Gen 4 magazines can be used in any generation of Glock pistol, however you must use Gen 4 magazines in a Gen 4 Glock if you want to switch the gun from a right-handed magazine release to a left-handed release.
Use only Glock factory magazines. There are a number of knockoff, aftermarket magazines available on the market. Currently Glock magazines are inexpensive and plentiful. There isn’t any reason not to use the real thing.
You can use the high-capacity 33-round 9mm and 31-round .40 S&W magazines in full-size (Glock 17 & 22) and compact-size (Glock 19 & 23), however these magazines may or may not be reliable in the sub-compact frame (Glock 26 & 27) pistols.
You can use any caliber appropriate magazine in any smaller version Glock than what the magazine was originally intended for (with the exception of the new single-stack Glock 43). Example: In a subcompact Glock 26 you can shoot larger Glock 19 or 17 magazines. A compact Glock 19 can use magazines from a full-size Glock 17.
If you add a magazine extension intended to add two rounds to 9mm magazines or one round to a .40 S&W magazines, you will not have to change springs in subcompact magazines (Glock 26 & 27), you will need to use a spring intended for 17-rounds with compact size magazines (Glock 19 & 23), and if you want to add the extension to full-size magazines (Glock 17 & 23) you can order directly from Glock a spring that is intended to push 19-rounds. Only use genuine Glock parts, including the extension.
If you don’t have the patience for a detailed explanation, then you will still be well served by the information above. If you want to know more, keep reading.
Glock Magazine Essentials:
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Gen 4 Magazines in Gen 4 Glocks:
With a “Gen 4” Glock you can reverse the magazine release to the right side of the pistol so that it can be operated by left-handed shooters. Any appropriate caliber and size magazine will work in a “Gen 4” Glock when used with the magazine release traditionally mounted on the left side. Should you choose to reconfigure your pistol for left hand shooting you will have to use the newest “Gen 4” magazines that have a notch on both the left and right side of the magazine (as seen in the photo to the right). The older magazines will not lock into the pistol.
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Khan Korean Military Contract Magazines:
Stay away from the Khan “Korean Military Contract” (seen right) or any other aftermarket magazines for Glocks. Factory Glock magazines are too plentiful and inexpensive for you not to buy the real thing.
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Using Larger Frame Magazines in Smaller Frame Pistols:
Magazines from larger Glocks will work in smaller Glocks of the same caliber. Example: The G17 17-round magazine will fit and function in the G19 and G26. The .40 S&W G22 magazine will fit and function in the G23 and G27. The higher capacity magazines will hang out of the bottom of the magazine well, but it will work.
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33-Round (9mm) & 31-Round (.40 S&W) Magazines:
The 33-round 9mm magazines (seen far left in the photo below) are intended for the fully automatic G18 machine pistol. They will fit and function in the G17 and G19. You can run into reliability problems if you try to use the huge magazine in the baby Glock (G26). The same applies to the 31-round .40 S&W magazines. It will fit and function in the G22 and G23, but may not function as well in the small G27.
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Adding Pinky Finger Extensions on Compact Glock Magazines:
If you want to add a pinky-finger extension to the flush fitting magazines of a compact Glock (G26, G27, G30, G33) Pearce Grip makes a durable extension that has survived countless mag drops to the ground and has survived being carried on fully loaded magazines for years.
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Adding Magazine Extensions That Add Magazine Capacity:
If you are going to a magazine extensions that increase the magazine’s capacity I recommend that you only use Glock’s own extensions. There are several aftermarket extensions. I had one added to a G26 magazine. The fully loaded magazine was loaded in the pistol. The pistol was sitting in its holster on my desk while I was working. Without warning the rim of the magazine extension that holds it to the magazine broke loose. The magazines spring shot the extension off of the pistol like mousetrap and bullets flew out everywhere. It scared me to death. Thanks God that it didn’t happen while I was standing in line to check out at the grocery store, or was defending myself with that firearm. Glock makes a magazine extension that adds two rounds to their 9mm magazines, and one round to their .40 S&W magazines.
Afterthought: Since writing the above information I have come across a number of horror stories of magazine extensions popping off the magazine without warning and spilling rounds all over the ground. There were several contributions by police officers and civilians that knocked the extension off while carrying a holstered weapon while seated in their vehicles, or bumping them while in a scuffle with a perp. There were also a number of stories of magazines popping apart when ejected magazines hit the ground, especially with magazines that were not fully holstered. I’m no longer using magazines with extensions. If I feel a need to carry more ammunition in the gun I’ll carry a longer magazine.
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Changing Springs With Extensions That Add Mag Capacity:
When adding +2 extensions to my 9mm Glock magazines I was concerned that the original magazine spring might not be long enough for the addition length of the modified magazine. I was worried that the springs might not be strong and fast enough with the last couple of rounds in the magazine. I did a bunch of research and found this useful information and recommendations.
Baby Glocks (G26 and G27) use the same springs as the mid-size frame Glocks (G19 and G23). They are the same part number and have the same number of coils. This means that a spring that is good enough for 15-rounds in the G19 is stuffed into a 10-round G26 magazine. It is no problem to simply remove the flush-fitting base plate of the magazine and add the +2 extension.
If you are going to add an extension to a mid-size magazine you should replace the magazine spring with one that is intended for the full-size frame. Example: Replace the 15-round G-19 spring with one intended for a 17-round G17, or replace a 13-round G23 spring with one intended for the 15-round G22 spring. A now modified 17-round magazine will have a 17-round spring, and a modified 15-round .40 S&W magazine will have a 15-round spring.
If you want to add an extension to a full-size G17 or G22 magazine you can order a Glock factory spring that is intended for 19-rounds in the G17, and 16 or 17 rounds in the G22.
The extensions and springs can be ordered from Brownell’s or Midway USA.
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Glock Magazine Followers:
The inner dimensions of the magazine tubes have been changed various times, as well as the followers. They’ve been changed as problems with the previous designs were discovered and to work better with various ammunition. As a result the followers in the magazines have also evolved. You may possess Glock magazines from different time periods (maybe you bought a Glock pistol and magazines several years ago, but you just recently bought some brand new magazines). They will all fit and function just fine in your pistol, but you might notice minor variations with the magazine bodies and followers. If you mix and match parts from several different evolutions of magazines you may run into reliability issues.
Periodically you may choose to disassemble your magazines to thoroughly clean them (such as after operating in a dusty or muddy environment). It is recommended that you only disassemble and clean one magazine at a time so that you do not accidentally reassemble parts from different evolutions of magazines. Remember that your magazines should be dry without any traces of oil or chemicals which might leech into the primers of your ammunition and cause reliability issues.
If you choose to rehabilitate older magazines and replace springs and followers you will need to identify what evolution of follower and then research online as to what new versions are compatible with your older magazine body. You can identify the caliber and evolutionary version by engravings on the follower. The followers shown right are .40 S&W and are evolution #5.