Most Common Glock 21 Gen 4 Problems You Should Definitely Know About

The Glock 21 is a somewhat “soft” shooter. Whether it is due to the frame bending, the enormous surface area of the grip, or something else.

However, the gun wasn’t always cherished. It has a dark side too. The most common problems are: bullet to face, failure to feed issue, magazine issues, slide rattle problem and not firing.

I will discuss the solutions to all these problems and user reviews in this article. So read on till the end!

Features & Specifications of Glock 21 Gen 4:

Barrel Length117 mm
Magazine CapacityStandard: 13
Overall Length205 mm
Caliber.45 Auto
Twist Rate1:15-3/4
SightsSteel three-dot night sights
SafetySafe Action
Dimensions  Width (Overall): 34 mm             Height incl. Mag.: 140 mm
WeightWith empty magazine: 830 g
Trigger Pull28 N
Common Glock 21 Gen 4 Problems and Solutions
Glock 21 Gen 4

Common Glock 21 Gen 4 Problems and Solutions

Bullet to FaceChange to gen 5.
Failure to Feed IssueTroubleshoot components.
Magazine IssuesTroubleshoot magazine.
Slide Rattle ProblemTroubleshoot slide rails with tightening tools.
Not Firing IssuesTroubleshoot spring.

Bullet to Face

The bullet would land on top of your head, hitting the forehead, neck and shoulders.

Doesn’t matter if you’re shooting with 230gr ball – Winchester, Monarch brass & steel, Federal etc.

Possible Reasons

It is a gen 4 problem. There’s an issue with the ejector in these ones.

Additionally, the extractor may not hold the case to the breech face.

The Fix

The new Glock 21 Gen 5 with the breach face cut seems to have fixed the problem.

Otherwise, replacing the ejector of the Gen 4 with the one from a 40-cal Glock can fix it. The new springs may need some breaking in.

You can also try replacing the extractor with a stainless Lone Wolf extractor. Additionally, you should also try hotter ammo with this one!

Failure to Feed Issue

Failure to feed (FTF) from Winchester PDX1s, Federal HSTs, and Hornady Critical Duty is common.

Every other bullet crashes/nose dives into the magazines or is stuck beneath the barrel’s ramp.

Possible Reasons

Two causes are more likely to occur:

  • Holding the rifle very tightly with a very rigid hand.
  • The mag spring was unable to keep up with too much slide speed.

The Fix

With Federal HSTs, Remington Golden Sabers, and Speer Gold Dots, G21 performs admirably. More things to consider are:

  • Stronger RSA,
  • Adding weight or a counterweight to the slide or barrel,
  • A stronger magazine spring, and
  • Avoid gripping the rifle too firmly or stiffly.

It’s a balancing act with an auto pistol because you have to keep the ammunition inside the gun’s design parameters.

Or adjust those parameters for different loads, whether they are weaker or stronger.

Magazine Issues

Around the tenth round, the magazine fails to feed.

They look to be leaning back, indicating that they are not maintaining parallel alignment with the follower.

Additionally, the magazine protrudes from the gun’s bottom by about a half to a full inch.

Possible Reasons

Some of the Glock frames were a little too tightly molded, which prevented some magazines from falling free.

The Fix

Remove the slide from the frame. Put a t-shirt or other thin piece of clothing over the magazine you’re having trouble with.

Push the magazine as far into the frame as you can and leave it there overnight.

Slide Rattle Problem

More than any other Glock, the rear of the slide can be adjusted from side to side. It even frequently rattles and shakes.

Possible Reasons

There are three traditional Glock “rattles,” one of which is caused by the slide-on-frame looseness.

The contrast between wide tolerances and improperly fitting parts can be seen in that seemingly “sloppy” slide fit.

The Fix

There are tools for tightening slide rails that many 1911 gunsmiths are familiar with. It’s a quick fix that could benefit your Glock.

Not Firing Issues

The slide feels as though it wants to stick back when you rack it. Only when the trigger is not pushed does it occurs. There may be a stiffer spring.

Possible Reasons

It occurs more frequently in.45 models. The Glock 21 Gen 4 spring is firmer than usual in newly manufactured firearms.

It might also occur as a result of the “break-in” stage.

The Fix

Clean, field strip, and shoot it. Glocks truly don’t have a specific “break in” phase.

Although, like other guns, they do start to loosen up after a few hundred rounds. Clean the gen 4 spring well, lubricate it with high-quality oil, and then shoot a few hundred rounds.

There shouldn’t be any more problems. In dire circumstances, replace it with a lighter aftermarket model. But that is not recommended.

User Feedback on Glock 21 Gen 4

Regardless of good or bad experiences, users always tend to change the stock sights!

During the 2005-06 period, the G21 had skipped being a durable and reliable service-grade pistol. Yet, the G21 Gen 4 has received the seal of approval from DocGKR.

In 10mm, the 21 Gen 4 appears to shoot more smoothly and easily than the Gen 3’s. Although, it had serious dependability issues with firearms during its initial years.

This was entirely the result of a flawed magazine design. Glock acknowledged it and it took them around six months to design new magazines.

If you compare lethality to size, it is plainly “too big”—especially for carrying. On that criteria, the G19 or 23, as well as a plethora of other weapons, thoroughly beat it. There is also no denying the 21’s tremendous aesthetic appeal.

Yes! Agreed it was disappointing! But the gen4 21 soon redeemed itself and became an absolute favorite with the masses.

Top 3 Alternative Guns of Glock 21 Gen 4

Based on comparing the specs, features, practicality, and performance, I have found the 3 best alternatives to Glock 26 Gen 5. 

S&W M&P 45

You might prefer the M&P’s curved trigger to the Glock’s downward-sloping design. For a full-size, double stack 45, it works great. You may carry a full size comfortably because of these features.

Springfield XDM 45

Springfield receives the most mixed kind of reviews. Its trigger pull and control are pretty much the same as the Glock 21 gen 4.

It does have that long slide which may be an issue. However, it is an amazing substitute.

FNX 45 Tactical

They are more powerful, more precise, and have great triggers. But they are quite large.

Additionally, you are going to have many issues with this one and will almost have to change every stock part.

Frequently Asked Questions (FAQs)

What is the difference between the Glock 21 Gen 4 and SF?

The Gen 4 and the SF are the same basic size. But they have slightly different shapes around the back of the grip.

What Caused the LAPD problems with the Glock 21 Gen 4?

Sludge-induced firing pin drag and weak hits brought on by oil being poured to one or both holes accessing the firing pin channel

Can you pocket carry Glock 21 Gen 4?


Can Glock 21 gen 4 stop a bear?

Very unlikely that it will.

Does a Glock 21 have a threaded barrel?



The G21 is, in my opinion, the ideal home defense weapon. Even in +P form, the low-pressure 45 ACP 230-grain ammo is subsonic and generates less sonic energy than any other cartridge except the 38 special.

Even better, it can be suppressed!

If you compare lethality to size, it is plainly “too big”—especially for carrying. On that criteria, the G19 or 23, as well as a plethora of other weapons, got beaten by G21 Gen 4. So I suggest you go for it!

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