The general belief that anti-rotate pins are only necessary if you have weak hammer springs is a myth.
The misconception in the AR world is that the walking of the trigger pin is typically caused by weak hammer springs. Many believe that, as a hammer spring ages and weakens it may no longer exert enough force on the trigger pin to stay in the groove. If it gets out of the groove at all, the rotational forces of the trigger spring can push the pin out.
Hammer pins occasionally break because the hammer spring is new/heavy and the pin steel is weak for whatever reason at the center groove.
However, inconsistencies in manufacturing and materials used can also lead to walking. An out of round hole can show up after 500 rounds on a new firearm.
Anti-rotation pins not only solve pins falling out/walking, but also allows for proper disconnector operation (so you don’t get an off-axis sear and wind up with a full-auto condition), better trigger feel, and more.
This allows keeps everything on axis, keeping the lubrication where it needs to be.
KNS Precision is well-known for making anti-rotation pins. Here’s what they had to say:
I will begin this explanation with a little back ground on this part. We are all machine gunners here at KNS Precision, Inc. and the idea was to come up with a product that would help preserve the $10K-$15K transferable M16s. We recognized a problem with the M16 in that each time the trigger is pulled or the hammer moves back and forth, that the steel pins rotate inside the aluminum receiver. We realized that stopping that rotation would stop the wear. There are “EXPERTS” out there who say that this does not happen and it is a hoax. All one has to do is to use a marking pin and mark the trigger and hammer pins and the receiver. No need to actually shoot the weapon, just cycle it and pull the trigger. You will see the rotation. If you are familiar with M60 Joe, he does a lot of work on M16s and he can verify that this is a legitimate issue. The Gun Store in Las Vegas can also verify that the rotation is an issue.
To the next question that comes up. Okay, we understand the use on an M16, but why would someone want to use it on an AR15? At one time I asked the same question myself, but after one range experience with a brand new factory rifle (very reputable company) having the pins walk out on the first magazine and the mess that cause inside the rifle, I understood why. There are three reasons why pins walk on an AR15. 1.) Improper Installation of the pins/springs 2.) Oversized/ Out of spec holes in the receiver 3.) Use and abuse wear of the receiver from the pins rotating We have had multiple customers contact us with all of the above issues. Our product eliminates concern with all of the above. I have heard people say that it is the best insurance you can buy for $33.00 . A side effect that was brought to our attention by several gunsmiths is that our Non-Rotate Trigger and Hammer Pins improves the trigger on the AR15 rifles, especially when used with match triggers. What we have found is that by locking the trigger and hammer pins together using the Non-Rotates, it eliminates the slop in the trigger.
I hope that this might help you. If you have any further questions, don’t hesitate to get in touch with me and if I can not answer it for you, I can forward it to someone who can. Thanks!
KNS Precision, Inc
112 Marschall Creek Rd
Fredericksburg, TX 78624
The lower parts kit for an AR-15 usually contains all of the pins/detents and springs necessary to complete the lower receiver.
Some lower parts kits will omit the fire control, safety, and pistol grip – or may exchange/upgrade these items for better-than-mil-spec quality parts.
Traditionally, a complete lower parts kit contains:
- Bolt Catch,
- Bolt Catch Plunger,
- Bolt Catch Roll Pin,
- Bolt Catch Spring,
- Buffer Retainer,
- Buffer Retainer Spring,
- Disconnect Spring,
- Hammer Pin,
- Hammer Spring,
- Magazine Catch,
- Magazine Catch Button,
- Magazine Catch Spring,
- Pistol Grip (A2 style),
- Pistol Grip Lock Washer,
- Pistol Grip Screw,
- Pivot Pin,
- Pivot Pin Detent,
- Pivot Pin Detent Spring,
- Selector Detent,
- Selector Detent Spring,
- Takedown Pin,
- Takedown Pin Detent,
- Takedown Pin Detent Spring,
- Trigger Guard,
- Trigger Guard Roll Pin,
- Trigger Pin,
- Trigger Spring
The Takedown Pin is located at the rear of the lower receiver, near the buffer tube, and assists the pivot pin in securing the upper and lower receivers together.
Once removed, the takedown pin allows the upper receiver to pivot on the front pin, while exposing the interior parts of the AR-15.