The 10mm Cartridge

Developed in 1983 as a law enforcement cartridge and originally adopted by the FBI, the 10mm was designed to deliver exceptional stopping power in a smaller caliber than .45 ACP. While 10mm sounds like a bullet that is just one little bitty millimeter larger than a 9mm, the 10mm packs a wallop that gave everyone pause because of its higher chamber pressures and heavier recoil. Yes, less than a .45 ACP cartridge, but still a handful for many. It has something to do with Newton’s third law: “For every action, there is an equal and opposite reaction.”

The 10mm had a brief turn with the FBI as most agents found it too harsh of a round. Similar complaints occurred in other sectors of law enforcement and the 10mm finally gave way to the most commonly used cartridge today, the .40 S&W. While several ammunition manufacturers produce the 10mm, including Federal, Remington, Winchester, Hornady and CorBon, the guns chambered for this high-power round have diminished over time. Glock has managed to tame this wildcat with a full-size semi-auto that allows optimum firepower without some of the abuses of harsh recoil, making the 10mm a very viable cartridge for personal defense.

Enter the Glock 20

The Glock 20 was first introduced in 1990, some seven years after the cartridge debuted, and is available in the SF “Short Frame” version (tested), and in a ported barrel Glock 20C version. The latter is ideal for competitive shooting. A 10mm is a big bullet (0.4 inches diameter) in a big cartridge case (1.25 inches), and is usually loaded in a 180-grain weight (the range is 135 to 200 grains). Comparatively, the 10mm dwarfs the popular semi-auto 9mm round that was once the darling of law enforcement, which still remains the standard U.S. military pistol cartridge.

My first test drive with the GLOCK 20 in 10mm AUTO took place on a cold winter’s day in 1991. A box containing the gun appeared on my desk. I had been looking forward to checking out this new pistol. The next day, I beat a hasty path to my agency’s range where I found the GLOCK 20 to be a superb performer and the perfect launcher for the hard-hitting 10mm AUTO cartridge.

The GLOCK 20 was the first of the Austrian manufacturer’s large-frame pistols. It appeared on the scene a few months prior to the GLOCK 21 in .45 AUTO. At the time, the .40 cartridge hadn’t yet caught on, and there was still considerable interest in 10mm AUTO for law enforcement use. Endorsement of the 10mm AUTO cartridge by the FBI, albeit in an attenuated load, made this cartridge a serious contender in police circles. The new GLOCK pistol quickly proved it could handle the FBI-spec reduced-velocity load as well as the high-test offerings that deliver performance on par with mid-bore magnums.

Engineered To Be Efficient

Although the Glock 20 is a full-size service pistol, it does epitomize size efficiency. The 10mm AUTO cartridge is indeed a big stick, with the hottest loads developing over 700 foot-pounds of muzzle energy. Unlike some “crew-served” self-loaders chambered for rimmed-case magnum revolver cartridges, practical-sized pistols appropriate for uniformed law enforcement or concealed carry can be built around the powerful 10mm AUTO. With a total capacity of 16 rounds, external dimensions no larger than some 9x19s, and a weight of just a tad over 30 ounces, the Glock 20 represents all the fun you can pack into a readily portable package.

In the grand scheme of things, the Glock 20 is on my short list of particularly useful pistols. For everyday concealed-carry use, I prefer my GLOCK 19. If I were to spend considerable time in the outback on some modern-day Indiana Jones adventure, the Glock 20 would get the call. With the right load, the Glock 20 could easily handle any problem, whether it walks on two legs or four.

As much as I like the standard Glock 20, it’s right on the ragged edge of efficiency for my medium-size hands. Shooters with smaller hands may find it outside the limits of practicality. But fair reader, there is a fix.

Glock Introduces the Short Frame

Early in the 21st century, GLOCK introduced the SF (short frame) version of the highly popular GLOCK 21 .45 AUTO. The SF variant of the GLOCK 21 featured reduced grip circumference and trigger reach to better accommodate a wider range of hand sizes. In 2009, GLOCK applied the same technology to the Glock 20 and Glock 29, both chambered for the 10mm AUTO. The GLOCK 20 SF, for many shooters, holds a number of advantages over the original.

Gun Details

Like all GLOCK pistols, the Glock 20 SF is built on a durable polymer frame that is lightweight yet super tough. Grip circumference is slightly less than that of the original large-frame pistols. It doesn’t quite approach that of the GLOCK 17 series, but the reduction will definitely make a difference for some shooters.

Grip

Reduced grip circumference will allow more shooters to achieve optimum finger placement on the trigger. Quite frankly, if this isn’t happening, there is no way you can be at the top of your game. Extended trigger reach causes shooters to shift their grip to compensate, pulling shots off-center and increasing felt recoil, all degrading performance. Without question, the SF treatment on the Glock 20 will help some shooters perform at a higher level.

Accessory Rail

As with all recent-edition GLOCK service size and compact pistols, an accessory rail has been molded into the dust cover area of the frame. While the original GLOCK 21 SF featured a mil-spec Picatinny rail, newer pistols are set up with the universal rail. Adding and removing a wide range of tactical illuminators and laser aimers is easy.

Glock-Specific Extras

Other details are common to various GLOCK pistols. The gun tested came through with the five-pound connector, which makes it extremely “shootable,” particularly when firing at speed. Three passive safeties are incorporated into the pistol. These include a trigger safety, firing pin safety and a trigger mechanism housing safety that combined prevent the gun from firing out of battery. Newer GLOCK pistols also feature a raised surface on the extractor. When a round is chambered, the extractor no longer sits flush with the slide, and condition is easily verified by feel, even in the dark. Sights on the sample pistol were the fixed combat style with a white outline rear unit, drift adjustable for windage. Mated to the rear sight was a white-dot front. Adjustable sights and tritium night sights are available as factory options.

The slide and barrel of the GLOCK 20 SF are crafted from steel and finished in hardwearing black Tenifer. The Tenifer finish is extremely hard and just about impervious to rust. Constant exposure to saltwater environments has yet to create issues with my agency’s GLOCK pistols. There is no more robust factory finish than that offered by GLOCK.

Barrel

The barrel on the GLOCK 20 SF measures 4.6 inches in length and sports hexagonal profile rifling with a right-hand twist. Hexagonal rifling is less susceptible to wear than conventional lands and grooves. And, due to a better gas seal, delivers higher velocities.

Frame

The trademark polymer frame keeps weight down to a trim 30.71 ounces, including the empty magazine. Time has illustrated that the GLOCK polymer frame is equal to one of steel in durability and superior to aluminum alloy. Besides the obvious weight savings, the polymer frame also transmits less felt recoil to the hand, an important quality with a powerful cartridge like the 10mm AUTO.

Range Time

Having shot the GLOCK 20, I didn’t experience any surprises shooting the SF model—and that’s a good thing! Shooting qualities were first rate, and the test pistol proved entirely reliable through my evaluation.

One issue on many shooters’ minds is that ever-subjective quality of felt recoil. Indeed, there is a bigger bump than firing a 9×19, but the Glock 20 SF dissipates the transmission of felt recoil to the hand. With full-house 10mm AUTO loads, you definitely know when the pistol goes off, but I wouldn’t categorize the sensation as unpleasant.

“Bill Drills”

In order to see what sort of affect the 10mm AUTO cartridge might have on combat performance, I couldn’t resist running the Glock 20 SF through a number of “Bill Drills” (five shots, 5 yards, very fast!). Test ammo was CC1-Blazer 200-grain TMJ. It runs a bit warmer than the Fed-Lite load but isn’t as snappy as the hot stuff. The name of the game was to shoot as fast as possible while keeping all the hits inside the Primary Neutralization Zone (PNZ) of the DST-CB from Law Enforcement Targets.

My elapsed times ran between 1.97 seconds to 2.18 seconds. Hits were well centered, and I didn’t find the Glock 20 SF to be any more difficult to manage than my like-sized pistol in .45 AUTO. Simple physics prevents me from running the new SF as fast as my GLOCK 19 in 9×19, but this big 10mm AUTO can be easily managed by any seasoned pistolero. I would categorize felt recoil and muzzle rise of the high velocity 10mm loads tested to be on par with that of .45 AUTO +P.

Shooting from the Bench

From the bench, five different 10mm AUTO loads were fired to assess accuracy potential. Five-shot groups were fired from a distance of 25 yards with the aid of a Hornady Delta Rest. Groups were measured to the nearest 0.125 of an inch and results averaged.

Best results were posted with Remington’s 180-grain subsonic JHP, which averaged a tight 2.375 inches. Other loads tested were in the 3- to 4-inch range, and I was not able to duplicate my effort with the Remington load. On the plus side, I was able to reliably tag a steel head plate set 25 yards distant from unsupported standing, illustrating that the Glock 20 SF is plenty accurate enough for any real-world application.

Running the same loads through an Oehler 35P chronograph also proved thought-provoking. Winchester’s 175-grain Silvertip zipped along at over 1,200 feet per second and would be a formidable self-defense load. This is within shouting distance of the 175-grain Silvertip I favor in my .41 Magnum revolver. Comfort factor in the GLOCK is much enhanced. Another solid contender for self-defense is CorBon’s 155-grain DPX hollowpoint. The round features an all-copper high performance bullet from Barnes and moderate recoil.

Final Notes

After putting the original GLOCK 20 through the paces back in 1991, I christened the fire-breathing pistol the “GLOCKzilla.” The lightweight, high-capacity Glock 20 had it all over competing 10mm AUTO designs, and this remains true to this day. And, the Glock 20 SF proves to be even better.

The 10mm AUTO cartridge has lost quite a bit of ground to the .40. It has virtually disappeared from the law enforcement scene. That’s too bad. The 10mm AUTO can exceed the performance of the .40 in every way, but that all comes with a price. To pay it, the 10mm AUTO requires a larger and slightly heavier platform. Most consumers prefer the convenience of the smaller .40 built on the 9×19 frame.

But if size isn’t an issue, the GLOCK 20 SF has got it all going on. As indicated earlier, the reduced grip circumference can only add to its appeal. It is more user-friendly than any of the magnum revolvers. Its raw horsepower is only eclipsed by the heavier .41 and .44 Magnum loads.

The 10mm AUTO can effectively take medium-size game animals such as deer and boar, and even larger critters. Even with medium-velocity loads, the 10mm AUTO is an extremely formidable self-defense round. The Glock 20 SF might breathe some new life into this overlooked cartridge.

The 10mm AUTO will continue to enjoy a cult following in the years to come. This cartridge deserves a better fate. The GLOCK 20 SF may acquaint a new legion of shooters with its superior performance.

For more information on the Glock 20 SF, visit us.glock.com.