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Thread: Phosphate under gas block

  1. #51
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    Colt already knows exactly how much reliability goes up with a more optimal cyclic rate. Likewise, when we developed our 300 BLK guns we did a week of high speed video studying this.

    AAC barrels are nitrided, so that adds no thickness, and so we already don't have to deal with a coating layer.

    We also control the bore cross sectional area to a drawing, and likewise, a layer of chrome would raise the variation in bore dimensions.

  2. #52
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    What else has been tweaked in trying to reach the cyclic rate chosen?

    What are the ammo limitations within that ideal cyclic rate?

  3. #53
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    It is not a question of reaching the cyclic rate. That was done 20 years ago when they picked the buffer weight and gas port size.

    I am speaking of reducing cyclic rate variation. Aside from ammo, which is made by someone else, the gun maker just has to try to make the rifles as identical as possible.

    The reason Colt got an unfair deal in the 'dust' tests was that the govt picked M4s off the shelf that had cyclic rates at or below 700 rpm, and competed them against XM8s and SCARs which were specially prepared by Hk and FN for this event - no doubt with cyclic rates optimal for dust tests (higher rates).

    I have to wonder, how would M4s have done if they started at 900 rpm rather than 700 rpm? Almost certainly better.

  4. #54
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    Quote Originally Posted by rsilvers View Post

    Because you have to allow for the variation in thickness. Since the diameter change can be from 0.0004 to 0.0008, you have to "allow for" 0.0008. So if it is less than that (and it will be most of the time), then there is an increased gap.
    This is all true.

    But in the M16A1 case, the bore dimension is " hone to size after phosphate coating".

    This eliminates variation from one side.

    The .00035 allowance on the barrel is slightly less than the max, but this is OK because phos is friable(crushable).

    So the extra variation in the setup amounts to .00015", or the diff between the allowance an the min thickness.

    Thats not much considering the bore is allowed .0005" and the shaft .001".
    Black River Tactical
    BRT OPTIMUM HFCL Barrels - Hammer Forged Chrome Lined 11.5", 12.5", 14.5"
    BRT OPTIMUM Barrels - 16" MPR, 14.5" MPC, 12.5" MRC, 11.5" CQB, 9" PDW
    BRT EZTUNE Preset Gas Tubes - CAR and MID
    BRT Covert Comps 7.62, 5.56, 6X, 9mm
    BRT MarkBlue Gas Tubes - BRT EXT, EXC and PDW Lengths
    BRT MicroPin Gas Blocks - .750" & .625"
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  5. #55
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    That eliminates hole variation, but when I said the variation was on both sides, I did not mean the shaft and the hole, I meant both sides of the shaft. Since Phosphate is 0.0002 to 0.0004 per surface, that is 0.0004 to 0.0008 increase in diameter of the shaft.

  6. #56
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    Quote Originally Posted by rsilvers View Post
    AAC barrels are nitrided, so that adds no thickness, and so we already don't have to deal with a coating layer.
    Just out of curiosty, what sort of 'nitriding' are you guys using? Is this like a nickel boron nidride, or a ferritic nitrocarburizing, or something else alltogether?

  7. #57
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    Ferritic nitrocarburizing, but with a very specific process to not harm the barrels. The way it is often done terrifies me. There are very few companies I would buy a nitrided barrel from.

  8. #58
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    What is the profile of the barrels AAC will be using?

  9. #59
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    Quote Originally Posted by rsilvers View Post
    That eliminates hole variation, but when I said the variation was on both sides, I did not mean the shaft and the hole, I meant both sides of the shaft. Since Phosphate is 0.0002 to 0.0004 per surface, that is 0.0004 to 0.0008 increase in diameter of the shaft.
    Right you are.
    Black River Tactical
    BRT OPTIMUM HFCL Barrels - Hammer Forged Chrome Lined 11.5", 12.5", 14.5"
    BRT OPTIMUM Barrels - 16" MPR, 14.5" MPC, 12.5" MRC, 11.5" CQB, 9" PDW
    BRT EZTUNE Preset Gas Tubes - CAR and MID
    BRT Covert Comps 7.62, 5.56, 6X, 9mm
    BRT MarkBlue Gas Tubes - BRT EXT, EXC and PDW Lengths
    BRT MicroPin Gas Blocks - .750" & .625"
    BRT MicroTUNE Adjustable Gas Blocks
    BRT CustomTUNE Gas Ports

  10. #60
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    Quote Originally Posted by rsilvers View Post
    Ferritic nitrocarburizing, but with a very specific process to not harm the barrels. The way it is often done terrifies me. There are very few companies I would buy a nitrided barrel from.
    What's so terrifying about a thousand degree molten lava salt bath dunking?
    Black River Tactical
    BRT OPTIMUM HFCL Barrels - Hammer Forged Chrome Lined 11.5", 12.5", 14.5"
    BRT OPTIMUM Barrels - 16" MPR, 14.5" MPC, 12.5" MRC, 11.5" CQB, 9" PDW
    BRT EZTUNE Preset Gas Tubes - CAR and MID
    BRT Covert Comps 7.62, 5.56, 6X, 9mm
    BRT MarkBlue Gas Tubes - BRT EXT, EXC and PDW Lengths
    BRT MicroPin Gas Blocks - .750" & .625"
    BRT MicroTUNE Adjustable Gas Blocks
    BRT CustomTUNE Gas Ports

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