Compared: The .357 Magnum and 10mm Auto
By Chuck Hawks
These two cartridges are outstanding for self-defense and also adequate for hunting the smaller species of CXP2 game. They are sometimes chosen for protection against both two and four-legged predators in the field. Typical bullet weights for the .357 Magnum range from about 110 grains to 200 grains and for the 10mm Auto from 135 to 200 grains. The .357 Mag. is chambered in a wide variety of revolvers, while the 10mm Auto is available today primarily in the full size Glock Model 20 and the sub-compact Glock Model 29 autoloading pistols.
Introduced by Smith & Wesson in 1935, the .357 Magnum was the original magnum revolver cartridge. It was based on a lengthened and strengthened .38 Special case loaded to higher pressure. For this reason, any .357 Magnum revolver can also safely fire all .38 Special and .38 Special +P ammunition. The .357 is one of the all-time best selling handgun cartridges, widely used for both hunting and personal defense. It has also been adapted to rifles.
The .357 Magnum has become the standard of comparison among personal defense handgun cartridges, with the highest percentage of one shot stops of any handgun cartridge. Almost every revolver that can stand the pressure is chambered for the .357 Magnum and there is an equally large selection of factory loaded .357 Magnum ammunition. Virtually all ammunition manufacturers load .357 Magnum cartridges. There are small frame, medium frame and large frame .357 revolvers. It is also one of the most popular calibers in single shot pistols and even some autoloading pistols have been adapted to the cartridge, making for an extensive choice of guns in the caliber.
The .357 Magnum's cartridge dimensions are as follows: rim diameter = .440", head diameter = 0.379", mouth OD = 0.379", case length = 1.290", bullet diameter = 0.357", cartridge overall length = 1.590", Maximum average pressure (MAP) = 35,000 psi.
For most of its life, the standard .357 Magnum factory load has driven a 158 grain bullet of .357" diameter at a muzzle velocity (MV) of 1550 fps from an 8-3/8" barrel (Remington figures). Because the .357 was loaded to full pressure, this velocity figure was pretty close and was verified by independent chronograph tests, including mine. In this the age of the tort lawyer, the SAAMI maximum average pressure (MAP) of the .357 Magnum has been reduced to 35,000 psi. The factory loaded 158 grain bullet now has a catalog MV of approximately 1250 fps and muzzle energy (ME) of 548 ft. lbs.
.357 Magnum reloaders have a huge choice of suitable bullets and powders. According to the Hornady reloading manual, reloaders can drive 158 grain bullets at up to 1400 fps and 180 grain bullets at 1150 fps within current SAAMI pressure limits. For the reloader, the availability of cases is important and in this area the .357 Magnum has a big advantage over the 10mm Auto.
The 10mm Auto was introduced in 1983 by Norma for the flawed Bren 10 pistol. The original Norma loads launched a 200 grain FMJ bullet at 1200 fps and a 170 grain JHP bullet at 1340 fps. These were full power loads. The case was developed from a drastically shortened .30 Remington rifle cartridge case. While the Bren 10 pistol was a flop, the cartridge was picked-up by Colt for the Delta Elite 1911, Smith & Wesson for the Model 1006 and Glock in their Models 20 and 29. (Plus a compensated version of the G20.) The G20 became the most enduring and successful of the 10mm pistols and is a favorite of the Guns and Shooting Online staff.
The 10mm Auto is arguably the best of the standard autoloading pistol cartridges for the outdoorsman and just about the only one suitable for handgun hunting of CXP2 (deer size) game. Glock, for example, markets their G20 pistol primarily to hunters and outdoorsmen. Unlike most auto pistol cartridges, the 10mm can handle bullets of reasonable sectional density (SD) at decent velocities.
The 10mm Auto's cartridge dimensions are as follows: rim and head diameter = 0.425", mouth OD = 0.423", case length = 0.992", bullet diameter = 0.400", cartridge overall length = 1.260", Maximum average pressure (MAP) = 37,500 psi. The 10mm is probably most useful with the caliber's heavier bullet weights, usually 175-200 grains.
The Winchester Super-X 175 grain Silvertip offering, the most common of full power factory loads, achieves a MV of 1290 fps from a 5.5" test barrel. More common in factory loaded form is the reduced power "FBI Lite" 10mm load, which duplicates the performance of .40 S&W cartridges (180 grain bullet at about 1000 fps). Reloaders can do better than most factory loads. According to the Hornady reloading manual, reloaders can drive 155 grain bullets up to 1450 fps, 180 grain bullets at 1250 fps and 200 grain bullets at 1150 fps within SAAMI pressure limits.
10mm Auto ammunition is factory loaded by Federal, Hornady, Norma, PMC, Remington, Winchester, Cor-Bon and some of the lesser known ammo companies. Most 10mm factory loads are loaded to reduced velocity. For example, the popular 180 grain bullet weight is loaded about 100 fps slower than maximum reloads.
We will use Hornady Custom factory loads in each caliber for this comparison. These are not maximum performance loads for either caliber, being well below the top loads shown in the Hornady Handbook of Cartridge Reloading. However, they are typical of both 10mm Auto and .357 Mag. factory loads from the major U.S. manufacturers.
To represent the .357 Magnum, we will use the 158 grain XTP-JHP factory load. To represent the 10mm Auto, we will use the 180 grain XTP-JHP factory load. We will compare these factory loads in velocity, energy, trajectory, sectional density, bullet diameter and recoil.
Velocity is important for initiating bullet expansion and it is the most important factor in calculating kinetic energy. Higher velocity flattens trajectory, making hitting easier at extended ranges and particularly at unknown ranges in the field. Here are the velocities in feet per second (fps) of our comparison loads at the muzzle, 50 yards and 100 yards.
The .357 Mag. shows a clear velocity advantage at all distances over the 10mm Auto. The .357 wins the velocity comparison.
Kinetic energy is defined as the ability to do work. In this case, the "work" involved is primarily powering bullet penetration and expansion. Both are, of course, necessary for lethality. It is also worth noting that kinetic energy is also reasonably good indicator of potential killing power. Here are the energy figures in foot-pounds (ft. lbs.) for our comparison loads at the muzzle (ME), 50 yards and 100 yards.
These are both very potent cartridges for personal protection and they are adequate for hunting the smaller species of CXP2 game at short range. However, the .357 has a worthwhile advantage in kinetic energy at the muzzle and 50 yards. At 100 yards, the heavier 10mm bullet has almost caught up with the 158 grain .357 in energy.
Velocity and ballistic coefficient are the factors that primarily determine a bullet's trajectory. Sometimes the need for personal defense occurs at greater distances than anticipated. Seven yards or less may be the statistical average, but sometimes bad guys do not play by the rules and bring slug shooting shotguns, rifles or magnum revolvers to gunfights. In such circumstances, the need to reach out and touch someone makes a flat trajectory important. The flatter the trajectory, the easier it is to hit the target as the range increases. This particularly applies to those who carry a handgun for protection in the field against two-legged predators when camping, fishing or hiking. Trajectory is even more important for a hunting handgun, since wild game is unlikely to be encountered at seven yards or less.
For purposes of comparison, we will assume the common 25 yard zero distance. Here are the approximate trajectories for our comparison loads from 25 yards to 100 yards.
There is not much difference in trajectory with a 25 yard zero. The slight trajectory advantage of the .357 Mag. is due to its bullet's superior ballistic coefficient.
It is worth noting that for handgun hunting or protection in the field, either of these loads can be zeroed at 100 yards without danger of over shooting the target at intermediate distances. This dramatically extends the maximum point blank range (+/- 3.2") to well beyond 100 yards.
Sectional Density is the ratio of a bullet's weight (in pounds) to its diameter squared (in inches). SD is important when comparing cartridges and loads because, other factors (such as impact velocity and bullet expansion) being equal, the bullet with the greatest SD will penetrate deeper, creating a longer wound cavity and increasing tissue destruction. Obviously, however, if the bullet penetrates all the way through the target, wounding ceases. Superior SD also improves the penetration of barrier materials, giving the bullet a better chance to reach a target on the other side (other factors being equal).
The .357/158 has a clear advantage in SD over the 10mm/180. This means that the .357 should provide superior penetration.
Bullet diameter determines cross-sectional area. Given an equal percentage of bullet expansion, a larger diameter bullet will create a wider wound cavity, destroying more tissue. Bullet diameter and SD tend to cancel each other, superior diameter creating a wider bullet track and superior SD a longer bullet track, other factors being equal. Here are the actual bullet diameters of our two cartridges.
The 10mm has a clear advantage over the .357 in bullet diameter and should produce a wider wound channel.
The most popular 10mm service pistol is the Glock 20. it is hard to say what is the most popular, full size .357 revolver, but the Ruger Blackhawk with a 6.5" barrel must be right up there. The G20 weighs approximately 2.44 pounds with a loaded magazine and the Blackhawk weighs 3.0 pounds. These are the gun weights we will use when calculating the recoil of our comparison loads. We will also calculate recoil for the .357 in a 2.44 pound pistol, to compare the kick in guns of identical weight.
Recoil is a bad thing, as it distracts the shooter, leads to flinching and degrades accuracy. Anyone can shoot better with a pistol that kicks less.
Both of these cartridges are known for rather stiff recoil. The 10mm/180 comes back harder in guns of typical weight, because it is chambered in a lighter pistol. However, in guns of equal weight, the .357 kicks slightly harder than the 10mm.
Summary and Conclusion
The .357 Magnum beats the 10mm Auto in every performance category except bullet diameter. However, in most cases the two loads are not dramatically different.
The .357 Magnum is more versatile, because it can handle a wider range of bullet weights and loads, including all .38 Special ammunition. 357 Magnum guns and ammunition are much more popular and widely distributed than 10mm guns and ammo and this means a substantially greater availability of pistols and lower cost .357 ammunition, a significant advantage.
Copyright 2012 by Chuck Hawks. All rights reserved.