AK trigger slap, doubling - fix

[PA Rifleman]

I've been mulling this for a few days, hope I didn't leave anything out. Had a misbehaving SAR that I straightened out, thought I'd share my experiences here. To keep this balanced, there are online vendors that sell trigger kits for those so inclined.

First, a few caveats:

• This information is provided for your enlightenment. Any modifications you perform, you do so at your own risk.
• The images shown here are drawn for relational interaction, and not drawn to exact scale. I have not attempted to replicate exact scale due to the large variations in AK dimensions.

All images enlarge with a mouseclick.



Trigger slap is the sensation of the trigger rebounding or "slapping" the shooter's trigger finger during firing. The sensation is a sharp, abrupt forward jolt from the trigger when the rifle discharges. It can be consistent with every shot or intermittent, sometimes favoring one type of ammunition. For this reason, it's easy to misdiagnose this as an ammunition problem.

Trigger slap occurs when there's insufficient clearance between the hammer, trigger and the disconnector. When this happens, the force of the resetting hammer is transferred into the trigger through the disconnector, causing the trigger to abruptly "slap" forward.

Doubling is when the rifle fires more than one shot with a single pull of the trigger, and the rifle is not equipped for full auto fire. Sometimes the shooter may discover the hammer resting on the firing pin (released or fired position) on a loaded chamber. Pulling the bolt carrier back far enough to reset the hammer will often result in a successful discharge.

All of these common symptoms are caused by a minor defect in the disconnector, located in the fire control group (FCG). Fortunately it's often the result of too much material, so removing the excess will usually correct the problem.

First, we'll explore why the problems are occurring, and then we'll cover how too fix it without replacing a bunch of parts.



(See diagram) The disconnector rides on the same shaft as the trigger and is spring loaded forward. It acts like a see-saw and tilts forward until the forward pad rests on the trigger casting. Note that all points on the disconnector will execute a radial path around the trigger pivot pin (common axis). This will become important later.

During firing, the hammer retreats in a circular path back toward the trigger. Since the trigger has already been pulled and cannot retain the hammer, the disconnector secures the hammer until the trigger is released. During the process of securing the hammer, the hammer presses the disconnector back against disconnector spring pressure. The hammer overcomes the disconnector and spring, and the disconnector snaps back into position after the hammer passes, capturing the hammer.

When the shooter releases the trigger, the disconnector releases the hammer, and the trigger’s hammer hook now controls the hammer.


The aperture or opening gap between the disconnector and trigger hook must be slightly smaller than the hammer’s arresting pads. If not, the disconnector or trigger will fail to catch the hammer resulting in doubling, or a released hammer on a loaded chamber. In this diagram, “A” represents the aperture size and “B” represents the hammer dimension.

If the disconnector hook sits too far back, it will not consistently arrest hammer movement, allowing the hammer to ride up on the bolt during closure, or delaying the hammer briefly and subsequently releasing it before reset. This results in the doubling or dead hammer symptom, and is caused by too much material left on the forward pad of the disconnector.

With trigger slap, the disconnector isn’t able to retreat far enough back to allow the hammer to pass, so the disconnector pushes the trigger out of the way. The trigger transfers this motion into the shooter’s finger, creating the sensation of “slap”.



Fixing doubling:
You can correct this by replacing the disconnector, or by removing a small amount of material from the forward disconnector pad. The least amount of material removal that produces satisfactory performance is the correct amount. And, don't be seduced by the "more is better" philosophy. If a little's good, more isn't better. Don't take off more than necessary, or the disconnector hook may rest too far forward and actually try to block the hammer. If this happens, you'll need a new disconnector hook.

The least amount of material removal that produces satisfactory performance is the correct amount.

Fixing “slap”:
If there's too much material on the rear disconnector pad, it will lack adequate clearance between the bolt carrier, disconnector and trigger. This results in a chain collision between the bolt carrier, disconnector and the trigger. The energy is then transferred into the shooter's finger, producing the "slap" sensation. This can be corrected by removing just enough material on the rear of the disconnector near the spring well. Remove only enough to allow proper clearance, no more.

In the next diagram, note the colors. Blue is the area where you want to remove a small amount of material to correct doubling, and removing material from the red area helps correct trigger slap.



Typical Kalashnikov disconnectors (images taken from various internet sources)



UPDATE 16 July 2007: test fired aforementioned AK at length at the range, worked like a champ. No doubling, no slap.