AR-15 bolt carrier material and hardening process?
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  1. #1
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    Question AR-15 bolt carrier material and hardening process?

    Trying to make an AR-15 bolt carrier and stuck on the hardening process.

    from what I can tell one approach is to start with 8620 steel, machine it, harden it, then grind to correct the deformation caused by hardening, then phosphate. From what I gather, this is the old mil-spec process.

    I want to use more modern nitriding and preferably I'd like to skip the grinding step to keep things simple. I.e. harden--->machine--> nitride.
    I'm not sure what HT process to use though. Any ideas?

    On the other hand I see 4140 steel is used for barrels and can be hardened so is there any reason not to use that for a carrier as well?

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    Quote Originally Posted by endmill71 View Post
    Trying to make an AR-15 bolt carrier and stuck on the hardening process.

    from what I can tell one approach is to start with 8620 steel, machine it, harden it, then grind to correct the deformation caused by hardening, then phosphate. From what I gather, this is the old mil-spec process.

    I want to use more modern nitriding and preferably I'd like to skip the grinding step to keep things simple. I.e. harden--->machine--> nitride.
    I'm not sure what HT process to use though. Any ideas?

    On the other hand I see 4140 steel is used for barrels and can be hardened so is there any reason not to use that for a carrier as well?
    I could be wrong on this as we have been modifying only one type of bolt carrier. But I believe typically they are made from 8620, then ferritic nitrocarburized, then black oxide coated(no remachining needed).

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    8620 will not harden without some form of surface treatment like carburization. It doesn't contain enough carbon.

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    I've had a couple salt bath nitrited-Melonite QPQ.

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    I believe bolt carriers are made from one of the carpenter steels
    Also make sure you get the hardening right. The last big scare bcg’s were being sold that were not properly hardened and did not last 500 rounds. An easy non scientific way to test if your buying one was to strike two together lightly
    They should ring and not mark each other


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