Glock Gen 3 vs Glock Gen 4 Interchangeable Parts Guide (Upper & Lower Compatibility)
Glock Gen 3 and Glock Gen 4 pistols are two of the most common generations on the market and are especially popular for maintenance, upgrades, and aftermarket builds. One big reason they remain so widely used is because many parts between Gen 3 and Gen 4 are interchangeable.
That said, Gen 4 introduced a few major design changes compared to Gen 3. These updates improved certain features, but they also created several parts that are not cross-compatible. This guide breaks down what parts can be swapped between Glock Gen 3 and Gen 4, what parts cannot, and what to double-check before buying parts.
Compatibility Comes Down to Generation and Model
When people ask whether parts are interchangeable between Glock Gen 3 and Gen 4, they are usually talking about “generation compatibility.” However, even if a part works across Gen 3 and Gen 4, it still needs to match the correct Glock model and caliber.
The easiest way to think about it is:
Generation + Model + Caliber = Correct Fitment
For example, a Glock 19 Gen 3 barrel can fit a Glock 19 Gen 4 because it is the same model and caliber. But that same barrel will not fit a Glock 17 Gen 4 because the slide length is different. In most cases, parts compatibility is best when you stay within the same family, such as Glock 17 to Glock 17 or Glock 19 to Glock 19.
Upper Components (Slides, Barrels, Recoil System, Slide Internals)
Upper components include the slide, barrel, recoil spring assembly, sights, and internal slide parts. Overall, Glock Gen 3 and Gen 4 share strong compatibility for many internal slide components. The main exception is the recoil system, which is one of the biggest mechanical differences between these two generations.
Compatible Upper Components (YES)
Barrel (must match model and caliber)
Striker (firing pin)
Striker spring
Striker spring cups
Firing pin safety plunger
Firing pin safety spring
Extractor (model and caliber dependent)
Extractor depressor plunger
Extractor depressor plunger spring
Iron sights (front and rear; commonly Gen 1–4 compatible)
Not Compatible Upper Components (NO)
Recoil spring assemblies (Gen 3 and Gen 4 use different systems)
Gen 4 dual recoil spring assembly installed into a Gen 3 setup
Gen 3 recoil spring assembly used in a Gen 4 setup without proper conversion
Upper Fitment Notes (Important)
Slides may be interchangeable between Gen 3 and Gen 4 if the model and caliber match, but the recoil spring setup must be correct. Gen 3 pistols use a single recoil spring assembly, while Gen 4 pistols use a dual recoil spring assembly. Mixing slides and frames without the correct recoil system can cause function issues and reliability problems.
Lower Components (Frame Internals, Trigger System, Controls)
Lower components include the frame internals, trigger system, pins, and frame controls. Many lower parts between Gen 3 and Gen 4 are interchangeable, but there are a few parts that must stay generation-specific due to differences in the frame design.
Compatible Lower Components (YES)
Trigger bar (generally compatible, model specific)
Connector
Trigger spring
Slide stop lever
Slide lock
Slide lock spring
Frame pins (model specific)
Locking block (model specific)
Not Compatible Lower Components (NO)
Trigger housing (must match frame generation)
Magazine catch / magazine release (Gen 4 design is different)
Complete Gen 3 lower parts kits used in Gen 4 frames
Complete Gen 4 lower parts kits used in Gen 3 frames
Lower Fitment Notes (Important)
Gen 4 introduced a reversible magazine release, which is one of the biggest reasons certain lower parts do not swap cleanly between generations. Because of this, the magazine catch is generation-specific. Gen 4 frames also have slight internal geometry differences, which is why the trigger housing needs to match the correct generation of frame.
Magazine Compatibility: Gen 3 vs Gen 4
Magazine compatibility is mostly straightforward between Gen 3 and Gen 4, but it depends on how the magazine release is configured.
Compatible (YES)
Gen 4 magazines will work in Gen 3 pistols
Conditional Compatibility (Depends)
Gen 3 magazines may work in Gen 4 pistols only if the magazine release remains on the left side
Gen 3 magazines typically have a single notch. Gen 4 magazines have notches on both sides to support the reversible magazine release system.
Quick Summary: What’s Compatible and What’s Not
Glock Gen 3 and Gen 4 pistols share compatibility across many internal components, especially in the slide internals and several trigger-related parts. However, the recoil spring assembly system, trigger housing, and magazine release components are not interchangeable between generations.
For best results, always confirm the part matches your exact Glock model and caliber before installing or purchasing.
Frequently Asked Questions (FAQ)
Can I use Gen 4 parts in a Gen 3 Glock?
Yes, many internal parts are interchangeable. However, recoil spring assemblies, trigger housings, and magazine catches should match the correct generation.
Can I use a Gen 4 slide on a Gen 3 frame?
Sometimes yes, as long as the model and caliber match. The recoil spring system must be properly matched to avoid reliability issues.
Are Gen 3 and Gen 4 barrels interchangeable?
Yes, barrels are interchangeable when they match the correct model and caliber, such as Glock 19 Gen 3 to Glock 19 Gen 4.
Is this compatibility only for Glock 17 and Glock 19?
No. Gen 3 vs Gen 4 compatibility applies to many Glock models. However, parts must still match the correct model family and caliber.
Are Gen 3 and Gen 4 recoil springs interchangeable?
No. Gen 3 uses a single recoil spring system while Gen 4 uses a dual recoil spring system.