Premature Slide Lock: Potential Issues & Answers

posted on May 30, 2019

While having purchased my first 1911-style pistol and learned the handling and shooting fundamentals, I am experiencing an unusual malfunction. The slide locks back periodically before the magazine is empty, which requires depressing the slide stop to continue firing. I am using factory 230-grain FMJ ammunition I purchased when I acquired the pistol. The magazine that came with the gun is the only one I have, for now. Should I change ammunition, buy another magazine, send the pistol in for service or is there something I’m missing, which might be causing this problem? Thank you in advance for your help.

Conway Lu
Bakersfield, CA

This is a fairly unusual phenomenon in a 1911-style or any single-stack pistol magazine.

Not being able to see you shoot the pistol leaves me with a few suggestions that come to mind since I have seen this in my past experience teaching and coaching.

Most often the problem stems from the way the shooter is gripping the gun. What this comes from is movement of the gun in the shooter’s hands as it’s being fired, allowing a finger or thumb of one hand or the other to contact the slide stop, causing upward pressure as the slide is cycling. This in turn causes the slide stop to engage the arresting notch on the bottom of the slide, which locks the slide open as you described.

First, I would try tightening your grip on the pistol a bit, ensuring the grip pressure is consistent through the full magazine. Second, I would try shooting the gun with the other hand just to see if the problem still occurs. This way, the problem can be isolated as to whether it is your shooting technique or perhaps a mechanical problem.

If the problem persists, I would try a new or different magazine. If you have a friend with a 1911 that functions properly, try one or two of their magazines to determine if it is a magazine problem. With the wide variety of 1911 brands and magazines that are made for these pistols it is possible for the magazine to be a poor fit, which may contribute to the problem. The magazine should be a snug fit, but drop free when empty.

A weak magazine spring could cause this problem as well. When the gun fires, the ammunition wants to remain stationary in the stack causing downward pressure on the magazine spring as the muzzle rises. If the spring isn’t strong enough to hold the ammunition against the feed lips at the top of the magazine during recoil, the ammunition is free to bounce around momentarily, inadvertently coming in contact with the slide stop causing it to engage the arresting notch and locking the slide to the rear.

This type of stoppage usually takes place in the middle or latter part of shooting a full magazine—when there is enough weight from the ammunition and space left from the previously expended ammunition to facilitate movement and compression of the magazine spring. This allows the top rounds to float in the magazine until the spring overcomes the inertia and forces the ammo back into position.

There are two areas of the slide stop that could be contributing factors. Although rare, the slide stop could have been incorrectly manufactured with a little too much material on the tab, which is engaged after the last shot is fired by the magazine follower to lift the stop into the arresting notch, locking the slide to the rear. This excess material may come in contact with the ammunition as it advances in the magazine, which will lock the slide open prematurely if the timing is right.

Another point of consideration is the interface between the slide stop and the slide-stop plunger. Pressure from the plunger is designed to hold the slide stop in the lowered position until it is pushed up by digital pressure or the follower of an empty magazine. Insufficient pressure on the slide stop from the slide-stop plunger would allow the slide stop to move freely, randomly locking the slide open during shooting.

Try my suggestions in the order listed without exceeding your mechanical understanding of how the pistol works. If you reach a point where success hasn’t been realized to your satisfaction, send the gun back to the manufacturer for repair.


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