Compared: the .308 Cartridge Family (.243 Win., .260 Rem., 7mm-08 Rem., .308 Win., .338 Federal and .358 Win.)
By Chuck Hawks
This article will examine the entire .308 family of cartridges as typically factory loaded to SAAMI specifications. The .308 Winchester set the standard for short action rifle cartridges and it is the most successful such design ever created. It was designed by Winchester at the request of the US Army to fire a 150 grain bullet at the same muzzle velocity (MV) as the then standard .30-06 service round.
Due to the great popularity of short action, magazine rifles designed to handle ".308 length" cartridges, the .308 parent case has been necked up and down (usually without other changes) and standardized by the major ammunition manufacturers to accommodate bullets ranging from .243" to .358". The first cartridge in the family, the .308 Winchester, was introduced in 1952 and the most recent, the .338 Federal, was introduced in 2006. That time span, in itself, is testimony to the astonishing versatility and popularity of the parent case.
The basic .308 case has proven to be so versatile that it is fair to say, given appropriate caliber and load selection, that this family of cartridges can properly be used to hunt all North American Game from varmints to moose and all CXP2 and CXP3 game worldwide at reasonable ranges. There are many other fine cartridges, but unless dangerous or outsize game is on the menu, there is really no necessity for the 21st Century hunter to look beyond the .308 family. (For additional details about the various cartridges included in this comparison, see the Rifle Cartridge Page. -Ed.)
In order to keep this comparison to a manageable size, one standard factory load was selected to represent each caliber. All of these loads use spitzer (pointed) bullets and were chosen to keep this comparison as fair as possible. The representative loads chosen to represent each caliber are:
We will compare these six cartridges and loads in sectional density (SD), bullet-cross-sectional area, velocity, kinetic energy, trajectory, killing power and recoil. At the end, we will conclude with a few pertinent comments and observations.
The sectional density (SD) of bullets is calculated by dividing a bullet's weight (in pounds) by the square of its diameter (in inches). Note that the shape, material or ballistic coefficient of the bullet has no bearing on SD, only weight and diameter count. If you compare bullets of the same weight in different calibers, the smaller caliber will have superior SD for any given weight.
Sectional density is important because, given bullets of identical design at identical velocity, the bullet with the greatest SD will penetrate the deepest. A simple example is that a long and slender shape like a needle penetrates better than a blunt shape such as a round ball of the same weight at the same velocity. The deeper the wound channel (of any given diameter) in a game animal the more tissue is destroyed and the greater the killing power. Here are the SD numbers for our selected bullet weights:
SD's above about .200 are considered appropriate for CXP2 class game (deer, antelope, goats, sheep and black bear). Our chosen bullets in all calibers thus easily qualify for hunting CXP2 game.
The real standout in SD among our calibers is the .260 Remington. This illustrates why 6.5mm cartridges have earned such an outstanding reputation in game fields around the world for deep penetration.
Bullet cross-sectional (frontal) area is important because the wider the wound cavity (of any given depth), the more tissue is destroyed and the greater the killing power. Bullet cross-sectional area is independent of bullet weight. The actual bullet diameters of our various calibers are .243", .264", .284", .308", .338" and .358". Here are the bullet cross-sectional areas for our calibers:
The .358 bullet will, given the same percentage of bullet expansion, always punch a larger diameter hole than any of the smaller calibers. The advantage in cross-sectional area, not surprisingly, belongs to the two medium bores, the .338 Federal and .358 Winchester, with our four small bore calibers trailing behind.
In terms of the volume of a wound cavity, sectional density and cross-sectional area tend to balance out. Other things being equal, a load that scores well in both categories, such as the .338 Federal, can be expected to create a devastating (wide and deep) wound.
Above some certain impact velocity there may or may not be a "shock" effect on an animal's system (that theory is widely debated), but for sure higher velocity flattens trajectory. Velocity is also a major factor in computing kinetic energy. Here are the claimed velocity figures (in feet per second) at the muzzle, 100, 200, and 300 yards for our selected factory loads:
The velocity champion of the family is the .243 Win. The .243 starts fastest and ends fastest, but its 300 fps advantage over the .338 Federal at the muzzle has shrunk to 155 fps at 300 yards. That is not inconsequential, but it is less than most of us might have thought. Except for the .358 Winchester, all the rest of our cartridges show surprisingly similar velocities at 300 yards. We will see how the differences in velocity affect trajectory shortly.
Energy delivered on target, bullet diameter and bullet penetration are the keys to killing power. The bullet's remaining energy at impact powers penetration and expansion. Kinetic energy is essentially a function of mass and the square of velocity and is expressed in foot-pounds.
In this important category the relatively heavy bullet and good velocity of the .338 Federal pays dividends. The .338 yields higher energy at all ranges than any of the other members of the family. The surprise of the clan is probably the 7mm-08, which with our selected load has surpassed all of the other cartridges by 100 yards and maintains its edge in kinetic energy all the way to 300 yards and beyond.
Trajectory is important because a bullet that shoots flatter is easier to place accurately as the range increases and bullet placement is, by far, the most important factor in killing power. The following trajectory figures are predicated on scoped rifles with the line of sight 1.5" above the center of the bore. For comparison purposes, each load is zeroed dead on at 200 yards.
The .243 Winchester, due primarily to its higher velocity, has the flattest trajectory across the board. Notice, however, that the second place 7mm-08 stays within +/- 0.3" throughout, an excellent performance with a 40 grain heavier bullet fired from the same size case.
Optimum Game Weight (OGW) is a system devised by Edward A. Matunas to express the killing power of rifle cartridges in terms of distance and the weight of the animal. We need not go into the formula itself here, suffice to say that while not perfect, the OGW system does seem to have a higher correlation with reality than most other systems for estimating killing power. The figures below represent animal weight in pounds and distance in yards.
The .338 Federal has the advantage in theoretical killing power over all of the other .308 based cartridges and out to 200 yards the .358 Winchester stays in second place. Medium bore cartridges are designed for killing large animals. They are not represented here, but bullets weighing 220 to 250 grains are popular with reloaders who use their .358 rifles on large game. For similar purposes, bullets in the 210-225 grain range find favor among .338 Federal handloaders.
Among the small bore cartridges, the flat shooting .243 Winchester trails the pack at all ranges. The .308 Winchester has the edge at short range with our representative 150 grain factory load and it should be noted that by switching to a 180 grain bullet the .308 shooter can increase the OGW of the cartridge by about 100 pounds at all ranges. By the time the bullets reach 200 yards our selected loads for the .260, 7mm-08 and .308 are quite similar in OGW killing power.
Recoil or "kick" is far more important than usually realized. Everyone shoots better with a gun that kicks less. That has been proven repeatedly and bullet placement is the most important factor in achieving a quick, humane kill. Get almost any reasonably appropriate bullet into the vitals and you are in business. A solid hit in the heart/lung area of a Roosevelt elk with a 140 grain .260 bullet is far preferable to putting a 270 grain .375 Magnum bullet too far back. Power will not make up for incorrect bullet placement and flinching due to anticipating the recoil and muzzle blast is the single biggest cause of bad bullet placement. Here are the approximate recoil energy (in foot-pounds) and velocity (in feet-per-second) figures for our representative loads fired in an 8 pound rifle:
There is a big difference in recoil between these calibers. The flat shooting .243 can be enjoyed by almost all shooters and its low recoil allows hunters to take advantage of the very high level of accuracy delivered by most .243 rifles. The result is precise bullet placement. This is the foundation of the .243's reputation as a fine deer and general CXP2 game slayer.
Among our middle tier of calibers, the .260 kicks noticeably less than the 7mm-08, which in turn kicks noticeably less than the .308. All are within the maximum of 15 ft. lbs. of recoil energy with which it is generalized that most shooters can do good work. Balance the factors discussed above against the kick to choose between them.
Remember that these recoil figures are quoted in an eight pound (medium weight) rifle. Reduce the rifle weight to 6.5 or 7 pounds and the recoil figures (energy and, especially, velocity) increase dramatically. The .308 Winchester can go over 20 ft. lbs. of recoil energy and the .338 Federal and .358 Winchester are decidedly unpleasant to shoot with full power loads in an ultra-light rifle. (As the owner of a Kimber 84M rifle in .338 Federal, I know of what I speak!)
Reloaders have a definite advantage in this area. A 200 grain bullet at a MV of approximately 2400 fps will still kill decisively out to 200 yards, yet substantially reduces the recoil of a .338 or .358.
It is hard to go wrong with any of the .308 family of cartridges if they are used appropriately. For a combination varmint, small predator and CXP2 game rifle, the .243 Winchester is the obvious choice. Ditto for anyone seeking light recoil and/or extreme accuracy.
For general purpose CXP2 game hunting it is very hard to beat either the .260 Remington or 7mm-08 Remington. The .308 Winchester remains the best choice for mixed bag (CXP2 and CXP3) big game hunts because it is commonly factory loaded with bullets weighing not only 150 grains, but also 165 and 180 grains. These heavier bullet choices give the .308 an advantage on large game.
For the Roosevelt elk hunter in the dense woods of the Pacific Northwest the .358 Winchester is an excellent choice, while the elk hunter in more open country would probably favor the .338 Federal. These two are the smallest, high intensity, medium bore cartridges on the market today; the biggest punch available in a small package.
Copyright 2008, 2012 by Chuck Hawks. All rights reserved.