Modern Cotter Pin Firing Pin Retainer vs. Traditional Solid Pin

**AR-Tenner** · 12-08-17, 13:04

Hi Folks,

I normally don't even think of straying from mil-spec with any of the parts in my ARs (except for the LMT enhanced bolt, because, let's face it, it's made by LMT). However, I am the proud owner of a 1959-production Portuguese AR-10, and through my research contacts - I am the author of the recent Collector Grade Publications book on the AR-10 - I learned that the rifle I now own has a round count through it of roughly 40,000 rounds, many in full-auto mode, and never has had a part replaced (it cost me more than I are to admit to buy a spare extractor, extractor spring, gas rings, and charging handle as spares in case I need to replace parts in the future). This has given me a profound respect for the design of the parts on this rifle. This is what pushed me to make my carriers in all my AR-15s chrome-plated, and with the LMT Enhanced Bolt has relegated my previous BCG "A-Team" of Colt Carrier/firing pin/cam pin/retaining pin and ArmaLite Bolt to the backup role.

Aside from the chrome BCG, the other main difference in parts I saw on the Portuguese AR-10 that I actually could emulate in my AR-15s was the firing pin retainer. I am not overly displeased with the standard cotter pin type used today, although I have worn out and replaced 2 in the 25,000 rounds I have put through my modern AR-10. I did notice, however, that quite a few companies are offering this part in the original solid pin with split end, just like on the early AR-15s and my Portuguese AR-10. I know the ones from KNS have mixed reviews due to the split ends breaking from installation fit problems, but I have a source that makes stainless ones, and I am seriously considering giving those a try.

Does anyone have experience or engineering insight into these, and whether they might be more durable than the standard cotter pin? Also, is there any possible downside I am potentially overlooking, like them being too stiff or hard and putting too much pressure and wear on the firing pin or carrier, for example?

Thanks for your advice

**lysander** · 12-08-17, 16:25

The change was mostly driven by economics of manufacture. The current wire-style is easier and cheaper to produce correctly.

The old-style machined pin has to be turned, then have the end cut then spring tempered. During the early "testing" of the M16, such that it was, it was found that the drastic change in material thickness lead to the prongs being either too hard and brittle, or too soft and easily bent out of shape. The new-style, being wire and of a constant thickness are easily tempered.

There is no loading of this pin, so either is more than strong enough, if made right.

**EzGoingKev** · 12-08-17, 16:39

KAC made their bolt with the solid insert. They put a roll pin in the bolt so the pin would not just pull out.

DPMS also uses the solid insert.

**AR-Tenner** · 12-08-17, 16:53

Originally Posted by EzGoingKev

KAC made their bolt with the solid insert. They put a roll pin in the bolt so the pin would not just pull out.

DPMS also uses the solid insert.

Boy, now there is a night-and-day comparison of the best quality to the worst quality in the AR game. The solid pins I am considering are stainless ones that come from a well-known source I have used before who gets them from a military contractor. I am not sure I would trust the KNS ones, and DEFINITELY would not trust the DPMS ones. Hydrogen embrittlement is a problem with such parts, and apparently DPMS does not do the proper heat-treating to ameliorate the issue.

**tom12.7** · 12-08-17, 17:31

OP, I'm curious about the source of your SS FP retainer. You can PM if you prefer.

**Cold/Bore** · 12-08-17, 18:34

Originally Posted by tom12.7

OP, I'm curious about the source of your SS FP retainer. You can PM if you prefer.

Oh do tell.

**tom12.7** · 12-08-17, 19:13

Please don't be like that, this industry isn't my bread and butter anymore, but I am curious about current events. Sometimes products are good/bad/indifferent that pass through some hands before public scrutiny. I would not want an open forum judgement that could lead to a company's future direction in this way.
At this time, X product is just that, not named.

**Cold/Bore** · 12-08-17, 19:18

Originally Posted by tom12.7

Please don't be like that, this industry isn't my bread and butter anymore, but I am curious about current events. Sometimes products are good/bad/indifferent that pass through some hands before public scrutiny. I would not want an open forum judgement that could lead to a company's future direction in this way.
At this time, X product is just that, not named.

I didn’t mean it like that. I should have responded to the OP’s message, not yours. I was curious too and was hoping he would share it openly. My apologies.