or two-legged quarry to the mighty 300 Grain Nosler Accubond Bullet for hunting 4 legged quarry…
I have found that somewhat lighter match bullets, especially the 200 and 250-grain bullets also shoot well out of my Custom TC Encore in 340 and also my Custom Remington 700 in 340 WBY Mag. I have everything from a light and handy 340 Weatherby Magnum sporting rifle in a 8 lbs. TC Encore to a 12.5 lbs. TC Encore Target Version including my 338 Lapua Magnum pulverizer the M40M1-A2 Marine Scout Sniper in 340. I got rid of all but one of my Weatherby 340’s and kept the Laser Mark Sporter. My M40M1-A2 340 will pulverize the 338 Lapua Magnum at any distance well out to 1,200 yards. Proven Fact.
They all shoot extremely well. The worst shooting 340 Weatherby I ever owned was an American-made Mark V Deluxe. It shot a little under an inch, and was beautiful but a hunter, not a shooter…
My VVCG – CBJ Precision 340 Custom .338-.340 – Custom Chamber 340 TC Encore https://media.licdn.com/dms/image/C4E12AQGsTUajNQXWHA/article-inline_image-shrink_400_744/0?e=1544659200&v=beta&t=DXjJDZp-woyMjSmDGlIJNMRQpDSrnKutjdxiSm9g-Ts
Some people, usually the jealous types who want but don’t own a Mark V, whine about the belted magnum case as being “outdated” or that it is chambered typically only in the MARK V Actions… (yeah, that is why I build now 100% of the Weatherby Calibers in the “BETTER” REM 700 Long Actions)… whiners on the internet prevail especially at ROKSLIDE Web Forumn where everyone is a DIY Expert Gunsmith that know ZERO about performance of long range terminal ballistics…they all claim to be experts… PERIOD!
Problem is, they simply don’t get it. Problem is the web-guys start out shooting on paper and a superior intellect, (or so they think) when they have no idea of the 340’s capability in a superior rifle to handle the performance. Fact is, the 340 will always outperform the 338 Lapua Magnum and that comes from my 40+ years of experience… and fact in building some of the fastest .338 calibers on the Planet.
What can the 340 WM really 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 far as you can go and even the 338 Excaliber and 338 Allen cannot out perform the 340 Wby. Mag.
I run a 5 Port BIG BORE Brake and the 340 Wby. Mag. is as tame as a 30-06 shooting 150 grain projectiles. That is just a fact.
As far as game goes, the 340 will reach out with flat trajectory and great authority over a 300 Win. Mag., 338 Win. Mag. or 338 RUM. For Elk, Bear or Moose I tend to recommend very well constructed heavier bullets such as the Swift 275-grain A-Frame or the 300 Grain Accubond by Nosler. 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 tend to recommend the 225 to 250 Grain Projectiles in the 340 for skills to the professional hunter (PH) for most all other hunting at any ethical ranges and their trophy rooms prove the fact the 340 is king of the .338 Calibers. PERIOD!
The 340 is also effective for considerably smaller game, such as 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 3,300 fps, as fast as 180 grainers out of most Monster 300 magnums, now you know what you need in order to pull that off. But you need it built by us! Bayou Advanced Weapon Systems, LLC.
Corey B. James
Custom REM 700 Accurized Long Action, Trued Action w/ 27″ SENDERO Contour Stainless Barrel Fluted (6 flutes), blackened spiral flutes (27″ barrel length without brake), 5R, 1:10″ Twist Rate, BIG BORE 5-port brake threaded 5/8″x24″, REMAGE NUT, Recoil Lug, .202″ Precision Ground, 338-340 Weatherby Magnum Custom Chamber — 300 Gr. AB Noslers run at nearly 3,490 FPS – built better by: Bayou Advanced Weapon Systems, LLC and CBJ Precision http://precisionengineeredrifles.com/services