The topic of anti-rotation / anti-walk pins comes up now and then. We used to link an article written by a third party, it's been removed and replaced by our shorter version.
For the record, we're against them. They're unnecessary for properly designed and made triggers. The trigger should have a J spring that rides on the middle groove of the trigger/hammer pin and prevents the pin from walking, and the trigger pin is held by one or both of the hammer spring "legs". If your triggers require them, our advice is to use a properly designed trigger that can hold the trigger and hammer pins without needing external help in the form of screws and anti-walk/anti-rotation pins, AR15 and M16 triggers and hammers should not need them.
Below picture shows a Schmid Tool semi auto hammer, with the J spring visible through the hammer pin hole. The J spring engages the middle groove on the hammer/trigger pin and prevents it from walking, but doesn't stop it from rotating.
The same Schmid Tools semi auto hammer with its springs resting on the grooves of our HTP (hammer, trigger pin). HTP has three grooves, TDP hammer and trigger pins have two grooves. One spring leg engaging the groove is sufficient to keep the trigger pin from walking, and like the J spring in the hammer, it doesn't stop the trigger pin from rotating, nor is it necessary to do so.
With few exceptions, M16s from the Vietnam war era in US military service never needed them. These weapons have seen far more use and go through many users than most of the AR15s and M16s in civilian hands, that alone should be evidence enough. Properly designed and made triggers don't need anti-walk pins, nor do they benefit from them.
