Compared: The .240 Weatherby Magnum and .25-06 Remington
By Chuck Hawks
The case capacity of these two cartridges is very similar. The .25-06 was created by simply necking the .30-06 case down to accept .257" diameter bullets. The .240 Weatherby case is essentially a belted version of the .30-06 with a Weatherby double radius shoulder that accepts .243" diameter bullets. Hence, what we are really comparing here are the.243 (6mm) and .257 bullets when fired from similar size cases.
When introduced, the .243 Winchester and 6mm Remington put the blocks to the existing .250 Savage and .257 Roberts. Some knowledgeable shooters think that the .257 Roberts remains the best and most versatile cartridge among the four, at least for hunting CXP2 (medium) game, such as deer. However, the 6mm's are undeniably more suitable as long range varmint cartridges and therefore probably better varmint, small predator and medium game combination cartridges.
The big case .240 Weatherby Magnum and .25-06 Remington can be used for shooting varmints with light for caliber bullets widely available to reloaders. However, their muzzle blast, recoil and relatively rapid barrel erosion are really not conducive to the high volume shooting and use in semi-populated areas that characterizes so much varmint shooting. Remington doesn't even offer a dedicated varmint load for their .25-06, but Federal (alone of the big four U.S. ammo companies) offers an 85 grain Nosler Ballistic Tip-Varmint bullet at a muzzle velocity (MV) of 3550 fps.
Weatherby offers the dual-purpose 87 grain Hornady Spire Point bullet in a .240 factory load at 3523 fps that can be used for varminting, as well as hunting the smaller species of CXP2 game. Zeroed at 300 yards, that load rises 3.4" above the line of sight at 200 yards and drops only 8.4" at 400 yards.
This is very comparable to the trajectory of a .220 Swift with a 55 grain boat-tail spitzer bullet loaded to the maximum (3800 fps). Of course, the .220 is considerably more pleasant to shoot than a .240 WM or .25-06, which underscores the problem of using these big case cartridges for shooting varmints. The .220 Swift, designed specifically for maximum range varminting, is normally a better choice for the purpose than either the .240 or the .25-06.
That leaves medium game hunting the primary focus of this comparison between the .240 and .25-06. Because of their strong, belted case heads and the very strong Weatherby Mark V action, Weatherby cartridges are typically loaded to somewhat higher maximum average pressure (MAP) than conventional cartridges. For example, the SAAMI standard MAP for the .25-06 is 53,000 cup and for the .240 WM it is 53,500 cup. Not a huge difference, to be sure, so we can use factory load ballistics for this comparison.
For hunting CXP2 game, the most popular bullet weight in Weatherby factory loads for the .240 is 100 grains. Weatherby offers the excellent Nosler Partition bullet in that weight, so this is the load we will use for comparison.
In the .25-06, the most common bullet weights factory loaded by Remington, Federal, and Winchester are 100, 115 and 120 grains. Since Federal loads the 115 grain Nosler Partition bullet, this is the .25-06 load we will use for comparison.
The two Nosler Partition bullets are similar in shape (flat base spitzer) and terminal performance. The ballistic coefficient (BC) of the .243/100 grain Partition is .384, while the BC of the .257/115 grain Partition is a similar .389. We will compare these factory loads in velocity, kinetic energy, trajectory, sectional density (SD), cross-sectional area, killing power, recoil and the availability of rifles and ammunition.
Velocity is the most important component of energy. It also decreases bullet flight time and hence flattens trajectory. Some hunters feel that high velocity per se contributes to killing power through increased shock effect, but that has been difficult to prove scientifically. Here are the velocities from the muzzle (MV) to 400 yards in feet per second for our selected loads.
As these figures show, the .240 is considerably faster at all ranges. This bodes well for its showing in the energy and trajectory comparisons to come.
Kinetic energy is a way to measure a bullet's ability to do work. The "work" in this case is expanding and penetrating deep into a game animal to destroy the maximum amount of tissue and kill quickly.
Energy is an important factor in cartridge performance and killing power. Kinetic energy is a good indicator of the power of similar rifle cartridges, such at the .240 Weatherby and .25-06 Remington. Here are the energy figures in foot pounds for our selected loads from the muzzle (ME) to 400 yards.
Since about 800 ft. lbs. on target with a suitable bullet is the accepted standard for humanely harvesting CXP2 game, it is clear that both the .240 and .25-06 are capable long range, medium game cartridges. The .240's higher velocity gives it the advantage in kinetic energy, despite the .25-06's heavier weight bullet.
The .240 and .25-06 are flat shooting cartridges. The flatter a bullet shoots the less the shooter needs to compensate for bullet drop and the better his or her shot placement is liable to be. The following trajectories (in inches) are computed for the maximum point blank range of each cartridge/load (+/- 3") and assume an optical sight mounted 1.5" over bore and standard atmospheric conditions. Bullet rise and fall in relation to the line of sight are given from 100 to 400 yards.
The flat shooting .240 Wby. has a MPBR of 326 yards when zeroed at 277 yards. The .25-06 has a MPBR of 293 yards when zeroed at 249 yards. As these trajectory figures show, the .240 clearly wins the trajectory comparison.
Sectional density is defined as the ratio of a bullet's weight in pounds to the square of its diameter in inches. SD is important because the greater the SD, other factors being equal, the deeper a bullet's penetration. Penetration is an important factor in the length of the wound channel and the amount of tissue disrupted. Obviously, to kill quickly a bullet must have sufficient penetration to reach and disrupt the animal's vital organs. Here are the SD numbers for our comparison bullets.
The .25/115 grain bullet has a modest advantage in SD compared to the .24/100 grain bullet. However, it is not decisive and both are well above the .225 SD considered excellent for CXP2 game. Similarly, both are well below the .260 SD recommended for small bore bullets used for hunting CXP3 game, such as elk, and neither the .240/100 grain nor .25-06/115 grain factory loads are recommended by their manufacturers for use on CXP3 game.
Greater cross-sectional area means that, other factors (such as the percentage of bullet expansion) being equal, the fatter bullet should create a wider wound cavity, damaging more tissue and hastening the animal's collapse. Here are the cross-sectional areas of our two bullets in square inches.
It is obvious that a .257" diameter bullet has a greater cross-sectional area than a .243" diameter bullet. That .014" difference in diameter has a significant effect on frontal area. It was a foregone conclusion that the .25-06 would beat the .240 in this comparison.
There are various ways to estimate killing power, none of which are entirely accurate. Bullet placement is the most important factor in a cartridge's effectiveness on game and it is a function of the shooter's skill and judgment, not the cartridge itself. The construction and performance of the bullet is also very important, which is one of the reasons we have chosen to compare bullets of the same design (Nosler Partition).
An attempt to include at least some of the factors relevant to killing power (primarily impact velocity and bullet weight) is the Optimum Game Weight (OGW) formula developed by Edward A. Matunas and published in the Lyman 47th Reloading Manual. Matunas assumed that bullet design and placement are adequate for the task at hand, which in the case of our comparison loads, they are. The numbers below indicate the size of animal (live weight in pounds) for which each load is presumably optimum at ranges from the muzzle to 400 yards. (For more on OGW, see the "Expanded Optimum Game Weight Table" on the Tables, Charts, and Lists Page.)
While the .240 has an OGW advantage at all ranges, it is not decisive and the live game weights for which these two cartridges are useful at the various ranges are similar. The .25-06 is within 34 pounds of the .240 at 100 yards and 21 pounds at 400 yards.
Recoil is always an important consideration, as anyone can shoot better with a cartridge that kicks less. Remember that bullet placement is the most important factor in killing power. Presumably, one of the main reasons for choosing a .240 or .25-06 over an equally flat shooting .270 or 7mm cartridge for long range hunting of CXP2 game is to minimize recoil. Here are the approximate recoil energy (in ft. lbs.) and recoil velocity (in fps) figures for our comparison loads measured in eight pound hunting rifles.
These recoil figures are surprisingly similar. The .240 kicks very slightly less, but the difference of 0.3 ft. lbs. and 0.2 fps is unlikely to be noticed by most shooters. Functionally, this category is a tie.
Availability of Rifles and Ammunition
To the best of my knowledge, at least among major rifle and ammunition manufacturers, only Weatherby offers rifles (the Mark V) and ammunition in .240 Weatherby Magnum caliber. The .25-06 is not a top seller in rifles or ammunition, but Remington, Hornady, Federal and Winchester all offer factory loaded cartridges in the caliber and .25-06 rifles are available from several manufacturers, including Weatherby (Vanguard and Mark V). The obvious conclusion is that the .25-06 is much more widely distributed than the .240.
If you like the .240 WM cartridge, but for some reason don't like the Weatherby Mark V rifle, you are out of luck. The selection of both production rifles and factory loaded cartridges is much greater in .25-06 caliber.
Summary and Conclusion
The .240 Weatherby Magnum wins this comparison in the velocity, energy, and trajectory categories by significant amounts and is therefore, arguably, the better long range CXP2 game cartridge. It is slightly superior in OGW killing power and kicks a hair less, but these advantages are too small to be decisive.
The .25-06 has a minor advantage in sectional density, but probably not enough to matter in the real world. Its two areas of clear superiority over the .240 are bullet cross-sectional area and the availability of factory built rifles and ammunition.
Copyright 2012 by Chuck Hawks. All rights reserved.