The 10mm Auto and .45 ACP are the most powerful, commonly available, big bore cartridges designed for autoloading pistols. Thus, a comparison of the two was inevitable.

10mm Auto

The 10mm Auto was introduced in 1983 by Norma. 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 accuracy of the Glock 20's we have tested is good, better on average than the .45 ACP pistols we have tested.

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 and the 10mm Auto is probably most useful with the caliber's heavier bullet weights, usually 175-200 grains.

The Winchester Super-X 175 grain Silvertip offering, one of 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.

.45 ACP

The famous .45 Automatic Colt Pistol cartridge was designed by John Browning in 1905 for a prototype service pistol. The U.S. Army tested both the pistol and cartridge and requested some changes, including a heavier bullet (the original weight was 200 grains). Browning changed the bullet weight to 230 grains at 850 fps and the .45 ACP as we know it today was born. The Army adopted both the cartridge and the Browning designed Colt pistol in 1911 and both are still going strong today.

The .45's best one shot stop percentage is 94% with Federal 230 grain Hydra-Shok bullets, which is a very high number. Other good .45 ACP loads are the Cor-Bon 185 grain JHP at 92%, the CCI 200 grain JHP at 88%, the Federal 185 grain JHP at 87% and Remington +P 185 grain JHP at 86%. Not all pistols will feed all loads and some, including Government Issue M-1911 pistols, may not reliably feed anything but 230 grain ball (FMJ) ammo. Modern pistols, like the Glock and SIG, are usually reliable with JHP ammo, but it is wise to shoot any .45 ACP pistol extensively with whatever ammunition is chosen for self-defense to verify its reliability.

Modern .45 ACP factory loads usually come with 185, 200 or 230 grain bullets, in JHP and FMJ styles. Unless you are stuck with a .45 pistol that will feed nothing but ball ammo, use JHP bullets for self-defense. Because 230 grain FMJ ammo is cheaper than JHP ammo, and because the .45 ACP is an expensive caliber to feed under the best circumstances, I recommend selecting a good 230 grain JHP bullet for self-defense and practicing mainly with cheaper 230 grain ball ammo. This avoids having to re-zero your .45 after every practice session. Anyway, most .45's have fixed sights, regulated for the 230 grain bullet, and cannot be re-zeroed for other loads.

The typical factory load for the .45 ACP uses a 230 grain bullet (either FMJ or JHP) at a published muzzle velocity (in a 5" barrel) of 850 fps with 370 ft. lbs. of muzzle energy. Because the .45's short, fat, slow bullet falls pretty fast as the range lengthens, outdoorsmen are better off carrying something else in the field, such as a magnum revolver or a 10mm Auto pistol.

The Comparison

To represent the .45 ACP, we will use two factory loads, standard pressure and +P. The Hornady +P Custom 200 grain XTP-JHP factory load is representative of +P offerings. For a standard .45 load, we will use the Hornady 230 grain FMJ-RN offering, which is typical of the 230 grain ball ammo supplied by all of the major ammunition manufacturers. To represent the 10mm Auto, we will use the Hornady Custom 180 grain XTP-JHP factory load. This is not the hottest 10mm load available, but it is typical and has the advantage of using the same type of bullet (XTP) as our +P .45 load. Hornady XTP loads are widely considered a good choice for self-defense. Hornady ballistics for all three of these loads was developed in 5" barrels. We will compare these factory loads in velocity, energy, trajectory, sectional density, bullet diameter and recoil.

Velocity

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.

• 10mm, 180 grain XTP: 1180 fps MV, 1077 fps at 50 yards, 1004 fps at 100 yards
• .45 ACP, 200 grain XTP: 1055 fps MV, 982 fps at 50 yards, 926 fps at 100 yards
• .45 ACP, 230 grain FMJ: 850 fps MV, 818 fps at 50 yards, 788 fps at 100 yards

As these figures reveal, the 10mm Auto has a worthwhile velocity advantage over the .45 +P at all ranges and a substantial advantage over the standard velocity .45 ACP load.

Energy

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 when comparing similar calibers and loads. Here are the energy figures in foot-pounds (ft. lbs.) for our comparison loads at the muzzle (ME), 50 yards and 100 yards.

• 10mm, 180 grain XTP: 556 ft. lbs. MV, 464 ft. lbs. at 50 yards, 403 ft. lbs. at 100 yards
• .45 ACP, 200 grain XTP: 494 ft. lbs. MV, 428 ft. lbs. at 50 yards, 380 ft. lbs. at 100 yards
• .45 ACP, 230 grain FMJ: 369 ft. lbs. MV, 342 ft. lbs. at 50 yards, 317 ft. lbs. at 100 yards

The 10mm emerges as the clear winner in the energy sweepstakes, particularly when compared to the standard velocity .45 ACP load. The .45 +P load comes reasonably close to the 10mm in energy, although it, too, remains inferior at all ranges.

Trajectory

Velocity and ballistic coefficient (BC) are the factors that primarily determine a bullet's trajectory. The BC of our 10mm (.40 caliber) 180 grain XTP bullet is 0.164, the BC of the .45 caliber 200 grain XTP is 0.151 and the BC of the .45 230 grain RN is 0.184.

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 like the 10mm, 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, which is common for handguns. Here are the approximate trajectories for our comparison loads from 25 yards to 100 yards.

• 10mm, 180 grain XTP: 0" at 25 yards, -1.2" at 50 yards, -10.3" at 100 yards
• .45 ACP, 200 grain XTP: 0" at 25 yards, -1.3" at 50 yards, -10.9" at 100 yards
• .45 ACP, 230 grain FMJ: 0" at 25 yards, 2.3" at 50 yards, -16.8" at 100 yards

The standard 10mm Auto load shoots slightly flatter than the .45 +P load and both shoot much flatter than the standard pressure, 230 grain .45 ACP load, to which the term "rainbow trajectory" clearly applies.

Sectional Density

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). Here are the SD numbers for our three bullets.

• 10mm, 180 grain XTP-HP: 0.161
• .45 ACP, 200 grain XTP-HP: 0.140
• .45 ACP, 230 grain FMJ-RN: 0.162

The 10mm/180 and .45/230 grain bullets are nearly identical in SD. The 200 grain .45 bullet is inferior to both by a considerable margin. Other factors being equal, this bullet's penetration should be limited in comparison to the heavier for caliber bullets.

Bullet Diameter

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. Here are the actual bullet diameters of our two cartridges.

• 10mm Auto: .400"
• .45 ACP: .451"

The .45 ACP has a clear advantage over the 10mm in bullet diameter and should produce a wider wound channel.

Recoil

The most popular 10mm service pistol is the Glock 20. It is hard to say what is the most popular pistol chambered for the .45 ACP, but Glock also offers their large frame autoloader in .45 ACP, as the very popular Model 21. The G20 weighs approximately 2.44 pounds with a loaded magazine and the G21 is similar. This is the gun weight we will use when calculating the recoil of our comparison loads.

• 10mm, 180 grain XTP at 1180 fps: 8.3 ft. lbs. energy, 14.8 fps velocity
• .45 ACP, 200 grain XTP at 1055 fps: 8.0 ft. lbs. energy, 14.6 fps velocity
• .45 ACP, 230 grain FMJ at 850 fps: 6.6 ft. lbs. energy, 13.2 fps velocity

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 heavy recoil, as autoloading pistols go, but the 10mm kicks lightly harder than the .45 +P. However, the difference is slight and may not be noticeable to most shooters. The low velocity .45/230 grain ball load, naturally, generates the least recoil. It is, of course, by far the least effective of our comparison loads, suitable primarily for relatively inexpensive practice.

Summary and Conclusion

The .45 ACP's greatest advantage over the 10mm Auto is the availability and wide distribution of .45 guns and ammo. The .45 is one of our most popular handgun cartridges and there are a great many pistols offered in the caliber. The 10mm Auto, on the other hand, has remained more of a "specialty" cartridge and ammunition and pistols are typically available only from actual gun shops. Big box department stores with sporting goods departments seldom stock 10mm pistols and ammo.

Our comparison shows that, ballistically, the standard 10mm Auto is somewhat superior to the .45 ACP +P load and way ahead of the standard pressure .45 load in everything save bullet diameter/cross-sectional area and recoil. Even in recoil, the .45 +P load's advantage over the 10mm is very small. The only possible conclusion is that the shooter looking for superior ballistic performance in a big bore pistol cartridge would do well to choose the 10mm Auto over the .45 ACP.