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Thread: Gas port erosion with different barrel profiles

  1. #11
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    Quote Originally Posted by Magic_Salad0892 View Post
    This isn't true in every case. To the best of my knowledge.

    You know Andrew's 40K round test that's been passed around lately?

    The "Federal Barrel" only had 10k in it, and the gas port had showed erosion. The rifling and all is still intact. Now he didn't measure the leade, or throat (I wish he would have, and I've thought of contacting him about it.) but I'd be willing to bet that at 10k rounds it would have been mostly intact.

    Also. I do think barrel thickness makes a difference. But I don't know how measurable. And I think it'd have to be a more extreme example to measure it properly. Like SOCOM profile against LW. Not M4 profile.

    Assuming both barrels were shot using the same ammo, under similar conditions, and were made the same way, by the same maker, and of the same barrel length.
    Not saying your wrong, just never heard of it.
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  2. #12
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    I bet it's negligible... but I could see how a full profiled barrel would absorb more heat and have the potential for a slight reduction in port errosion.
    "You people have too much time on your hands." - scottryan

  3. #13
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    I've always been curious about this too.

    What wears faster?

    .625" @ gas port or .750" @ gas port?

    Assuming same ammo, rate of fire, etc...

  4. #14
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    Quote Originally Posted by samuse View Post
    I've always been curious about this too.

    What wears faster?

    .625" @ gas port or .750" @ gas port?

    Assuming same ammo, rate of fire, etc...
    Given that the gas port and gas block functional assembly is the same for each barrel profile, they should have similar erosion rates. It should be noted that not all gas ports are the same size and smaller ports should exhibit higher gas velocities and thus slightly faster erosion. Even though the material removal rates may be similar, a gov't profile barrel has a .0625" wear advantage on a pencil barrel, so it will last longer.

    There would probably be less erosion if the port was finished with a slight countersink or radius, but that would add an extra machining operation.

    -Hold the phone- are we talking erosion within the bore or at the gas block to barrel interface?
    Last edited by Krusty783; 01-14-13 at 15:56.

  5. #15
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    Quote Originally Posted by Krusty783 View Post
    Given that the gas port and gas block functional assembly is the same for each barrel profile, they should have similar erosion rates. It should be noted that not all gas ports are the same size and smaller ports should exhibit higher gas velocities and thus slightly faster erosion. Even though the material removal rates may be similar, a gov't profile barrel has a .0625" wear advantage on a pencil barrel, so it will last longer.

    There would probably be less erosion if the port was finished with a slight countersink or radius, but that would add an extra machining operation.

    -Hold the phone- are we talking erosion within the bore or at the gas block to barrel interface?
    I was talking about gas port erosion.

    Will the gas port on the heavier section (.750" OD @ FSB)of an M4 barrel be less prone to wear (given all other factors being equal) than the same gas port on a light (.625 OD @ FSB) barrel.

    Does the wall thickness matter?

  6. #16
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    I appeciate the thoughtful replies and discussion. SMT85 has me right...and I was mainly wondering about any erosion difference on the bore side of the port between .625" barrels and .750" barrels of the same length. It sounds like it should be negligible in the grand scheme, with throat erosion maybe even negating the concern at that high of a round count.

    Also, anyone know if port diameters vary between .625" and .750" barrels with the same length and port location?

    ETA: I sincerely apologize to the board and to MistWolf for my behavior...we have enough enemies lately without fighting amongst ourselves over the trivial stuff, and I'm sorry I engaged on that level.
    Last edited by ether; 01-14-13 at 23:09.

  7. #17
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    Being in the profession I Was in,,,how much erosion will cause a failure and what will erosion cause? Higher operating [bolt] pressure or will the erosion cause accuracy problems from barrel wear in the area? Guns are a machine and machines wear out and "hopefully not" break.
    Last edited by SteveS; 01-14-13 at 22:44.

  8. #18
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    SteveS - Check out the video link in this thread that Magic referred to:

    http://m4carbine.net/showthread.php?...light=40%2C000

    Although this was more indicative of a torture-test case than a long-term use case, I was pretty surprised by the visible amount of gas port erosion that these 10K barrels exhibited.

    Your question is a really good one though, if I understand it - would gas port erosion start to affect reliability before throat erosion ever would? We know throat erosion can ruin barrel accuracy, but how long will the weapon keep firing reliably until gas port erosion gets the best of it, and reliability is affected?

  9. #19
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    Quote Originally Posted by ICANHITHIMMAN View Post
    Not saying your wrong, just never heard of it.
    I know. I wasn't calling you out or anything. I was just providing my point of view.

    Quote Originally Posted by markm View Post
    I bet it's negligible... but I could see how a full profiled barrel would absorb more heat and have the potential for a slight reduction in port errosion.
    Agreed. Negligible. But I think it's there.
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  10. #20
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    Quote Originally Posted by ether View Post
    Your question is a really good one though, if I understand it - would gas port erosion start to affect reliability before throat erosion ever would?
    Nope. The port erodes at the bottom... the top of a high round count barrel still has about the same diameter it always had and thus the gas flow isn't really changing.
    "You people have too much time on your hands." - scottryan

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