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Glock 21SF (Police Trade-In) Review

Two years ago, I found myself tight on funds and in need of a .45 ACP suppressor host for my work with Silencer Shop. Now if you’re a handgun enthusiast, you probably know that threaded .45s come at a premium. In fact, it isn’t unusual for people to drop $1,000 or more on such a firearm. My budget was far more limited but I still wanted something that I could count on to work reliably during my suppressor reviews.

After weeks of shopping, I kept coming back to the same few options, but was mostly drawing blanks. I previously tried to add a threaded barrel to my 1911 and the results were less than satisfactory from a reliability perspective. Still, at the top of my very short list was the Glock 21. As with many models of Glocks, police trade-in examples of the 21 are rather common at gun shops and online dealers. These used pieces are typically in good working order, but might feature moderate holster wear. Former police Glocks frequently fetch less than $400.

Knowing that I wouldn’t like the bulky grip of the standard 21, I sought out the “Short Frame” 21SF. The primary difference between the two is that the 21SF’s grip is shorter from backstrap to frontstrap, making it more manageable for those of us with average-sized hands. The SFs are less common as the trade-ins than full Glock 21s, but I did manage to find one in very good condition from Shoot Straight in Florida for around $420. After years of hipster-esque resistance, I finally hopped on the Glock bandwagon.

Glock 21SF Magazine Loaded
The Glock 21SF is the "Small Frame" model of the .45 ACP Glock 21. By default, it uses a 13-round magazine.

Technical Details

At its heart, the Glock 21SF is a Browing-style cam action pistol like most other popular handguns. When a round touches off, the pressure behind the bullet pushes rearward against the pistol’s breech face, causing the slide to travel backwards. However, since the pressure inside the barrel is still too high at this point for the action to safely open, the barrel also travels a short distance (approximately 1/4″) rearward with the slide. At this point, the pressure inside the chamber has dropped to a safe level and the lug on the underside of the barrel contacts a small piece inside the pistol’s frame. This piece causes the chamber to rotate downward, unlocking the barrel from the slide. The slide then continues rearward; ejecting the spent casing, partially cocking the striker, and fetching the next round before returning to battery.

Since Glocks are striker-fired pistols, they lack an external hammer (or any hammer for that matter). Rather, a small, spring-loaded metal piece (the striker) performs dual duty as both a hammer and a firing pin. With the pistol in battery, the striker spring is only around 75% compressed. As the shooter pulls the Glock’s trigger, a long metal piece called a connector pushes the striker further back until the spring is 100% loaded. Any further pressure on the trigger then causes the connector to drop, releasing the striker and firing the pistol. This mechanism gives striker-fired pistols like the 21SF a unique trigger pull that feels like a blend of traditional double- and single-action triggers. It is worth noting that Glocks lack any sort of double-strike capability. The slide must be at least partially cycled to reset the striker.

Glock 21SF Connector
The connector is the small arm that can be seen below the magazine well in this photo.

The Glock line of pistols was the first family of truly successful polymer-framed handguns. While the top half of any Glock is mostly steel, the frame is manufactured using a blend of Nylon 6 and glass filament. This makes the Glock 21SF quite a bit lighter than a standard 1911 ( 29 ounces vs. 41 ounces unloaded). The proprietary mixture is also resistant to heat and most solvents and is strong enough to withstand the recoil of popular handgun rounds. To prevent breakage, the frame’s internal slide rails are steel reinforced.

Speaking of the 1911, the 21SF is similar to Browning’s classic in overall size. It’s obviously thicker than the single-stack gun, but the Glock’s slide and grip lengths are very close. Generally speaking, if you can comfortably carry a 1911, you can probably carry a Glock 21SF.

Glock 21SF Grooves Accessory Rail
The finger grooves and accessory rail were new features added to the Gen 3 Glocks.

My 21SF is a Generation 3 (Gen 3) pistol. So far, Glock has released five generations of their popular handguns, but not every model is represented within every generation. Gen 3 pistols are operationally similar to Gen 2 guns, but feature finger grooves on their front straps to prevent slipping. Gen 3 guns also debuted Glock’s proprietary accessory rail. Gens 4 and Glocks are substantially different than Gen 3 models in that they feature interchangeable backstraps, more aggressive grip texturing, and two-part recoil springs.

The most controversial aspect of any Glock is the lack of a manual safety. For this reason, I typically don’t recommend these guns to new shooters There are several safety features on Glock pistols, including a trigger safety, a firing pin safety, and an internal drop safety. The partially cocked striker also lacks sufficient energy to dimple a primer if it happens to fall. Still, I would rather equip new shooters with a pistol that has a manual safety lever as the four safety rules sometimes take time to truly sink in.

While I’m on a roll, I might as well come out and say that I hate the way Glocks come apart for cleaning. To field strip the 21SF (and other Glocks), pull the slide rearward approximately 1/4″ and pull down on the disassembly lever on the frame, just forward of the trigger. With the lever depressed, release the slide and pull the trigger (make sure the gun is unloaded) to unlock the upper half of the pistol. Frankly, I hate that Glocks require shooters to pull the trigger during disassembly. While careful and attentive handling of the firearm goes a long way in preventing negligent discharges, things happen and I firmly believe other manufacturers have taken better approaches to field stripping.


Classic, Austrian Glocks like this Glock 21SF feature Tenifer-treated slides that wear very nicely. Like Melonite, Tenifer is a nitrocarburizing process that penetrates steel and adds abrasion and corrosion resistance. Up until 2010, Glock used Tenifer (followed by black Parkerizing) on all of its pistols’ slides and barrels. Now, the company uses a slightly different method of nitrocarburizing that many feel is less durable than the past Tenifer process.

Glock 21SF Tennifer Finish Slide
This is a used gun, but in my opinion, it still looks great. The Tenifer slide finish holds up very well.

Among those who know me, it is no secret that I like to keep my firearms (and most other things) clean and free of the nicks and scratches that often come from regular use. With my Glock 21, a pristine pistol was out of the question. However, the wear that is present on the gun’s slide is minimal and the penetrating Tenifer has prevented any sort of corrosion.

I’m less satisfied with the appearance of the 21’s nylon frame. While Glock apparently employs glass-filled Nylon 6, the specific composition used by the company seems more wear prone than the polymers used by other manufacturers. As you can probably see in the images, my 21SF’s frame exhibits numerous shiny spots from hand and holster wear. This is typical of Glocks and in reality is pretty minor, but these Austrian workhorses seem to show more obvious frame wear than the Smith & Wesson and Heckler & Koch police trade-ins I’ve seen.


Factory Glocks (excluding the new threaded versions) generally ship with one of two sight arrangements. Police guns like mine almost always come with 3-dot, post and notch, tritium-illuminated night sights. Since my pistol was manufactured in 2009, my sights still have quite a bit of life left in them and subtly shine green in dark settings. With the sights aligned, there is only a sliver of space on either side of the front post, making the set surprisingly precise.

Glock 21SF Police Night Sights Tritium
Police-issued Glocks like this typically come with tritium 3-dot night sights.

Standard Glock sights are also post and notch arrangements, but rather than featuring dots on the rear part, the stock sight sports a white U-shaped highlight that embraces the rear notch. The front post comes with the familiar white aiming dot. Many people complain about the standard sights, but I’ve found them perfectly usable.


Those of us who live in what some would dub “free states” can expect to find full-capacity, 13-round magazines included with our Glock 21s. In capacity-restricted states, 10-round versions are available. Extensions and aftermarket magazines that bring overall capacity to anywhere between 25 and 30 rounds are available. Factory Glock magazines feature polymer bodies and steel-reinforced feed lips. Since the Glock 21 magazines double stack their .45 caliber payload, they are rather wide. This makes the gun itself wider than some of its rivals.

Glock 21 Magazines Capacity
Standard Glock 21 magazines hold 13 rounds. The 21SF uses the same magazines as the full-frame Glock 21.

The number of magazines included with any particular Glock varies depending on the generation, manufacture date, and whether or not the gun is new or a police trade-in. My 21SF came with three magazines, which seems to be relatively common for former police pistols. New Gen 4 Glocks also seem to ship with three magazines, whereas new Gen 3 models appear to come with two.

Glock 21SF Police Magazines
Adding to the value, police trade-in Glocks like this usually come with three magazines.

Range Report

“Shootability” may truthfully be a meaningless non-word, but I’m going to go ahead and call the Glock 21SF a shootable handgun. What I mean by this is that compared to other pistols, .45 ACP or otherwise, the 21SF is relatively easy to pick up and shoot reasonably well without thousands of rounds of practice. The reasons for this are multifaceted.

The most significant contributor to the Glock’s shooting experience is its trigger. Now, I won’t try to convince you that the factory Glock trigger is anything exceptional. In fact, it’s soundly bested by many newer striker guns, like the Fabrique Nationale FNS, Heckler & Koch VP9, and the Walther PPQ. Still, it is reasonably good. As I mentioned previously, cocking/resetting the Glock leaves its striker in a 75% loaded position. The remaining 25% of the part’s travel occurs on trigger pull, which gives the Glock trigger a springy, but smooth, take-up. After around 5mm of take-up, the trigger comes to a modestly defined wall. After a little under 6 pounds of total pressure have been applied to the bang lever, the striker drops. I’ve heard the Glock’s trigger likened to a staple gun and I don’t think the comparison is off-base. The 21SF’s reset is short (roughly 3mm) and very audible, making it easy to time follow-up shots.

The other thing the 21SF has going for it is its low bore axis. For those unfamiliar with the term, bore axis is the distance, in height, between the barrel’s bore and the top of the shooter’s dominant hand. Looking at the Glock, you’ll notice that the rear of the slide sits very close the primary hand’s web. This reduces the amount of torque generated during cycling and the Glock’s recoil feels more like a “push” than a flip; so staying on target is rather easy. For a relatively light .45 ACP pistol, the 21SF features far less recoil and muzzle flip than I expected.

Despite the 21SF’s tame recoil, I find it to be a better slow fire, accuracy-geared pistol than anything else. For ringing steel and quick target transitions, my 1911 still remains supreme, at least for me. This is probably still a practice issue, but I also believe that the light weight of the 21SF causes me to transition a little too quickly, whereas the heft of the 1911 slows me down enough to steady the firearms and make a more accurate shot. My preferences are subject to change and not necessarily applicable to everyone else.

Ergonomics are the real weak spot for Glocks. It’s true that we all have differently sized hands and varied expectations in terms of comfort, but just about everyone could probably find a pistol out there that is ergonomically superior to the Glock. The grip is blocky; the slide release is small; and the magazine release is even smaller. Even so, the 21SF is a significant improvement over the standard 21. Most notably, the distance from the trigger to the web of the hand is shorter on the SF, as is the size of the hump near the heel of the grip. When I first pulled the 21SF out of its box, I was surprised that it was slimmer than I expected. It’s no 1911, but anyone with medium or larger sized hands should find the Glock 21SF very manageable.

As far as reliability is concerned, the 21SF has been mostly flawless. In its factory configuration, the gun has been perfect over the 300 rounds I’ve fired since acquiring it. As a police trade-in it is impossible to say how many rounds were fired through the gun before I purchased it. With my Lone Wolf threaded barrel, the story has been almost as positive, but not quite. While the Glock cycles fine most of the time, the slide’s return to battery with the Lone Wolf barrel is sluggish. Sometimes when used with a suppressor, this means that the slide needs a little push in order to fully set in battery. I’ll continue to put rounds through this set-up and my expectation is that the barrel simply needs to be further broken in. Otherwise, the Lone Wolf barrel was a perfect drop-in.


Compared to other .45 ACP options, the Glock 21SF really is an excellent choice. Few reasonably sized handguns manage to squeeze 13 rounds of .45 into a magazine, yet the 21 does that and is still surprisingly comfortable to shoot and carry. Former police pistols like mine can be commonly found for $400 or less, putting them on-par, price wise, with budget 1911s and far less proven designs. On top of that, threaded barrels from places like Lone Wolf can be had for just over $100, making the Glock 21 one of the most affordable suppressor hosts on the market. At this point, it is safe to say that I am glad I finally relented and picked up my first Glock.

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