Compared: The .25-06 Remington and 6.5mm Remington Magnum
By Chuck Hawks
The .25-06 Remington and 6.5mm Remington Magnum are based on cases of quite different shape. The .25-06 has a rim diameter of .473" and is simply the .30-06 case necked-down to accept .257" diameter bullets. The cartridge overall length (COL) is 3.250".
The 6.5mm Rem. Mag. is based on the first short magnum case, the .350 Rem. Magnum, necked down to accept .264" diameter bullets. This case has a rim diameter of .532" and the COL is 2.80". It is intended for use in short action rifles. Both cartridges are covered in greater detail on the Rifle Cartridge page.
Although either cartridge can be loaded with light for caliber bullets and used for long range varminting, both are primarily long range, medium game (CXP2) cartridges. The .25-06 is not generally recommended for hunting CXP3 game, such as elk, while the 6.5mm Magnum is more of an all-around cartridge, useful for both deer and elk size animals with appropriate weight bullets. This is one of the main differences between the capabilities of the two cartridges.
The other salient difference is in the availability of rifles and factory loaded ammunition. Most U.S. rifle manufacturers chamber for the .25-06 and all four of the major American ammunition companies load .25-06 cartridges. Conversely, only Remington factory loads 6.5mm Remington Magnum ammunition and only Remington offers rifles in 6.5mm Magnum, and then only on a limited basis.
Anyone with a 6.5mm Rem. Mag. rifle needs to reload to realize the cartridge's full potential. The sole 6.5mm Magnum factory load comes with a 120 grain bullet, but reloading allows the use of any of the popular 140-160 grain .264 bullets that are available from virtually all bullet makers. A 140 grain bullet can be loaded to a MV of 2900-3000 fps in the 6.5mm Rem. Mag. and dramatically expand the capability of the cartridge. This elevates the 6.5mm Mag. into the realm of CXP3 game cartridges. However, for the purposes of this comparison, we are going to stick with factory loads and consider these two cartridges for use only on CXP2 game.
Both cartridges are factory loaded with 120 grain bullets and the SAAMI specified maximum average pressure for both is 53,000 cup. Among the major ammo manufacturers, only Remington offers a 6.5mm Rem. Magnum factory load and it comes with a 120 grain Core-Lokt PSP bullet (BC .323) at a muzzle velocity (MV) of 3210 fps. We will, therefore, use this Remington 120 grain factory load for comparison.
The heaviest bullet normally available for the .25-06 weighs 120 grains and factory loads using this bullet weight are offered by Federal, Remington and Winchester. Remington's version is loaded with a 120 grain Core-Lokt PSP bullet (BC .362) at a MV of 2990 fps. Remington's Core-Lokt bullets are excellent for harvesting CXP2 game animals. For the sake of uniformity, this is the .25-06 load we will use for comparison in this article. We will compare these Remington factory loads in velocity, kinetic energy, trajectory, sectional density (SD), cross-sectional area, killing power and recoil.
Velocity is the most important component of kinetic energy. It also decreases bullet flight time and hence flattens trajectory. Some hunters feel that high velocity per se contributes to killing power by increasing traumatic shock, but that has proven difficult to demonstrate 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 6.5mm Remington Magnum is faster at all ranges with the same weight bullet. This bodes well for its showing in the energy, trajectory and killing power comparisons to come.
Kinetic energy is the measure of 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. Here are the energy figures in foot pounds for our 120 grain Core-Lokt bullets 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 6.5mm Rem. Mag. and .25-06 are capable long range, medium game cartridges. The 6.5mm's higher velocity gives it the advantage in kinetic energy.
The 6.5mm Remington Magnum 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 6.5mm Magnum has a MPBR of 302 yards when zeroed at 257 yards. The .25-06 has a MPBR of 287 yards when zeroed at 244 yards. As these figures reveal, the 6.5mm Rem. Magnum 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 120 grain, .257" and .264" bullets.
The .25/120 grain bullet has a clear advantage in SD compared to the 6.5mm/120 grain bullet. However, both are well above the .225 SD considered excellent for CXP2 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 should be obvious that a .264" diameter bullet has a greater cross-sectional area than a .257" diameter bullet, although the difference is not great. It was a foregone conclusion that the 6.5mm would best the .25-06 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 why we have chosen to compare bullets of the same design (Remington Core-Lokt).
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 100 to 400 yards. (For more on OGW, see the "Expanded Optimum Game Weight Table" on the Tables, Charts, and Lists Page.)
The 6.5mm Magnum has an OGW advantage at all ranges, amounting to 91 pounds at 100 yards and decreasing to only 19 pounds at 400 yards. At ranges over 200 yards, the superior BC of the .257 bullet comes increasingly into play.
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 the .25-06 over a flat shooting 6.5mm or .270 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.
As expected, due primarily to its lower velocity with the same weight bullet, the .25-06 kicks less than the 6.5mm Rem. Mag. Most shooters can do well with rifles producing recoil energy up to about 15 ft. lbs. The 6.5mm Mag. is in this range, while the .25-06 is safely below. The .25-06 is the better cartridge for recoil sensitive shooters.
Summary and Conclusion
The .25-06 has the advantage in sectional density and lower recoil. It is also has a big advantage in the availability of factory built rifles and ammunition.
The 6.5mm Remington Magnum wins this comparison in the velocity, energy, trajectory, cross-sectional area and killing power categories. It is the more effective long range CXP2 game cartridge.
Copyright 2012 by Chuck Hawks. All rights reserved.