A Trigger Pin that vibrates out of the lower receiver during firing, is often times referred to as a “Walking Trigger Pin”. “Walking Trigger Pins” are usually the result of two common mistakes made by those new to assembling their own lower receivers involving installation of the FCG (Fire Control Group).



Problem Number One: Hammer Spring Leg Placement

Often times the assembler mistakenly places the legs of the hammer spring under the trigger pin, against the bottom of the FCG pocket of the lower receiver along the sides of the trigger assembly. Taking a look at the diagram below, we see that the hammer spring legs actually ride on top of the trigger pin.

The pins utilized for the trigger and hammer, are designed with two circumferential grooves, one groove outboard and one center. When a pin is utilized in the trigger position, it is retained within the lower receiver by the tension of one of the hammer spring legs riding within the outermost groove of the pin. (See View A of the illustration below.)

If the hammer spring legs are not placed on top of the trigger pin, with one leg placed in the outermost trigger pin groove, the firer may experience a “Walking Trigger Pin”.



Problem Number Two: Incorrect Hammer Spring Installation

Occasionally lower receiver parts kits (LPK) arrive with the hammer and hammer spring separated from each other. If not following the maintenance manual, or detailed assembly instructions, incorrect installation of the hammer spring by the assembler is often times the result. Or, there was a mistake during assembly of the two by the distributor or Mfr., resulting in incorrect installation of the hammer spring.

Taking a look at the illustration below (Position Of The Hammer Spring Legs), we see the correct installation of the hammer spring on the hammer itself. Incorrect installation of the hammer spring on the hammer, can lead to incorrect pressure applied to the trigger pin by the tails of the hammer spring, most critical being the spring tail riding in the trigger pin groove.

This lack of proper spring tail pressure, can often times lead to a “Walking Trigger Pin”.


A not too common problem, but one which I have personally experienced which can lead to a “Walking Trigger Pin”, was caused by the grooves not being cut deep enough in the trigger pin to sufficiently hold the tail of the hammer spring.

In this instance, I had to resort to opening up of the groove, using a small jewelers rat tail file. This was a temporary fix. Removal and replacement of the trigger pin with an in-spec trigger pin would be highly recommended.