Compared: The .40 S&W and 10mm Auto
By Chuck Hawks
These two cartridges are related, since the .40 is based on a shortened 10mm case designed to work in 9x19mm length magazines and 9x19mm size pistols. Both cartridges use the same .400" diameter bullets and are very effective against two-legged predators, but due to its smaller case, the .40 S&W ("Small and Weak") cannot match the ballistics or versatility of the 10mm Auto, which can also be effective on four-legged predators. Available bullet weights range from about 135 grains to 200 grains.
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 accuracy of most 10mm Auto pistols is good, better than most .40 S&W pistols. Why this should be, I don't know. Another oddity is that the G20 10mm Auto pistol can also feed and reliably shoot .40 S&W factory loads. Both cartridges headspace on the case mouth and are different in COL, therefore they are not interchangeable. However, the Glock's extractor will hold the shorter .40 S&W cartridge against the breech face so that it can be fired by the striker. Surprisingly, we found both accuracy and reliability to be good!
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.
.40 Smith & Wesson
The .40 S&W cartridge, which was actually designed by Winchester, was introduced in 1990. The FBI had adopted the 10mm Auto cartridge, only to find than too many FBI agents could not handle the recoil in the S&W pistol the Agency had chosen for their new service autoloader. Also, the pistol's grip size was uncomfortably large for agents with small hands, especially female agents. Consequently, the FBI's Firearms Training Unit developed a reduced power 10mm Auto load called the "10mm Lite." This used a 180 grain bullet at a MV of 980 fps and met the FBI's requirements for bullet expansion and penetration.
The light load did not need the big 10mm case to hold its reduced powder charge, so Winchester developed the shorter .40 S&W at that company's request. The shorter cartridge could then be chambered in smaller, 9mm size pistols, an advantage for shooters with small hands and for concealed carry. Here are the .40's dimensions: rim and head diameter = 0.424", mouth OD = 0.423", case length = 0.850", bullet diameter = 0.400", cartridge overall length = 1.260", MAP = 35,000 psi.
An interesting sidelight is that the smaller .40 S&W case requires a MAP around 32,000 psi to launch a 180 grain bullet at 980 fps, while the 10mm Auto achieves the same MV with the same bullet at a MAP around 25,000 psi. This is because the more confined volume of the .40 case builds pressure faster. The 10mm Lite's lower MAP is easier on the gun.
Due to its limited case capacity, bullets in the 135-165 grain range are probably most suitable in the .40 S&W for civilian self-defense, although factory loads are commonly offered with bullets up to 180 grains and that bullet weight remains popular with the FBI, police and many civilian .40 S&W shooters. Typical 155 grain factory loads achieve a MV around 1180 fps from a 4" test barrel, while typical 180 grain factory loads achieve MV's around 980 fps. According to the Hornady reloading manual, with maximum loads, the .40 S&W can achieve MV's of 1300 fps with 155 grain bullets and 1100 fps with 180 grain bullets.
Following the .40's adoption by the FBI, many U.S. police departments and civilians followed suit and today the .40 S&W is among our most popular handgun cartridges. Both ammunition and pistols are very widely distributed and commonly discounted. This widespread availability is the .40's greatest advantage over the 10mm Auto.
We will use Hornady Custom factory loads in each caliber for this comparison. These are not maximum performance loads for either caliber, being a couple of steps below the top loads shown in the Hornady Handbook of Cartridge Reloading. However, they are typical of both .40 S&W and 10mm Auto factory loads from the major U.S. manufacturers.
Bear in mind that the 10mm is also available in 10mm Lite form that duplicates the ballistics of the 180 grain .40 S&W load. For that reason, there is no point in including it in this comparison.
To represent the .40 S&W, we will use the 155 grain XTP-JHP factory load and the 180 grain XTP-JHP factory load. To represent the 10mm Auto we will use the 180 grain XTP-JHP factory load. All bullets measure .400" in diameter and, therefore, are identical in cross-sectional area. We will compare these factory loads in velocity, energy, trajectory, sectional density 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.
· .40 S&W, 155 grain XTP: 1180 fps MV, 1061 fps at 50 yards, 980 fps at 100 yards
· .40 S&W, 180 grain XTP: 950 fps MV, 903 fps at 50 yards, 862 fps at 100 yards
· 10mm, 180 grain XTP: 1180 fps MV, 1077 fps at 50 yards, 1004 fps at 100 yards
The velocities of the 155 grain .40 and 180 grain 10mm are quite similar. With bullets of the same weight, 180 grains in this case, the 10mm shows a clear velocity advantage at all distances. The 10mm wins the velocity comparison, which bodes well for its performance in the energy comparison to come.
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 a reasonably good indicator of killing power in similar calibers shooting similar bullets. Here are the energy figures in foot-pounds (ft. lbs.) for our comparison loads at the muzzle (ME), 50 yards and 100 yards.
· .40 S&W, 155 grain XTP: 479 ft. lbs. ME, 388 ft. lbs. at 50 yards, 331 ft. lbs. at 100 yards
· .40 S&W, 180 grain XTP: 361 ft. lbs. ME, 326 ft. lbs. at 50 yards, 297 ft. lbs. at 100 yards
· 10mm, 180 grain XTP: 556 ft. lbs. ME, 464 ft. lbs. at 50 yards, 403 ft. lbs. at 100 yards
As you can see, the 180 grain 10mm load considerably out performs both .40 loads in kinetic energy at all ranges. This additional energy contributes substantially to the 10's greater killing power and is what qualifies it for close range use on the smaller species of CXP2 game. It is also, of course, a very potent cartridge for personal protection.
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 three loads from 25 yards to 100 yards.
· .40 S&W, 155 grain XTP (BC .137) at 1180 fps: +/- 0 at 25 yards, -0.9" at 50 yards, -3.7" at 75 yards, -8.5" at 100 yards
· .40 S&W, 180 grain XTP (BC .164) at 950 fps: +/- 0 at 25 yards, -1.7" at 50 yards, -6.1" at 75 yards, -13.3" at 100 yards
· 10mm, 180 grain XTP (BC .164) at 1180 fps: +/- 0 at 25 yards, -0.8" at 50 yards, -3.5" at 75 yards, -8.0" at 100 yards
Because our 10mm/180 grain and .40/155 grain loads have the same muzzle velocity, there is not much difference in trajectory with a 25 yard zero. The slight trajectory advantage of the 10mm Auto load is due to its heavier bullet's superior ballistic coefficient; a heavier for caliber bullet of similar form retains velocity better, due to lower drag, and thus shoots flatter. The slower .40/180 grain load suffers in this comparison and is clearly inferior.
It is worth noting that for handgun hunting or protection in the field, the 10mm/180 load can be zeroed at 100 yards without danger of over shooting the target at intermediate distances. This extends its maximum point blank range (+/- 3.2") to 118 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 actual bullet diameter for both of these calibers is the same: .400". Here are the SD's for our selected bullets.
· .400", 155 grain XTP: .138
· .400", 180 grain XTP: .161
This is a substantial difference in SD, with the advantage in penetration being in favor of the 180 grain bullet, given equal velocity.
The most popular service pistols for both of these cartridges are manufactured by Glock, the G20 in the case of the 10mm and the G22 in the case of the .40 S&W. The medium frame G22 weighs approximately 2.13 pounds with a loaded magazine, while the large frame G20 weighs approximately 2.44 pounds with a loaded magazine. These are the gun weights we will use when calculating the recoil of our comparison loads. 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.
· .40 S&W, 155 grain XTP at 1180 fps, 2.13 lb. pistol: 7.45 ft. lbs energy, 15.0 fps velocity
· .40 S&W, 180 grain XTP at 950 fps, 2.13 lb. pistol: 5.96 ft. lbs energy, 13.4 fps velocity
· 10mm, 180 grain XTP at 1180 fps, 2.44 lb. pistol: 8.33 ft. lbs. energy, 14.8 fps velocity
Both of these cartridges are known for rather sharp recoil, although the polymer frame of full size Glock pistols, plus their double-stack-wide, comfortably angled grips, helps to minimize the subjective effect of recoil. The 10mm/180 comes back with more free recoil energy, while the .40/155 S&W drives its somewhat lighter pistol rearward slightly faster. The recoil felt by the shooter is a combination of both factors. The lower velocity .40/180 load generates the least recoil of our comparison loads, which figures since it also generates the least energy downrange.
Having spent time with both of these calibers at the range, I find the 10mm/180 kicks only slightly more than the .40/155, not really enough to make much subjective difference to me. However, full power 10mm loads, such as the Winchester 175 grain Silvertip factory load, kick noticeably harder than our comparison loads.
Summary and Conclusion
The 10mm Auto beats the .40 S&W in every performance category except recoil. Given its larger case with greater powder capacity and slightly higher MAP, it could not be otherwise. Even the subjective recoil of the two cartridges with 1180 fps loads is not dramatically different, because the 10mm G20 pistol is slightly heavier and has a wider back strap than the .40 caliber G22, making the G20 more comfortable to shoot. However, the trade-off to a wider backstrap is that shooters with small hands may find the 10mm G20's grip overly large and need to alter their grip to comfortably reach the trigger.
It is clear that the 10mm Auto cartridge is ballistically superior to the .40 S&W cartridge. It is also more versatile and can handle a wider range of loads. Lower pressure .40 equivalent (10mm Lite) loads are easy on 10mm pistols and should increase the lifespan of the gun, compared to shooting ballistically identical loads in a .40 S&W pistol. The .40's only real advantage is its popularity, which leads to a greater availability of pistols and lower cost ammunition.
Copyright 2012 by Chuck Hawks. All rights reserved.