In the 1980s and 1990s, it looked like the .45 ACP’s days might be numbered. Everyone from the U.S. military to local police departments was jumping ship in favor of cartridges like the .40 S&W, .357 SIG, and 9mm. While die-hard 1911 fans and a few SOF guys stuck with the classic American round, all indications were that the fat, slow .45 was about to take a backseat in the handgun cartridge world. Then along came a curveball from Austria, of all places, in the form of the Glock 21, the gunmaker’s first .45 ACP offering.
The full-sized polymer-framed, striker-fired gun looked and functioned like all the other Glock models at a time when the company was building a reputation as the future of handguns. Glock’s investment in the .45 ACP market signaled that while the 9mm was on the rise, the United States’ old war horse of a pistol cartridge was by no means being put out to pasture.
In the same way that Chevrolet is somehow keeping pushrod V8s relevant by using one to power the current-generation Corvette to high-speed glory, Glock saw a market for modern striker-fired pistols slinging America’s most storied handgun cartridge. And many gunmakers followed suit, releasing .45 ACP versions of their most popular handguns even through the Wonder Nine era.
But would the combination be a marriage made in heaven or a soup sandwich?
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Modern Pistol Meets Classic Cartridge
The first Glock 21 dropped in 1990, building on the success of the full-size Glock 17 and compact Glock 19 — both chambered for 9mm. By this time, Glock was two years into production of its second-generation pistols.
The all-new .45-caliber Glock 21 shared its full-size (standard, for those who speak Glock) frame with the 10mm Glock 20 but mated it to a caliber-specific slide assembly. In this first batch, the Glock 21 Gen2 came without a frame-mounted accessory rail.
Early reviews praised the Glock 21’s low bore axis, lightweight polymer frame, striker mechanism, and trigger safety — features that were so well-received they’ve since become ubiquitous in the modern pistol market.
Interestingly, one reviewer dismissed the Glock 21’s checkered trigger guard, declaring that “those who fire from the correct Weaver position will not employ this useless feature.” The same article predicted that the .45 ACP would dominate the market and the 9mm would fall by the wayside. Hey, nobody’s right all the time.
The Glock 21 may not have been as satisfying to shoot or as aesthetically pleasing as other pistols of the day, but it made up for those lacks with a massive leap forward in reliability. Some shooters reported issues with +P ammunition due to case bulging, but the Glock 21 seemed happy to chew any standard ammo, even hollow points, which can be an issue for 1911s in particular, a gun with a feed ramp designed for ball ammo.
Increased magazine capacity and decreased weight also made the full-size pistol easier to carry than most of its competition.
The Glock 21 gradually evolved alongside the manufacturer’s other models with Gen3, Gen4, and the current Gen5 MOS updates.
Glock’s big .45 never enjoyed the same widespread success as the Glock 17, and it has fallen off in popularity among civilian Glock fans who have moved toward 10mm Glock models, but it has seen varying degrees of use by the military and law enforcement bodies.
With 9mm pistols remaining the standard for official use (see the U.S. Army’s adoption of the SIG Sauer M17), don’t hold your breath for the Glock 21 to gain ground as a duty pistol. It’s still an excellent personal defense option, though, if you trust the stalwart .45 ACP, and I don’t expect to see it leave showrooms anytime soon.
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Field Stripping the Glock 21
Except for internal components that most owners should never mess with, the Glock 21 looks, feels, and functions like every other Glock. It’s a polymer-framed, striker-fired pistol with an integrated trigger safety — there’s not much to adjust to if you’re new to the platform.
You may notice a little extra heft because the Glock 21 needs a larger frame than its 9mm counterparts to accommodate a stack of .45 ACP rounds. It’s still slim and light compared to other big-bore pistols, though.
As is typical of Glocks, the Glock 21 is extremely easy to maintain and takes just a few seconds to take apart. With an unloaded and cleared pistol, all you have to do is pull the trigger, retract the slide just enough to relieve the pressure on the take-down tabs, depress the tabs, pull the slide forward off the frame, then pop out the recoil spring, guide rod, and barrel. Field stripping and maintenance don’t get much easier than that.
Glock 21 Gen5 MOS Specs
Caliber: .45 ACP
Frame size: Standard
Grip: Polymer
Capacity: 13+1
Action: Striker-fired
Barrel length: 4.6 inches
Optic ready: Yes
Safety: Safe Action trigger system
Weight: 39 ounces (with a loaded magazine)
MSRP: $700
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Glock 21 Gen 5 MOS vs. Glock 21 Gen4
Glock began rolling out its fifth-generation pistols in 2017. Initially, only the 9mm Glock 19 and Glock 17 (the company’s perennial sales leaders) got Gen5 updates, but the improvements eventually made their way to other models, including the Glock 21.
The biggest functional improvement to the Glock 21 Gen5 MOS is the Modular Optic System. By using adapter plates instead of mounting optics directly to the slide, Glock allows owners to choose among red dot optics with different mounting platforms. If you want to keep it old school, there are three traditional sights available: polymer, steel, and night sights.
Cosmetically, little has changed in the Glock world over the past several decades. For Gen5 pistols, Glock ditched the grip’s controversial finger grooves, added a slightly flared magazine well, relocated the take-down tabs a few millimeters to the rear, coated the slide with an nDLC finish, and strengthened the trigger mechanism to eliminate the need for a second pin to support the locking block.
Most of the Gen5 changes are internal. The barrel gets traditional rifling instead of polygonal rifling, and the trigger assembly is entirely new. Almost every other internal component has been tweaked, so very few parts are compatible across Gen4 and Gen5 pistols.
Older Gen4 versions of its pistols are still available for you to buy. Picking one up is an excellent way to save money if you can do without some of the current bells and whistles. At the time of writing, it will cost you about $150 less to buy a Glock 21 Gen4 than it will to get your hands on a new Glock 21 Gen5 MOS.
Another option for shooters who prefer the Glock 21 Gen4 is the Glock 21 SF. This short-frame variation has a slimmer receiver that’s designed to be more comfortable for people with small hands.
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Does the Glock 21 Have a Place in the Modern Handgun World?
Considering the die-hard followings of Glock and the .45 ACP cartridge, it seems like the Glock 21 should be selling as fast as the Smyrna, Georgia, assembly line can churn it out. Unfortunately for Glock’s sales figures, those two passionate fan bases don’t overlap all that much.
Instead, the Glock 17 is the brand’s top dog when it comes to full-size pistols. While the two are nearly identical in physical size, except for grip circumference, the Glock 17’s standard magazine holds 17 rounds compared to the Glock 21’s standard 13-round magazine, which is still pretty good for a .45 these days. The S&W M&P 2.0 in .45 ACP holds only 10+1 rounds, for example. The single-stack SIG Sauer P220 holds only 8+1. The .45 is a fat cartridge, and that simply doesn’t make for a lot of magazine space, no matter how well it’s engineered.
Then there’s the weight. Even with four more rounds in the hopper, the G17 is 4 ounces lighter than the G21. Add in the ballistic advantages of 9mm over .45 ACP, and the Glock 17 looks like a better alternative for most people.
So if you’re going to accept .45 ACP’s inherent drawbacks compared to 9mm, why not go full ‘Merica Mode and get a 1911? After all, John Browning’s most enduring design offers a more comfortable grip, arguably the best trigger in the business, and visual appeal that blurs the lines between machine and art.
In this case, the Glock has a leg up in terms of practicality. Despite owning two World War championship titles, all but the highest-end 1911s are simply not as reliable as the Glock 21, and the capacity of the 1911’s single-stack magazine is an issue for a defensive or duty pistol.
Now, as in 1990, the Glock 21 occupies a happy middle ground between popular platforms. It offers world-famous reliability and 13+1 capacity that you can stretch with Glock extended magazines. The .45 ACP cartridge still has undeniable utility as a defensive round that can get the job done with less risk of overpenetration than the speedy 9mm, and it’s much easier to source than Glock’s proprietary .45 GAP.
If you’re set on getting a pistol chambered for .45 ACP, it’s hard to argue against the Glock 21. By combining legendary Glock reliability, an optics-ready slide, and a full-size frame capable of harnessing the big pistol cartridge, the Glock 21 Gen5 MOS isn’t merely relevant; it’s the best .45-caliber Glock you can get.
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