Compared: .270 Winchester and 7mm Remington Magnum
By Chuck Hawks
The .270 Winchester and the 7mm Remington Magnum are the best selling, long range, all-around big game hunting cartridges in the world. The 7mm Magnum is obviously somewhat more powerful than the standard .270 Winchester, but which cartridge makes the most sense? Hopefully, this comparison will help Guns and Shooting Online readers answer this question for themselves.
The .270 Winchester
The .270 was introduced by Winchester in 1925 for their then new Model 54 bolt action rifle. It was based on a .30-06 case that was simply necked down to accept a .277" diameter, 130 grain bullet. (.270" is the bore diameter, the traditional way to name rifle cartridges.) The .270 makes optimum use of the .30-06 case's powder capacity and it became the standard of comparison among long range big game cartridges. The .270 was subsequently offered with bullets ranging in weight from about 100-160 grains and it became a favorite all-around hunting cartridge, widely used wherever big game in hunted.
Almost every hunting rifle with a standard length action is offered in .270 Winchester. The basic cartridge dimensions include a .473" rim diameter, .470" head diameter, .441" shoulder diameter, 17.5-degree shoulder angle, 2.540" case length and 3.340" maximum cartridge overall length.
A wide range of bullet weights are offered in .270 caliber and virtually all ammunition manufacturers offer .270 Win. factory loads. For example, Remington currently offers 10 different .270 loads using bullets weighing from 115-150 grains. However, bullets weighing 130, 140 and 150 grains are the most popular for use in the .270.
Many .270 fans, including the late Jack O'Connor, consider the original 130 grain bullet the best choice and Remington offers their sleek AccuTip boat-tail bullet at a MV of 3060 fps in this weight. This is the load we will use for this comparison.
The 7mm Remington Magnum
Remington introduced their 7mm Magnum cartridge in 1962, based on a necked-down .338 Win. Mag. case. This is, itself, a shortened (.30-06 length) and blown out version of the .300 H&H Belted Magnum case, with a standard .532" magnum rim diameter and a sharp 25 degree shoulder. Maximum cartridge overall length is specified as 3.29". Previous 7mm Magnums, among them the Weatherby and 7x61mm Sharpe & Hart versions, are similar in concept and performance, but it is the 7mm Rem. Mag. that caught the shooting public's fancy.
The 7mm Remington Magnum has proven excellent for use on Class 2 and Class 3 game, particularly at long range. The popular saying that the 7mm Mags shoot as flat as a .270 and hit as hard as a .30-06 is not far off the mark. In rifles of typical magnum weight (about 8.5 pounds), the 7mm Magnum kicks about as hard as a .30-06, which means that it is within the reach of most experienced shooters. It is, however, not a cartridge for the inexperienced shooter.
All major ammunition companies load the 7mm Rem. Mag. cartridge. Most magnum rifle models are available in 7mm Rem. Mag., and both factory loaded ammunition and rifles to shoot it are available just about everywhere big game is legally hunted.
Remington currently offers 10 factory loads for their 7mm Magnum, loaded with bullets weighing 140, 150 and 160 grains. 150 grains seem to be about the optimum all-around bullet weight for any 7mm Magnum rifle, so that is the bullet weight that we will use for this comparison. Remington offers a 7mm Rem. Mag. load using their 150 grain AccuTip boat-tail bullet at a MV of 3110 fps and that is the specific load that we will use to represent the 7mm Magnum in this comparison.
We will compare our selected .270 Win. and 7mm Rem. Mag. factory loads in bullet sectional density (SD) and ballistic coefficient (BC), cross-sectional area, velocity, energy, trajectory, killing power and recoil. Both the .270 Winchester and 7mm Rem. Magnum are offered in an exceptionally wide variety of factory loaded ammunition and rifles, so availability is not a consideration with these two calibers.
Sectional Density and Ballistic Coefficient
Sectional density is defined as a bullet's weight (in pounds) divided by the square of its diameter (in inches). 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, the amount of tissue disrupted and destroyed and thus killing power.
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 air 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 ballistic coefficients for the bullets used in the loads compared in this article.
The 7mm/150 has the advantage in both SD and BC with these bullets of identical form. SD is not a direct factor in calculating BC, but when two bullets are of basically identical form, the bullet with the higher SD usually also has a superior BC. Given bullets of identical construction, other factors being equal, the 150 grain 7mm bullet should penetrate deeper than the 130 grain .270 bullet and also offer the advantage of a flatter trajectory if launched at the same velocity.
Bullet weight has no bearing on frontal area, only caliber. 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. The actual bullet diameter of 7mm Magnum bullets is .284" and the bullet diameter of .270 bullets is .277". Following are the cross-sectional areas of each in square inches.
As those numbers reveal, the 7mm has a slight advantage over the .270 in bullet frontal area. However, this small difference is unlikely to impress any big game animal.
Higher velocity means flatter trajectory, given bullets of equal ballistic coefficient (BC). Velocity is also the most 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 7mm Rem. Mag. loads, measured in 24" test barrels.
The 7mm Rem. Mag. has a minor 50 fps advantage in velocity at the muzzle, increasing to 137 fps at 300 yards (about the MPBR of either cartridge). We will soon see how much this effects trajectory.
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. It is a good 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.
These figures show that both calibers are capable for hunting Class 2 and Class 3 class game to beyond 400 yards. However, the 7mm Rem. Mag. has a clear advantage over the .270 in kinetic energy at all ranges. The difference is 515 ft. lbs. at 100 yards and 494 ft. lbs. at 300 yards. You could summarize the situation by saying that the 7mm Mag. offers about 500 ft. lbs. more energy at typical hunting ranges.
Trajectory is important to hunters, because the flatter a bullet's trajectory, the easier it is to achieve accurate bullet placement at unknown ranges and bullet placement is, by far, the most important factor in killing power. The primary factors influencing trajectory are velocity and ballistic coefficient.
Remington ballistic tables show bullet drop for our selected loads based on a 200 yard zero. Here are the published trajectories (in inches above or below the line of sight of a scope mounted 1.5" above the bore) out to 400 yards.
Our 7mm Mag. bullet shoots very slightly flatter than our .270 bullet. However, the tiny difference in trajectory is not significant. It would be hard to conceive of a real world hunting situation where a ½ inch difference in drop at 300 yards would matter.
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. 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 Win. or 7mm Rem. Mag. 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 include at least some of the relevant factors is the Optimum Game Weight (OGW) formula developed by Edward A. Matunas and published in the Lyman 47th Reloading Manual. To reduce the variables, Matunas started with the assumption that bullet design and placement are adequate for the task at hand. OGW is an attempt to quantify the live animal weight and maximum distance for which a hunting load is optimum. Thus it compares the killing power of different cartridges and loads in a way that is relevant in the field.
Here are the OGW ranges from the "Expanded Optimum Game Weight Table" on the Tables, Charts, and Lists index page for the 150 grain 7mm Rem. Mag. and 130 grain .270 factory loads for 200 pound, 400 pound and 600 pound animals at any distance out to 400 yards. (Distances beyond 400 yards, which is well beyond the MPBR of either cartridge, are merely noted as "400+ yards.")
Both of these calibers are capable of harvesting Class 2 and Class 3 animals, but our 7mm Rem. Mag. load is superior for large animals, such as elk, when the range stretches beyond 100 yards.
This is the category that magnum fans generally like to ignore, but it is actually of crucial importance. Bullet placement is, by far, the most important factor in killing power and rifle recoil is the enemy of accurate bullet placement. A hunter who flinches in anticipation of the rifle firing will wound a lot of game. Severe flinches result in those embarrassing "grounders" you sometimes see at the range. Anyone can shoot more accurately with a rifle that kicks less. That fact has been demonstrated countless times. Here are some recoil energy (in foot pounds) and recoil velocity (in feet-per-second) figures for our 7mm Rem. Mag. and .270 Win. loads fired in 8.5 pound rifles.
If you accept the common generalization that the average shooter cannot long tolerate recoil above about 20 ft. lbs. without developing a flinch, and you should, then the 7mm Rem. Mag. barely squeezes under the permissible recoil limit, while the .270 is clearly more pleasant to shoot. The difference in recoil is significant and favors the .270.
Rifle weight is directly proportional to recoil. Reduce the weight of a .270 rifle from 8.5 to 7.5 pounds (a fairly typical weight for a .270 sporter) and the recoil increases to about 16.1 ft. lbs. and 11.8 fps, which is still noticeably less than the 7mm Magnum's kick in a rifle weighing a full pound more. In a ultra-lightweight 6.5 pound rifle, the .270's recoil becomes comparable to the 7mm Rem. Mag. (18.6 ft. lbs. and 13.4 fps) The lesson here is that a 7mm Mag. rifle needs to weigh about two pounds more than a .270 rifle to keep the recoil at similar levels. For a mountain rifle or lightweight stalking rifle, the .270 is clearly the superior cartridge.
Summary and Conclusion
The 150 grain 7mm Remington Magnum load is noticeably superior to the 130 grain .270 Winchester load in terms of bullet SD and BC, energy and OGW killing power. The .270 clearly wins in the area of lower recoil. In velocity, trajectory and cross-sectional area the 7mm Mag. superiority is inconsequential.
For most hunting purposes, there is actually not a lot of practical difference in capability between these two big game cartridges. Nor is there a definitive difference in the availability of rifles, ammunition and bullets for reloading. Both are popular calibers, among the top 10 in sales, and well proven on all sorts of big game around the world.
The 7mm Remington Magnum is superior to the .270 Winchester for use on the largest Class 3 game, such as Roosevelt elk and Alaskan moose. Both are excellent long range big game calibers and a good choice for mixed bag hunts that include animals such as North American mule deer and Rocky Mountain elk. The .270 would be a more appropriate choice for hunting most Class 2 game, such as pronghorn antelope and the various species of North American deer. Both the 7mm Remington Magnum and .270 Winchester made the short list of four top all-around calibers, along with the .30-06 Springfield and .308 Winchester. (See "All Around Rifle Cartridges" on the Rifle Information page for details.)
Copyright 2013 by Chuck Hawks. All rights reserved.