AR15 firing pin retaining pin

I have a couple bolts with solid pins. Apples to Oranges. I keep retainer pins and a few other parts, gas rings, etc. in the butt trap or pistol grip of all my ARs

The firing pin retainer is far from a normal "cotter pin". It is made from harder steel and is heat treated. Replacing it with the typical hardware store cotter pin is inviting failure.

The KNS solid pins are nice but kind of a fix for a non existing problem, use 'em if you got 'em.

It's easily bent or splayed, making it impossible to re-install.

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Yeah, if you position it in a vise and drive a chisel between the halves

It'd be pretty tough to accidentally deform this pin, as:

The firing pin retainer is far from a normal "cotter pin". It is made from harder steel and is heat treated.

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an alternative part. It's a single piece screw

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Solution looking for a problem. I have never had an issue with the standard pin. It is used because it A) has just enough tension to stay in place and B) is easily hooked for removal with a bullet tip, knife tip or other improvised tool.

The AR was designed to be easily broken down for field service without tools. I like them that way.

The orginial Colt AR-15 / M-16 pin was a solid one peice design with a flat flush fitting head.
It was prone to get stuck in the bolt carrier with fouling, and there was nothing to get hold of to get it out.
They also had breakage problems.

It was soon replaced with the cotter pin design because it was more durable and less likely to break.
And even if one leg broke, it would still function.

And the loop made it possible to pry it out with a bullet tip if thats all you had.

rc

+1 for the cotter pin. They work and they've proven to last. I have yet to hear about them having issues. IMO the solid pins are pure gimmicks, an exercise in marketing to separate the ignorant from their money.

My biggest issue was troops lossing them and trying to substitute something else. I have seen them with one "leg" broken and even those worked better than pipe cleaners or tooth picks.......

-kBob

madcratebuilder said:

The firing pin retainer is far from a normal "cotter pin". It is made from harder steel and is heat treated. Replacing it with the typical hardware store cotter pin is inviting failure.

The KNS solid pins are nice but kind of a fix for a non existing problem, use 'em if you got 'em.

Click to expand...

This is accurate.

Never had an issue with a firing pin retaining pin.

No idea how one can become bent or splayed unless the person doesn't know what they are doing.

I would never use a hardware store cotter pin as a replacement.

It's easily bent or splayed, making it impossible to re-install.

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New ones are frequently "pre-splayed" and can be impossible to install unless you know the trick.

1. get two pair of pliers.
2. grab the loop-end with one pair
3. grab the legs-end with the second pair
4. twist the legs-end until the legs are no longer perfectly opposite each other
5. bend each respective leg inward SLIGHTLY
6. use the pliers to re-align the legs so they are again opposite each other.

The pin will no longer be splayed at the ends of the legs.
The ends of the legs should now come together as a point, and will guide easily into the bolt carrier.

If the ends of the legs have sharp angles, the angles can be reduced so that the ends of the legs don't "dig" into the carrier as the pin is being installed.

Replace the pin every so often, especially on carbine-length guns, as the pins tend to get pretty chewed up with extended use.

There is pretty much no financial reason not to have TWO LIFETIMES supply of replacement cotter pins. Buy a dozen or more, and un-splay them all, and then distribute them in your shooting gear so that you are never far from a ready replacement part.

New ones are frequently "pre-splayed" and can be impossible to install unless you know the trick.

1. get two pair of pliers.
2. grab the loop-end with one pair
3. grab the legs-end with the second pair
4. twist the legs-end until the legs are no longer perfectly opposite each other
5. bend each respective leg inward SLIGHTLY
6. use the pliers to re-align the legs so they are again opposite each other.

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Or just squeeze and twist while installing; I've never seen a carrier that wasn't chamfered to aid in pin installation.

Half a lifetime of automotive repair makes one very adept at getting one metal part to fit into another, though-even if alignment is less than perfect.

If you run any kind of shiny carrier, the solid pins make for a cleaner looking carrier assembly.
Since these solid pins are chromed, they tend to stick LESS when fouled than the cotter style retainers.
They are easily removed with the help of a 3/32" punch and any saavy AR15/M16 shooter will have one in his kit.
Cotter style retainer pins were introduced simply as a cost saving measure.
These pins function no better or worse than the earlier solid style pins.

Onmilo said:

If you run any kind of shiny carrier, the solid pins make for a cleaner looking carrier assembly.

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If appearance counts. My NiB BCG installed in the upper you can see the tip of the pin legs, a black dot in a sea of silver.

Since these solid pins are chromed, they tend to stick LESS when fouled than the cotter style retainers

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They better not stick, there's no way to pry them out with out tools.

They are easily removed with the help of a 3/32" punch and any savvy AR15/M16 shooter will have one in his kit.

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You always have a bullet and that's all that's needed for the standard retainer pin. The tip of the 5.56 round is the AR dismissible tool. Drives out take down pin, FP retainer pin, trigger guard, and adjusts the front sight post.

Cotter style retainer pins were introduced simply as a cost saving measure.
These pins function no bette or worse than the earlier solid style pins.

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The original solid pin was replaced because it had problems. RC nailed it when he said.

It was soon replaced with the cotter pin design because it was more durable and less likely to break.
And even if one leg broke, it would still function.

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I will add that I have never seen a stock FP retaining pin damaged or broken because of its design. This is after performing countless prefire inspections on M16s. The pins that were replaced were due to operator shenanigans, usually loosing them.

I have seen photos of bent/mangled pins, but these were from the notched hammer and open carrier designs. The disconnector didn't hold the hammer back during cycling and the hammer caught the firing pin to prevent a runaway gun. The resulting damage to the FP retaining pin was not a reflection of poor design with that part.

I met my first M16 back in 1969 and never had a problem with the "As issued" weapon. Our unit didn't have an armorer as such but we did have a bunch of spare parts on hand. Several little baggies of firing pin retainers were in there I remember. I remember losing one when cleaning my weapon out on the trail but never replaced a damaged one.

Depends on the AR and the manufacture; some are easier than others while some I hate it everything I do a complete break down for cleaning. As other's have said this is one of those parts that's good to have some around just in case.