.240 Weatherby Magnum – the ultimate 6mm cartridge

You don’t hear much about it, but the .240 Weatherby Magnum deserves more recognition. It’s a going-hell-for-leather 6mm cartridge that shoots flat and hits hard enough for big-game.

The .240 Weatherby Magnum is one of my favourite cartridges. It’s a high velocity small-bore round that’s a lot more potent than most shooters could ever imagine. It has enough case capacity to drive 100gn .243-calibre bullets at 3400fps providing stretched string trajectory, accompanied by surprisingly fine accuracy. 

A bit more slender than the .30-06,the .240 Magnum shares the same case-head size, and length – 63.5mm (2.500”), but headspaces on the belt in charactaristic Weatherby fashion and features the traditional Weatherby double radiused shoulder. The .240 Weatherbycase has minimum taper and holds 65 grains of water while its .243 counterparts, the .243 Winchester and 6mm Remington, hold considerably less – 54 and 55 grains respectively. While this 6-mm sizzler registers high velocities, .243 bullets are not heavy and hence recoil is light making the rifle a real pleasure to shoot. 

Modern slow burning powders are needed to realize the full potential of the ample powder capacity of the .240 Weatherby. I found that Reloder 22 powder, specially developed for large volume cases gives top velocities in the .240 with 2000 to 3000 psi lower chamber pressures than either AR2209 or AR2213sc. While both of the latter powders also do a fine job, I’ve found Re-22 remarkably consistent from one lot to the next which is a large boon to reloaders who cannot or don’t want to buy powder in large quantities. Sometimes a change in canister lots of various powders will require compensation in a grain more or less in the reloader’s charges. If one lot of powder happens to be a little hotter than normal, it can prove embarrassing to the reloader who is already working just shy of top pressure levels.

Alliant recommends against using markedly reduced loads with Re-22, because of the danger of detonation (Secondary Explosion Effect), present with ultra-slow burning powders. I’ve found that a 10-percent drop from the maximum loads recommended in most manuals to allow for variations in rifle, brass, bullets, etc., might be enough to cause an unwanted “detonation.” In fact, I know of one .240 rifle that blew up because it was loaded too light using Re-22! When working up loading data in a given rifle, lacking any signs of excessive pressure, you can progress to maximum loads if desired. The mean pressure for Weatherby factory loads is 54,000 psi.

The .240 Weatherby has often been touted as a varmint cartridge. I honestly can’t see it in that role, but I think that it is the best commercial long range dingo cartridge going, particularly if you want to reach way out across the western plains to tag some cunning old stock killer. The factory 70gn bullet streaking along at 3850fps or handloads with the 75gn Barnes TSX or the 75gn Hornady V-Max at 3700 fps will do a great job. 

My Maddco-barreled F.N Mauser is superbly accurate for almost any predator situation. It averages 1/2-minute groups with the lighter bullets and has often planted three 100gn Lapua bullets into 1/4 MoA. Besides being a great predator calibre, the .240 Weatherby Magnum is one of the most deadly cartridges I’ve ever used for deer, with the single exception of sambar. I’ve taken probably a dozen rusa with the 100gn Lapua and they all dropped in their tracks. I’ve also shot a number of fallow and chital with the Hornady 95gn SST ahead of WMR ball powder at various distances from about 100 to 350 yards. Not one of them moved out of their tracks. 

It’s the mild recoil, light rifle aspects of the 24-bore, coupled with its sudden stopping ability that makes the .240 Weatherby so attractive to many deer hunters. Certainly the .243 Winchester and 6mm Remington have proved reliable deer and a antelope stoppers in the U.S and I heard of a hunter who killed three grizzly bears and two elk with the .243 back in 1967. I wouldn’t recommend any 6mm for game that size, but it certainly gives an indication of the giant killer potential of the calibre.

My friend the late Les Bowman, when he was outfitting and guiding in Wyoming told me that back in 1968 when he got one of the first Mark V rifles in .240 Weatherby calibre he took an antelope at 150 yards and a mule deer buck at 300 yards with his first two shots at game using the 90 and 100gn factory loadings. Later at the Y.O Ranch in Texas, he took a blackbuck at 200 yards with the 100gn Norma bullet. He swore by the .240 for being a sudden killer on everything from antelope to elk, but I draw a line at using the .240 for wapiti and much prefer the .270 Weatherby for that majestic animal.

Actually, there are several 6mm wildcats that duplicate the performance of the .240 Weatherby. The 6mm-06 was the first, the 6mm-284 another. I could find no material difference between the 6mm-06 and the 6mm-284 when I tested them and both rounds have proven very successful when chambered in a great many custom rifles. 

I dismantled and checked .240 Weatherby factory  ammo in both 85gn and 100gn weights. Cases showed very uniform weight, except for an infrequent one that varied by .03 grains. Powder charges ran plus or minus .2 grain either way. Bullets used are the Hornady 87gn spire point and Nosler 100gn Partition and run within .5 grain variation. With maximum test loads cases grew to maximum length after three firings. After I settled for good velocity using optimum loads (3350fps with the 100 grainer), cases lengthened 0.010” after 10 firings. 

Chronographing Weatherby factory ammo in my F.N rifle showed the 87gn Interlock bullet going through the Chrony at 3425fps ; the 100gn Partition at 3280fps. Weatherby lists those loads at 3448 fps and 3222 fps most likely from a 650mm barrel. Evidently, my rifle loses little or no velocity from its 610mm Maddco barrel.

On the whole, the .240 Weatherby is an easy cartridge  to reload for and there’s a host of bullets including a good many premium ones. For my own use, I see no benefit in loading bullets lighter than 90 grains and usually stick with a nicely pointed 100 grainer or the Speer 105gn spitzer. But my favourite deer bullet is the 100gn Lapua (not a Mega). This is a slim spitzer type with a tiny bit of lead barely visible at the small tip and a cannelure. Weight variation  is .2 grain. It holds together at high velocity and gives moderate expansion and achieves deep penetration. Typical of its performance was a shot I took at a fallow buck standing broadside at about 115 yards.The bullet made exit after passing through both shoulders. 

I’ve found this 100gn Lapua bullet to be ideal with good expansion and high retained bullet weight, at all normal ranges. I have also used the 100gn Nosler Partition which develops a bit higher pressure, therefore higher velocity by an average 30 fps with the same load, than the Lapua does. 

On a trip to the Gulf country I knocked off a number of rusa stags and a large number of wild boars at ranges out to 300 yards, each dropping to a single 100gn bullet. One large boar was running away from me at an angle heading for a patch of brush. Shooting from the sit, I swung the crosswires out ahead of his snout and pressed the trigger.  I heard a “whock” signifying a hit. The pig did a somersault and piled up just a few metres short of cover. The 100gn Lapua bullet had hit him in the right hindquarter, went on through and passed through the paunch and into the chest cavity, wrecking the heart and lungs. I couldn’t have asked for any better bullet performance.

All my reloads are sparked off using magnum primers which are best for large volume cases using hefty doses of slow-burning powders. These include Federal 215, CCI-250, WLRM and Remington 9-1/2. Cases for the .240 are, of course, limited to Weatherby and Norma whuch are the same thing. Don’t bother trying to make .240 cases by swaging a belt on .30-06 brass, it’s simply not worth going to all the trouble. 

As mentioned previously, the best all around powder seems to be Reloder 22. It appears to give less pressure and be more consistent than AR2213sc. The first .240 I had, a Mark V Lightweight, showed a liking for the 100gn Hornady bullet. This rifle did its best with WMR Ball,powder, shooting tight groups with the recipe accompanied by very high velocity. WMR is no longer available, Winchester’s new Supreme 780 has relaced it, and produces practically the same results. In my F.N rifle 54gn of Supreme 780 drives the 100gn Lapua at 3350 fps compared with 3306 fps with an equivalent amount of WMR. 

The rifle shoots three 90gn Lapua bullets into an average .55 group with those bullets leaving the muzzle at 3425fps ahead of 55gn of AR2213sc. Another very accurate load with the same bullet uses 53gn of AR2209 for 3395 fps. An excellent mild load with the 105gn Speer spitzer was 54gn of WMR for 3265 fps.

All of my charges of slow powders are high density  loads that fill the case to the base of the neck. Weatherby recommends holding cartridge overall length to 3.075” (78mm). My loads with light bullets average 77.8mm but the majority of them are 78.5mm. One exception being the long, slim 95gn Nosler Ballistic Tip which allows a cartridge O.A.L of 80mm. 

Let’s take a look at the trajectory of the 100gn Lapua game bullet given a velocity of 3390 fps at 3 metres from the muzzle, and with a published B.C of .287. With a plus  or minus rise or fall of 100mm from line of sight, this computes a maximum point blank-range of 316 metres.  The optimum zeroing distance is 271 metres or 83mm high at 100 metres. Sighted-in this way, by using the 450mm from the top of the deer’s back to the deer’s brisket rule of thumb, I only have to hold a bit high on deer’s chest to  score a killing shot out to 400 metres. I like to keep my shots under 300 metres, however, if I don’t mind straining the barrel a little, the .240 has enough velocity to compensate.

That 100gn Lapua bullet is still packing 1192 ft/lb of energy out at 300 metres, that’s considered adequate for deer. And the remaining velocity of 2317 fps is enough to ensure proper bullet expansion. Even at 400 metres, the figures are 2012 fps and 898 ft/lbs of energy for the .240, hardly enough power for deer unless the bullet is placed exactly right.

There are other more streamlined bullets for long range shooting eg the Lapua 100gn Scenar bullet, with the outstanding B.C of .530 which would no doubt have  a slightly flatter trajectory and give superior ballistics downrange, but it’s primarily a target bullet. You could pick a plastic-tip bullet, like the Nosler Ballistic Tip or AccuBond, the Hornady 95gn SST, or the Swift 90gn Scirocco. If you want to take a rugged red stag at extended range, develop your load accordingly. First, choose a streamlined, controlled expansion bullet that is designed for game, not varmints. A good many bullets in this diameter are varmint bullets. If you stay above about 90 grains in bullet weight, you are generally getting a tougher bullet. 

Second, load for as much muzzle velocity as you safely can. I find a 100gn bullet at 3350fps rather than 3400fps extends barrel life somewhat. Pick an optimal powder such as Winchester Supreme 780 which is easier on chamber throats than stick type powders, and gradually work up from the starting load printed in your manual. A 600mm barrel is better balanced and than a 650mm barrel and loses very little velocity.

Recent tests with Barnes 85gn TSX boattail bullet driven at 3,445 fps by 54gn of AR2213sc produced 3-shot groups around .60 MoA and they proved sheer dynamite on ferals. With maximum point-blank range of 281 metres, trajectory is 81mm high at 100m, and only 36mm low at 300. Energy at 300 & 400 metres is about the same as with the 100 grainer. For an all-around bullet this one’s a real contender. In all test loads, there was no sign of excessive pressure either by measurements taken on the case head or the appearance of the primers.

The .243 and the 6mm Remington are excellent cartridges when it comes to accuracy and efficiency in hunting rifles, but the hunter who wants the ultimate in 6mm chambering, with factory ammo available should definitely consider the .240 Weatherby.


This article was first published in Sporting Shooter, August 2010.




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