Compared: The .270 Winchester and .308 Winchester
By Chuck Hawks
The .270 Winchester and .308 Winchester are among the best selling rifle cartridges in the world. They are standard, high intensity cartridges, not magnums. Both are all-around hunting cartridges, suitable for a wide variety of CXP2 and CXP3 game and both made our "short list" of all-around cartridges. (See "All-Around Rifle Cartridges," on the Rifle Information page, for details.)
The .270 Winchester
Winchester introduced the famous .270 in 1925. The .270 case was created by simply necking-down a .30-06 case and it is otherwise identical. The same headspace gauges work for both calibers. The .270 was designed to use a 130 grain bullet; later a factory load using a 150 grain bullet was added. The .270 requires a standard (.30-06) length rifle action. For decades after its introduction the .270 was the highest velocity, flattest shooting big game cartridge available from a major manufacturer. A number of gun writers, including Jack O'Connor "the Dean of American Gun Writers," liked the .270 and sang its praises. Almost the entire Guns and Shooting Online staff own and use .270 rifles.
As the years went by .270 rifle and ammunition sales gradually increased and, ultimately, it became a best seller and the standard of comparison among long range big game cartridges. .270 Winchester ammunition is manufactured and used worldwide. The cartridge is available in practically every hunting rifle with an action long enough to accept it, including bolt, lever, pump, autoloading and single shot models. The most popular .270 bullet weights are 130, 140 and 150 grains, all of which it handles with aplomb. The .270 is named for its bore diameter; its groove diameter and bullet diameter is .277".
The .308 Winchester
Winchester developed the .308 (the prototype was called the T65) in conjunction with the U.S. military for reliable function in automatic rifles. The .308 became a NATO standard cartridge, as the 7.62x51mm, in 1954 and replaced the .30-06 in the U.S. In military guise, the .308 delivers identical ballistics to the older cartridge with a 150 grain bullet, the bullet weight for which it was designed. The .308 is undoubtedly the best .30-.32 caliber military cartridge ever developed and it remains in widespread use today in both rifles and machine guns.
However, Winchester introduced the .308 as a hunting cartridge about a year before the military formally adopted the cartridge. The .308 proved to be an exceptionally accurate cartridge and is widely used in target rifles, in addition to its primary role as an all-around big game cartridge. Like the .270, .308 ammunition is manufactured and used worldwide and it is available in a plethora of hunting rifles, including bolt, lever, pump, autoloading and single shot models. Most of the Guns and Shooting Online staff has considerable experience with .308 rifles. The most popular .308 bullet weights are 150, 165 and 180 grains. However, the 180 grain bullet intrudes pretty far into the short cartridge's powder space, reducing its performance compared to the .30-06. The .308 is named for its groove, or bullet, diameter, which is .308". The bore diameter is .300".
The .270 Winchester was designed to use a 130 grain bullet and the .308 Winchester was designed to use a 150 grain bullet, so those are the bullet weights we will compare in this article. These are also probably the best and most common bullet weights for hunting deer and other CXP2 game. This means that the .270 has an automatic advantage in sectional density (SD) and the .308 has an automatic advantage in bullet weight. We shall see how this plays out.
Of course, more than SD and bullet weight enter into any hunting cartridge comparison. We will also compare bullet cross-sectional area, velocity, energy, trajectory, killing power and recoil. The availability of rifles and ammunition is so good in both calibers that for our purposes they can be disregarded.
Most manufacturers of factory loaded ammunition offer .270/130 grain and .308/150 grain loads and maximum reloads are essentially equivalent to factory loads. Remington loads their popular Core-Lokt Pointed Soft Point bullets in factory loads for both calibers and publishes the ballistic coefficients of their bullets. Thus, for uniformity and convenience I chose Remington Express factory loads for comparison. The results with equivalent loads from other brands would be similar.
Sectional density and ballistic coefficient
Sectional density is important because the greater the SD, the longer a bullet is for its weight and, other factors being equal, a long skinny bullet of any given weight penetrates better than a short fat bullet of the same weight. Penetration is an important factor in the length of the wound channel and the amount of tissue disrupted and destroyed.
Although a bullet's shape is not a factor in calculating sectional density, bullets with a higher SD also tend to have a higher ballistic coefficient when of similar form. BC is a measurement of how well a bullet flies through the air. The higher the BC, the more aerodynamic the bullet and the lower its drag.
A higher BC helps a bullet retain more of its initial velocity and energy down range and results in a flatter trajectory. Here are the sectional densities and Remington's published ballistic coefficients for the bullets used in the loads we are comparing.
As you can see, although lighter, the .270/130 grain bullet is superior to the .308/150 grain bullet in both SD and BC. Other things being equal, the .270/130 will shoot flatter and penetrate deeper.
Bullet cross-sectional area
The cross-sectional area of a hunting bullet is important because, other factors being equal, the fatter bullet makes a wider wound channel and damages more tissue. This translates to quicker and more humane kills. Bullet weight has no bearing on frontal area, only caliber. The actual bullet diameter of .270 Winchester bullets is .277"; the diameter of .308 Winchester bullets is .308". Here are the frontal areas of each:
As those numbers reveal, the .308 is superior to the .270 in bullet frontal area. This potential for a wider wound channel is probably the most important reason for the perception that .30 caliber rifles kill better than the smaller calibers, and it constitutes a real advantage for the .308 Winchester.
Higher velocity means flatter trajectory, given bullets of equal ballistic coefficient (BC). Velocity is also an important component in the formula used to compute kinetic energy. Here are the Remington velocity figures from the muzzle (MV) to 400 yards in feet-per-second for our selected .270 Win. and .308 Win. loads, taken in 24" test barrels.
The .270 has about a 240 fps or better advantage in velocity at all ranges. It should come as no surprise that the .270/130, the classic long range hunting load, is faster than the .308/150. The .270/130 will shoot flatter than the .308/150 down range.
Kinetic energy is a measure of the ability to do work. The "work" in this case is penetrating deep into a game animal and powering bullet expansion. The key factors in computing kinetic energy are bullet mass and bullet velocity squared.
Energy is an important factor in bullet performance and killing power. Despite criticisms of energy as a comparative tool by some experts, it is a reasonable indicator of the power of similar rifle cartridges. Here are the Remington energy figures for our selected loads in foot-pounds from the muzzle (ME) to 400 yards.
The 130 grain .270 load shows a small advantage in energy compared to the 150 grain .308 load, ranging from 54 ft. lbs. at the muzzle to 132 ft. lbs. at 400 yards, which is well beyond the MPBR of both cartridges. This difference is unlikely to be noticed when hunting game animals.
Trajectory is important to hunters because the flatter a bullet's trajectory, the easier it is to achieve precise bullet placement at long and unknown ranges. Remember, bullet placement is, by far, the most important factor in achieving clean kills. The primary factors influencing trajectory are bullet velocity and ballistic coefficient.
Ammunition catalogs usually show bullet drop from 100 to 500 yards with a 200 yard zero and that is the way Remington compares our selected loads. Here are the published trajectories for our loads (in inches above or below the line of sight of a scope mounted 1.5" above the bore) out to 400 yards.
The higher velocity and superior BC of the .270 pays dividends in flatter trajectory across the board. At 300 yards, the .270/130 has 1.8" less drop than the .308/150 load. How much this flatter trajectory matters depends on your style of hunting. I would suggest limiting shots to no more than about 250 yards for the .308/150 or 275 yards for the .270/130. When zeroed at 200 yards, the .270 has about a 25 yard range advantage over the .308.
Killing power is the most difficult factor to quantify. Bullet placement is the most important factor in a cartridge's effectiveness on game and that is largely a function of the shooter's skill and judgment, not the cartridge used. The construction and performance of a hunting bullet is also very important and practically every type of hunting bullet is available for either the .270 or the .308. Kinetic energy is one indication of potential killing power, as are bullet frontal area and sectional density, but none of these tells the entire story.
One attempt to estimate killing power that seems to correlate with reality is the Hornady HITS system. Hornady technicians spent considerable time and effort developing this system. Here are the HITS figures at 100 yards for typical .270 Win. 130 grain and .308 Win. 150 grain loads. (For more information about HITS, see the "Expanded Hornady HITS Table" on the Tables, Charts, and Lists page.)
Another way to compare killing power is by using the G&S Online Rifle Cartridge Killing Power Formula developed by yours truly. It include the factors of energy at 100 yards (which incorporates velocity), sectional density (which incorporates bullet weight) and the bullet cross-sectional area of various calibers and loads in a formula that gives a simple number that allows comparisons to be made. You can read more about the Formula and compare dozens of calibers and loads in the articles on the subject included on the Tables, Charts and Lists page. Here are the results for the representative .270/130 and .308/150 loads included in the table.
By either system, there is not enough difference in killing power between the two cartridges at 100 yards to make any practical difference. The .270 advantages in velocity, energy and SD, not great in any case, are largely cancelled out by the .308's advantage in bullet frontal area and bullet weight.
The recoil generated by any rifle/cartridge combination is very important, regardless of the courage, size or strength of the shooter. Virtually everyone can shoot more accurately with a rifle that kicks less. This is true even for experts. The best shooting is done with the rifles that kick the least; look at the results from practically any of the target shooting games for confirmation.
Remember that bullet placement is, by far, the most important ingredient in killing power. No one can consistently put a bullet into the vitals of a game animal with a rifle that causes them to flinch. Here are recoil numbers for .270/130 and .308/150 loads calculated by the Remington Shoot! program for rifles weighing 8 pounds.
In terms of recoil energy, the .308 is the winner by 1.6 ft. lbs. This is not a lot, but it is probably enough to be noticed by most shooters. The .270/130 is above the 15 ft. lbs. limit recommended for consistent accuracy, but below the 20 ft. lb. "do not exceed" level. The .308 is at or slightly below the 15 ft. lb. threshold. Rifles weighing less than 8 pounds (including scope) in both .270 Win. and .308 should be avoided by recoil sensitive shooters.
As this comparison shows, the differences between the .270 and .308 are subtle. Both kill CXP2 game very well with the loads compared in this article. With heavier bullets, both are recommended for hunting CXP3 game. It is the hunter's skill and bullet placement that will matter in the field, not which cartridge is used. For those who are sold on the benefits of short action rifles, the .308 Winchester is the right cartridge. For those who fancy themselves long range marksmen, the .270 Winchester is the natural choice. For everyone else, it is a matter of personal preference.
Copyright 2012 by Chuck Hawks. All rights reserved.