Have you had issues with AR15 trigger group pins sliding out? Here is top 3 reasons to use anti walk pins to secure the trigger group in an AR15 lower receiver.
1. Prevents Pins From Sliding Out
The first obvious reason is to prevent trigger pins from sliding out of the receiver during heavy use. Vibration and repeated recoil will sometimes push the pin out if the hammer spring isn't retaining the pin. When that happens, it will be a catastrophic failure and the trigger group will basically collapse inside the receiver without the pin holding them in place.
In addition, the tolerance of the trigger pin may not be completely fit a particular receiver tight even if most pin holes are sized 0.154" in diameter. This brings to the second reason:
2. Prevents Point Stress To Lower Receiver Trigger Pin Holes
AR-15 lower receivers are typically manufactured using 7075 T6 aluminum, a robust and lightweight material widely utilized in firearm construction.
Conversely, trigger and hammer pins are predominantly made of steel due to its durability and resistance to deformation under pressure. Steel pins, under the tension from the hammer spring, pivot within the receiver as the hammer engages the trigger. This dynamic interaction is crucial for the firing mechanism to function effectively.
Continuous friction between the steel pins and aluminum lower receiver can gradually cause wear and tear on the pin holes over time. This friction, aggravated by the pressure exerted by the hammer spring, can lead to the deformation of the receiver pin holes, and affect disconnect sear contact surface.
As the steel pin constantly grinds against the aluminum part, the round shape of the pin holes can gradually become elongated or "eggshaped." This deformation, if left unchecked, may compromise the proper alignment and functioning of the trigger mechanism.
So using anti walk pins or anti rotation pins prevents this mitigate this issue.
3. Secures Pivoting Location For Trigger and Hammer
Drop-in cassette triggers have tighter tolerances compared to standard triggers in order to effectively contain the AR15 trigger group. This ensures optimal performance in terms of trigger pull weight and reset without relying imperfection of lower receiver quality from one manufacturer to another.
The reason behind this is that not all receiver holes and triggers have the same level of tolerance. Some receivers allow users to add set screw tension to hold them securely in place.
A similar principle applies to the use of anti-walk pins, as different trigger systems may function differently depending on the receiver. To ensure that the trigger bow and hammer can pivot freely, it is highly recommended to utilize anti-walk pins.