Ask Foghorn: What is Short Stroking?

A reader writes:

Could someone like CUJO please define for me the phrase “short stroking?” Does it have anything to do with shotguns?

Unlike the Urban Definition version of this phrase, “short stroking” a firearm is a serious malfunction with a number of causes. Luckily, I’ve had some recent firsthand experience diagnosing and fixing this issue, so let’s jump right in.

While there is a system of firearms operation called “Short Stroke” that usually involves a piston of some sort, we’re going to be using the other usage of this term. In this context, the term “Short Stroke” is defined (thanks to Nate) as “an attempt to cycle the action of a firearm (any firearm; rifle, pistol or shotgun) with a loaded magazine that fails complete the full mechanical cycle of the action, resulting in a failure to chamber the next round in the magazine and/or a failure to reset the fire control group, resulting in a failure to fire.” Confused? Let’s break it down.

Every firearm has a “Cycle of Operation” which is pretty much standard these days. That cycle of operations is generally the same for all firearms, even shotguns and bolt action rifles, and looks something like this:

The chart really could be simplified into three steps:

  1. Gun fires
  2. Fired brass is removed
  3. New round is chambered

In semi-automatic firearms, these steps happen within a split second without any user interaction (other than pulling the trigger). On bolt action rifles or pump action shotguns, the shooter would need to perform all of these activities (by working the bolt or pumping the pump) to remove the old brass and put a new round in the chamber. The following video shows an AR-15 properly following the cycle of operation — you can watch the bolt eject the spent round, strip the new round off the magazine, and lock up again to fire:

Go back and re-read my definition. Short stroking is an attempt to cycle the action—which ultimately fails for one reason or another — that results in a firearm that either has an empty chamber or a spent round in the chamber, despite having a loaded magazine inserted.

On a pistol, this would be the equivalent of slamming home a loaded magazine on a closed slide, and then only racking the slide back halfway. On an AR-15 this would be like firing an underpowered round where the bolt only moves backwards halfway, insufficient to reach the back of the magazine and pick up the next round.

The telltale signs of a short stroking firearm: even with a fully loaded magazine it will fire one round, return to battery, and then refuse to fire again. I had this issue with an ArmaLite M-15 rifle. After I fired one round, I attempted to fire the next. All I heard was the “click” of the hammer. Even worse, the bolt would sometimes get caught at the back of the magazine and fail to return to battery. Another sign specific to guns which hold the bolt open after the last round in a magazine: it fails to do so.

While the nature of the malfunction is known (the bolt doesn’t travel far enough back to eject the last round or pick up a new one), the causes are numerous. I would be remiss in my duties as resident know-it-all if I didn’t go over those as well.

1. Insufficient Rearward Force

For the bolt to move backwards, something has to move it. In a pump action shotgun, that’s the shooter yanking on the pump. In a bolt action rifle, that’s the shooter working the bolt. In a semi-automatic firearm the recoil or the gasses from the burning gunpowder do all the work.

A semi-auto firearm will short stroke due to insufficient rearward force for one of two reasons. Either there isn’t enough force to do it, or the gun isn’t capturing that force properly.

How much force there is available to the system depends on two factors: the amount of gunpowder in the round and the weight of the bullet. If either of these factors are out of balance then the round is considered “light.” It may not properly cycle the action. “Low recoil” ammunition is particularly prone to this problem; as the cartridges are loaded to reduce the force available to the gun (the force or “recoil” you feel). In recoil operated firearms, lighter recoil ammo will practically guarantee short stroking.

With gas or piston-operated firearms (like the AR-15 or AK-47 respectively), the expanding gases from the burning gunpowder needs to be properly captured to cycle the action.

In an AR-15, failure to cycle (short stroking) could indicate that either too much gas is leaking out of the gas tube, or the gas rings on the bolt aren’t creating the much needed seal. In an AK-47, the gas port in the barrel may be blocked or the gas tube could be missing some large chunks. Either way, there would be so much gas leaking out of the system that there wouldn’t be enough pressure to move the moving bits about.

2. Improper Maintenance

If the proper bits have enough force to operate the action, then there must be some force impeding their ability to function. The most common force is friction, which acts against the movement of the bolt and keeps it from cycling all the way to the rear. This friction could be caused by a buildup of dirt and grime on the operating surfaces, a lack of proper lubrication, or even poorly made parts.

3. User Error

I learned a valuable lesson in my years in the trenches as tech support: if there’s a problem with the computer, suspect the user first.

For bolt action or other such guns where the shooter has to cycle the action between every shot, it’s always possible that the shooter won’t do it right. In my early days of shooting, there were a couple instances where I would open the bolt just far enough to extract and eject the old casing but not far enough to pick up the new round. The exact same thing can happen with pump action or lever action rifles and shotguns.

What’s the fix? As my instructor said, “work that thing with AUTHORITY!” Strong, deliberate movements with the bolt ensure that you cycle it properly every time.

TL;DR: Short Stroking is an attempt to cycle the action of a firearm (any firearm; rifle, pistol or shotgun) with a loaded magazine that fails complete the full mechanical cycle of the action, resulting in a failure to chamber the next round in the magazine and/or a failure to reset the fire control group, resulting in a failure to fire.

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