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Thread: Carbine vs. Middy: Real world use

  1. #91
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    Quote Originally Posted by Iraqgunz View Post
    Isn't port pressure also affected by the length of the barrel and the location of the port? Or am I thinking of chamber pressure?
    Mk18 means that at ANY GIVEN port location... you can only change pressure with chamber or ammo differentiations...

    Of course relocating the gas port would change it.

    You can't even change the port pressure if you make a middy out of Carbine and blow your handgaurds off the gun!!
    Last edited by markm; 03-31-11 at 13:14.
    "You people have too much time on your hands." - scottryan

  2. #92
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    Quote Originally Posted by markm View Post
    Mk18 means that at ANY GIVEN port location... you can only change pressure with chamber or ammo differentiations...

    Of course relocating the gas port would change it.

    You can't even change the port pressure if you make a middy out of Carbine and blow your handgaurds off the gun!!
    Nailed it!

    Quote Originally Posted by Iraqgunz View Post
    Isn't port pressure also affected by the length of the barrel and the location of the port? Or am I thinking of chamber pressure?
    Volume/pressure isn't changed by the length of the barrel, dwell time is. Dwell controls the amount of time the available gas pressure has to work.

    Here is something to think about...

    At the fraction of a second that the gas system has reached peak pressure, the gas and particulate matter in it has the consistency of balsa wood.
    Last edited by MarkG; 03-31-11 at 13:54. Reason: Append

  3. #93
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    Quote Originally Posted by MK18Pilot View Post
    Nailed it!



    Volume/pressure isn't changed by the length of the barrel, dwell time is. Dwell controls the amount of time the available gas pressure has to work.

    Here is something to think about...

    At the fraction of a second that the gas system has reached peak pressure, the gas and particulate matter in it has the consistency of balsa wood.
    Balsa wood? That is pretty fascinating.

  4. #94
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    Quote Originally Posted by MK18Pilot View Post
    Nailed it!
    At the fraction of a second that the gas system has reached peak pressure, the gas and particulate matter in it has the consistency of balsa wood.
    I'm sorry, but I am incapable of believing that statement.

  5. #95
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    Ok, gotcha.

    Quote Originally Posted by MK18Pilot View Post
    Nailed it!



    Volume/pressure isn't changed by the length of the barrel, dwell time is. Dwell controls the amount of time the available gas pressure has to work.

    Here is something to think about...

    At the fraction of a second that the gas system has reached peak pressure, the gas and particulate matter in it has the consistency of balsa wood.



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  6. #96
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    Quote Originally Posted by An Undocumented Worker View Post
    I'm sorry, but I am incapable of believing that statement.
    Don't be sorry... Just move along.

    Mike LaPlante of S&W / Colt fame is the source of the information. I don't quite understand it myself but I will take anything he had to say to the bank.
    Last edited by MarkG; 03-31-11 at 18:39. Reason: Source

  7. #97
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    Quote Originally Posted by MK18Pilot View Post
    Don't be sorry... Just move along.
    I guess I should have said; I'd like to see your logic behind that statement, because as far as I know gases/plasmas never reach the state of a nonflowing solid.

    Edit-Quoted post was restated while typing this reply

    I would certainly like to see the research behind his claim, cause that kinda stuff is quite intriguing though I still have trouble believing it.
    Last edited by An Undocumented Worker; 03-31-11 at 18:40.

  8. #98
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    Quote Originally Posted by An Undocumented Worker View Post
    I guess I should have said; I'd like to see your logic behind that statement, because as far as I know gases/plasmas never reach the state of a nonflowing solid.

    Edit-Quoted post was restated while typing this reply

    I would certainly like to see the research behind his claim, cause that kinda stuff is quite intriguing though I still have trouble believing it.
    I think maybe they mean 'consistency' as density? It takes 3 millionish psi for hydrogen to reach a flowing metallic state...

  9. #99
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    Everything I've read prior to this states that the 20" barrel is ideal, since it was designed for the pressure curve of the 5.56 round specifically. Anything shorter provides more gas to the BCG, possibly resulting in bolt bounce. (admittingly more of a problem in a FA weapon)

    Dwell time is important because from the way I understand it, it allows the BCG time to bleed off pressure before unlocking - the amount of barrel in front of the gas port is key. This is why they had trouble with the Xm177E1's and many were run with fixed A1 stocks (heavier buffers).

    The bolt bounce problem was addressed by Colt by increasing the length of the barrel to 11.5" to increase the dwell time, which makes sense to me. LMT has done pretty much the same thing by bleeding off excess gas with their 'enhanced BCG' as well as changing some geometry in the bolt/BC relationship.

    Heavier buffers (H2) were recently standardized in the M4A1 from what I understand, which is essentially the same thing VN era armorers were doing to make the E1 run. From everything I've read, ALL carbines are inherently overgassed. This is why middys and rifles recoil softer, and why there is more stress on M4 components. Anything that can be done to slow down or soften the rate at which the BCG unlocks is a good thing, but there is a limit, and ammo choice/ size of gas port just adds another variable. You can have too much of a good thing obviously.

    Someone who is WAAY smarter than I (Pat of course) posted this years ago, (right here on this forum IIRC) but it makes a lot of sense to me. It seems to me like finding the correct buffer weight for your particular carbine barrel length/gas port size is KEY to making it reliable, along with a better extractor spring and buffer, plus an O ring (or D ring if you like spending money.)

    I really like the idea of the LMT enhanced BC, but again, it's another variable. I'm starting with a standard M4 barrel/port, M16 FA BC (another weight issue - semi BCs are a little lighter of course) and a fixed stock with rifle buffer, which is somewhere around an H3 or 9mm buffer in weight from what I understand, but should have different characteristics. I might have to just go out this weekend and put some rounds through it to see if it has issues. I may buy an enhanced LMT BC just to try if the fixed stock thing works the way I think it will. It may be 'too much', I won't know until I try it. Anyone ever run this combination before? Kind of a modern model 651.
    Last edited by Morg308; 03-31-11 at 21:36.

  10. #100
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    For clarification, is dwell the length of barrel before or after the gas port? Based on this quote I'm guessing its the latter.

    Quote Originally Posted by MK18Pilot View Post
    Volume/pressure isn't changed by the length of the barrel, dwell time is. Dwell controls the amount of time the available gas pressure has to work.
    I was still goofed up thinking of the gas port as a regulator, which i now know its not. I convinced myself with this analogy: the instant before the bullet passes the gas port, the barrel is basically a fixed pressure vessel, like a compressor tank. If I punch a hole in a pressurized tank, air will escape at whatever pressure the tank is at, the size of the hole only determines how fast the tank bleeds off.
    B.A.S. Mechanical Engineering Technology

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