Bolt ID?

[Cane55]

I can’t tell what brand this bolt is and couldn’t find it searching previous posts. The seller said it’s a top quality milspec bolt. Do any of you guys recognize this bolt and who might make it? The only markings on it are the “HPT/MPI” and some number on the inside of the extractor (which has a gold/copper colored extractor spring & red/orange colored o-ring), but no company name is printed on it. If any of you guys can identify I’d greatly appreciate it. Thank you.

67279

67280

67281

[lysander]

Rust colored o-rings are usually silicone rubber. Not only a poor choice for the application, totally unnecessary with a gold/copper spring.

[MikhailBarracuda91]

That's an FN extractor. The bolt probably is too. Look more closely and see if there is a stamp on the bolt saying "MPF"

That's a really good bolt if the whole thing is FN (it probably is even if it doesn't have the stamp.) And it's more than likely a contract overrun. Maybe even M16A2

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[Curlew]

The “HPT/MPI” marking is very similar to those on some bolts I got from E2 Armory, which I understand to be a retail outlet for AO Precision. Same font, same location on the bolt, just not as bright white as yours.

Extractors are different though: mine don’t have the FN CAGE code, they have the older, silver-colored spring, and the O-rings are black.

IIRC, I’ve read that AO Precision is a supplier to FN.

[Cane55]

That's an FN extractor. The bolt probably is too. Look more closely and see if there is a stamp on the bolt saying "MPF"

That's a really good bolt if the whole thing is FN (it probably is even if it doesn't have the stamp.) And it's more than likely a contract overrun. Maybe even M16A2

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Thank you for your response and invaluable information. Your right, it’s an FN milspec M4 bolt. I didn’t realize the number on the extractor was the CAGE code. It doesn’t have the “MPF” physically engrained in the bolt but I found out from the company I purchased it from (Geissele) they don’t do that anymore. Thank you, I really appreciate your help & everyone else that responded. You guys have an incredible amount of knowledge & I am always learning from you.

[Cane55]

Rust colored o-rings are usually silicone rubber. Not only a poor choice for the application, totally unnecessary with a gold/copper spring.

That’s a great point, but I’m going to probably swap it out with a 5 coil chrome silicone Sprinco extractor spring anyway.

[prepare]

That's an FN extractor. The bolt probably is too. Look more closely and see if there is a stamp on the bolt saying "MPF"

That's a really good bolt if the whole thing is FN (it probably is even if it doesn't have the stamp.) And it's more than likely a contract overrun. Maybe even M16A2

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Those are Azimuth correct?

[MikhailBarracuda91]

Thank you for your response and invaluable information. Your right, it’s an FN milspec M4 bolt. I didn’t realize the number on the extractor was the CAGE code. It doesn’t have the “MPF” physically engrained in the bolt but I found out from the company I purchased it from (Geissele) they don’t do that anymore. Thank you, I really appreciate your help & everyone else that responded. You guys have an incredible amount of knowledge & I am always learning from you.No problem, this site always helps me out

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[MikhailBarracuda91]

Those are Azimuth correct?That sounds right, I remember reading a whole bunch about this like 5 years ago

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[Disciple]

Rust colored o-rings are usually silicone rubber. Not only a poor choice for the application, totally unnecessary with a gold/copper spring.

I already follow your advice and do not combine an o-ring with the copper spring but why is silicone a poor choice?

[MikhailBarracuda91]

Rust colored o-rings are usually silicone rubber. Not only a poor choice for the application, totally unnecessary with a gold/copper spring.I always wondered about this. I have a complete FNMI milsurp BCG and it has this exact spring and O ring setup.

Why did they continue to issue the M16A4 like this? The upper it came in was only from 2013, and it was NOS.

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[lysander]

I already follow your advice and do not combine an o-ring with the copper spring but why is silicone a poor choice?

The original band-aid o-rings were either fluoro-silicone or fluorocarbon, I forget which, but these rubbers are more resistant to oil and moisture absorbsion. Also, all the rust colored o-rings I have seen used as spring assist are softer rubbers (60 shore), which kind'a defeats the purpose.


I always wondered about this. I have a complete FNMI milsurp BCG and it has this exact spring and O ring setup.

Why did they continue to issue the M16A4 like this? The upper it came in was only from 2013, and it was NOS.

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Military issue A4s don't have the o-ring at all.

Commercial ones have it because there are a lot of uninformed people that still think the o-ring is necessary. In reality, unless you are shooting full-auto, or going with a really light buffer bolt carrier, you can probably get away with the old silver spring.

[MikhailBarracuda91]

The original band-aid o-rings were either fluoro-silicone or fluorocarbon, I forget which, but these rubbers are more resistant to oil and moisture absorbsion. Also, all the rust colored o-rings I have seen used as spring assist are softer rubbers (60 shore), which kind'a defeats the purpose.


Military issue A4s don't have the o-ring at all.

Commercial ones have it because there are a lot of uninformed people that still think the o-ring is necessary. In reality, unless you are shooting full-auto, or going with a really light buffer bolt carrier, you can probably get away with the old silver spring.I wonder if the BCG that it came with is the original one for that upper. So your saying it's probably a carrier out of an M4

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[Cane55]

Rust colored o-rings are usually silicone rubber. Not only a poor choice for the application, totally unnecessary with a gold/copper spring.

Why is it a poor choice with the gold/copper spring? Is it because the gold/copper spring is too strong and doesn’t require an o-ring? Do you feel the gold/copper spring is as good as a CS Sprinco extractor spring & as long lasting? Just wanted to know which one is better. Thanks.