It’s the thumb button from what people trained on 1911s or other classic firearms tend to call a “slide release” and what Glock insists on calling a “slide stop.”
Why does Glock call it a “stop” and not a “release”? You’re looking at the reason. The cheap stamped part is not designed or manufactured to take the load of being used to release the slide. Official and canonical Glock practice is that you close the slide on a fresh mag by pulling it to the rear and letting it go — like a Luger or P.38, not guns that have Browning’s handy slide release.
Of course, the slide release of a 1911 or BHP is machined from steel billet and heat-treated appropriately. JMB Himself intended you to mash your opposable thumb down on it to close the slide, because you needed your left hand to manage the reins of your cavalry mount anyway!
This image comes from Kyle Defoor’s Instagram, where he says:
Seeing some military and LE Glock 19 Gen 4 slide stop levers breaking more than a few times. Never seen this before so often.
A lot of his commenters are… well, we’re not willing to trade commenters with him, let’s just say that. But one of them had this observation, which gibes with what we’ve heard about Glock training.
I’m a factory certified Glock armorer and at my last recert they discussed their position that the slide stop is not a slide release and using it in this fashion can, over time, lead to failures.
And couple more had the sensible comments that,
If not a slide release why the ridges on face for grip?
It seems to me that it would get more abuse from going into slide lock than slipping out of the notch to send the slide foreword again. What am I missing?
To which the Glock armorer guy replied:
[T]hat’s a valid point and an acute observation. I am remiss in failing to ask my Glock rep, who was in my office just yesterday, for clarification on this.
OK, let us offer our own opinion (note, opinion) on this.
- In our opinion, the “don’t use it as a slide release” is a retrospective position that was created by the Glock organization ex post facto when someone broke a slide release. But the oldest official Glock documents we have on hand (a January, 1992 armorer’s manual, and a Glock G1 exploded view dated 1991) already refer to the part as a “slide stop lever.” (The part owners often call a “takedown catch” is, officially, a “slide lock,” not to be confused with the slide stop lever).
- Re: “why the ridges on face for grip?” On p. 14 of the 1992 armorer’s manual, it describes how to lock the slide back, and includes a picture. “[L]ock the slide open by pushing up on the slide stop lever while pulling the slide to the rear with the non-shooting hand.” (It then tells you to “Pull back slide to release slide stop lever and close action.” But it doesn’t warn you not to use the slide stop lever to release the slide).
- “Why does it break?” OK, here’s a couple pictures of Glock slide stops. First, here’s an OEM slide stop, photographed from the inside. Now, we didn’t have a handy photo of this from the outside, but this photo of a Vickers Tactical extended slide stop (we’ve got this part on our own Glock) shows what the other side looks like. Compare this to the failed stop at the top of this post.
We now have several clues as to why the stops are failing.
- People continue doing something the manufacturer says not to do.
- The slide stop is made from a single piece of sheet metal, stamped (“pressed” for Europeans) and folded to net shape.
- There is a small rounded notch, adjacent to the part of the stop that folds over to the inside, right where the part Kyle photographed began to fail (see where the failure crack is kind of gray at the top? That’s the oldest part of the failure. When it weakened the slide stop enough, the rest failed all at once — that’s the shiny part of the crack). The reason for the notch is to prevent a “stress riser” from causing the part to begin failing at this point, and it obviously is not working in 100% of use conditions.
- And that the problem just started showing up with greater frequency, suggests that some aspect of the manufacturing of the part may have been changed recently. Manufacturers are always making small changes in parts to improve something about them (often something that matters to the manufacture, like lower cost, or increase speed of manufacture, and doesn’t matter quite as directly to customers). Manufacturers also are known for making parts in-house and outsourcing other parts to subcontractors. These subs can change at any time.
- Putting thumb pressure on the slide stop stresses it several different ways. It can load it in torsion (twist), for which the engineers probably didn’t do the math on this part. It will definitely bend the part laterally (per the gun’s orientation). That stresses the outboard (left) side of the slide stop in tension, and the inboard (right) side in compression. Another way to think about it is when you bend a plate or bar, the side bent convex is loaded in tension, and the side bent concave is loaded in compression. Our best guess (and based on one picture of one part, it can be no more than a guess) is that this part began to fail from tension at the upper outboard corner of the slide stop.
- It’s a trivial physics or engineering problem to calculate the stresses on the part, but to know whether they exceeded the design strength of the part, we’d need to know the exact materials and heat-treating condition of the part.
A question on the Instagram page about whether this is happening primarily in high round-count guns isn’t answered, but round count doesn’t necessarily load the slide stop. A lot of cop guns are seldom fired, but are loaded and cleared at least once every shift. If they’re thumbing the slide stop a lot, they can bust their slide stop without even firing a shot.
One last thing: the failure of this actuating button end of the slide stop makes it impossible (or very difficult, requiring tools) to lock the slide back without an empty mag in the pistol. However, without the end of the stop, it looks to us like the basic running of the gun would still be OK, until you needed the slide stop to handle a malfunction. So in combat terms, this failure of the slide stop is fail safe.