Anti-walk and anti-rotation pins?

[kymasabe]

Bought my first drop in trigger, a JMT Saber, and I'm pretty sure it comes with pins, and I understand the idea behind anti-walk pins, but not sure I understand what anti-rotation pins are for?

[JohnKSa]

They're designed so that the pin itself won't rotate in the hole.

It's fairly common for a pin to retain a part that is intended to pivot on the pin. If the pin is loose in the hole and is tight on the part, the pin could pivot in its hole instead of the part pivoting on the pin.

The only real reason I can see for anti-pivot pins would be if the part and the pin are hardened steel but the pin is going through something much softer. Say through an aluminum receiver. So the part pivoting on the pin (assuming sufficient lubrication) wouldn't really cause any wear (and if it did, the pin or part could be fairly easily replaced) while the pin pivoting in the hole through the softer material might cause wear to that part that could eventually become problematic.

I should point out that I haven't done any real research on this topic so this should be considered to be more of an opinion than established fact.

[rickyrick]

Not sure if it is a common issue or not.
I have one lower that I’ve installed a cassette type trigger and it came with the anti-walk/rotation pin kit for free so I used it.

Someone somewhere must’ve had an issue.
The cassette style triggers put different forces on the pins as compared to the regular type triggers. That is all I know.

[kymasabe]

JohnKSa....great explanation, thank you.

[BornFighting88]

I picked up a set of “Anti-Squirrel” pins a few years ago for my AR lower that I swap uppers on for different uses. It was the best purchase I made. The pins all had grooves in them for the respective spring arms to seat in, specifically the hammer torsion spring and the trigger return spring. These specific pins had threaded holes in the ends for cap screws. Low profile heads and hex drive to make it just near impossible to slip out of the head.

Dabbed the threads in blue loc-tite and snugged them down. They haven’t moved since. I am a fan of them. I think it put me out $25 with shipping for the set. That was right when Obama took office, and the panic set in that he would do something stupid. So they might have been a $5 with shipping set, but I was having issues with walk out at the time, and figured what the heck.

[NeverEnough]

Never had a pin walk or rotate on me. I use anti-walk/rotation pins in 80% lowers just for peace of mind

[HWS]

I installed a drop in trigger along with anti-walk pins several years ago. No problems whatsoever.

[Willie Lowman]

I have 21 years of experience with AR rifles. I have owned half a dozen and shot enough to have worn out the barrel on a Colt Hbar. I have never had a pin walk. I guess it would be very hard to tell if it was rotating but I have never seen the need for these special pins.

[44 AMP]

The original AR/M16 design kept the pins from walking with spring legs riding in grooves on the pins. Improper assembly could negate that, and I've personally seen it happen. Saw a trigger pin that had walked about half way out turn a semi auto shot into burst fire. This is the reason regular GIs were not authorized to disassemble the lower receiver group. Company Armorers were not authorized to disassemble the lower receiver group. That was a function of Direst Support level Small Arms repairmen, people who had been trained in how to put it back together, CORRECTLY. I was one of those in the 70s.

Pin rotation was never an issue, GI parts just don't fit that tightly on the pins.

Now, when you replace the GI system with aftermarket parts, you do lose the benefits of the GI system pin retention, so something else must be done to ensure the pins don't walk. Market solution: "anti-walk" pins.

[MarkCO]

Stock triggers, as 44 AMP correctly explained, don't need them. Cassette or cartridge triggers benefit from anti-walk so the pins don't fall out as there is no retainer in the cassette. Anti-rotation pins became a thing for lightweight carriers with a higher velocity where some set-ups would, over time, enlarge the holes making them looser. But, if you had anti-walk, it would be a LOT of rounds before there was an issue.

Then came PCCs, with much higher forces on the hammer and thus transferred through to the pins. Some have egged out the front pin resulting in malfunctions. The anti-rotation pins that are locked together transfer some of that force to the rear pin mitigating the wear of the front pin hole. I won't run non-connected pins in a PCC.