Modern Cotter Pin Firing Pin Retainer vs. Traditional Solid Pin

[EzGoingKev]

If you have a bolt with an unshrouded firing pin the keeper sees a lot more than a small load.

[StainlessSlide]

If you have a bolt with an unshrouded firing pin the keeper sees a lot more than a small load.

When, and in which direction?

[Sumppi]

When, and in which direction?

I'd venture to take a guess that the load comes from the hammer (recocking it) when the carrier cycles back.

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[EzGoingKev]

The firing pin comes in contact with the hammer during the bolts cycle. This contact pushes the firing pin against the keeper. It beats up the keeper.

My 6920 is an older model that had the half moon carrier with the unshrouded bolt carrier. After shooting a few thousand rounds through it I noticed the keeper was all beat up. I replaced it with a new one and after a few thousand rounds it was beat up too. I had never seen this on the M16 so I googled it and learned the cause.

[Sumppi]

The firing pin comes in contact with the hammer during the bolts cycle. This contact pushes the firing pin against the keeper. It beats up the keeper.

My 6920 is an older model that had the half moon carrier with the unshrouded bolt carrier. After shooting a few thousand rounds through it I noticed the keeper was all beat up. I replaced it with a new one and after a few thousand rounds it was beat up too. I had never seen this on the M16 so I googled it and learned the cause.

Kinda offtopic, but what was the point in making a carrier with unshrouded firing pin?
I do understand the reason for a half-moon carrier (as idiotic it is...)

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[EzGoingKev]

Kinda offtopic, but what was the point in making a carrier with unshrouded firing pin?

Colt did it so you could not convert the rifle to full auto. If the rifle was converted to full auto the firing pin would snap due to the high rate of contact.

[Sumppi]

Colt did it so you could not convert the rifle to full auto. If the rifle was converted to full auto the firing pin would snap due to the high rate of contact.

OMG.. Just how stupid they were(are)?
Like half-moon bolt carriers and searblocks weren't enough stupid.

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[AR-Tenner]

Yep, and unlike sear blocks and half-moon carriers, the unshrouded firing pin was actually a serious problem, putting the stress of the hammer recocking on the firing pin and not the carrier. Thus led to the smaller-diameter "semi auto" firing pin, and the need to regularly replace firing pins. That was by far the worst way in which Colt butchered the AR-15 for the civilian market. As much as I love keeping things original, I will not fire an SP1 without first dropping a modern Colt or CMT M16 BCG in it.

[EzGoingKev]

Yes, the firing pins took a beating too.

I replaced the parts in mine with an LMT FA enhanced carrier and a large shoulder firing pin.

[AR-Tenner]

Yes, the firing pins took a beating too.

I replaced the parts in mine with an LMT FA enhanced carrier and a large shoulder firing pin.

Duh, forgot that in addition to the Colt and CMT BCGs, I am a HUGE fan of the LMT Enhanced Bolt. I also am partial to ArmaLite's bolt, as it has the recessed 4th lug that balances the forces and causes the bolts to last a lot longer.