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Thread: Long stroke VS. short stroke gas piston system?

  1. #21
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    Quote Originally Posted by Coleslaw View Post
    I beg to differ. By design the AK can "ead dirt" in better fashion than the M16.





    So you are saying that LWRC 10.5" uses a short stroke and an LWRC 14.5" uses a long stroke. You are mistaken, LWRC uses only short stroke. The 14.5" uses their mid-length system which amounts to a longer intermediate rod, but it is still a short stroke.
    No not saying they have a long stoke, i understand they use a short stoke design, just saying that the mid length system has a softer kick than the 10.5 short stroke system, not a big difference or really even note worthy but its there.

  2. #22
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    There may be no formal definition of long stroke or short stroke, but here is mine.

    I think that a long stroke piston is powered by bore pressure over all or most of the complete length of the operating cycle. Two that currently come to my mind are that of the M1 rifle and the FAL. The piston end of the op rod is contained in the gas cylinder for the entire cycle. THERE IS NO VENTING OR SHUT OFF AFTER THE PISTON BEGINS THE STROKE. The FAL has an adjustable vent at the beginning to regulate the pressure. The M1 has no vent.

    As far as I know, most other current and successful designs are short stroke in one way or another. Either they have a separate piston that has a much shorter cycle than the carrier-locking lug assembly or they are vented or both.

    The AK, H&K, and M16-M4 are vented shortly after the piston begins the cycle. In the case of the M16, it is the cylinder that moves and the piston is the bolt head, which does not move under gas pressure.
    Dave

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  3. #23
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    I always thought it was pretty simple in that long-stroke were generally indicated by the rod attached to the carrier and short-stroke were generally rods that strike, or push, the carrier. AK being long-stroke, FAL being short-stroke.

    Someone earlier in the thread said that long-stroke was the piston moving a distance equal-to or greater-than the length of the case and short-stroke was the piston moving a distance less than the length of the case, which would go hand-in-hand with my definition as well.

  4. #24
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    Quote Originally Posted by Coleslaw View Post
    I beg to differ. By design the AK can "ead dirt" in better fashion than the M16.
    This is due to the very large open area and clearances of the fit between the bolt carrier and receiver. The carrier just rides on two sheet metal rails in the sheet metal or milled receiver instead of a carrier in a cylindrical mostly closed up upper receiver. Apples don't equal oranges.

    I appreciate the design of the AK it's a great gun (I own a few of them), it isn't the same as an AR. It's not quite as easy to change calibers, use good optics and lasers etc with an AK. With an AR I can go from .22LR, 5.56mm NATO, 6.8SPC, 6.5Grendel to .50 Beowulf in about 1 min. Not so with the AK.
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  5. #25
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    Quote Originally Posted by rob_s View Post
    I always thought it was pretty simple in that long-stroke were generally indicated by the rod attached to the carrier and short-stroke were generally rods that strike, or push, the carrier. AK being long-stroke, FAL being short-stroke.
    .
    That's my working definition as well.

    However, I'll throw it out there that it doesn't really matter.

    The most meaningful difference between various systems is: how long the gas system is under pressure, or short impulse vs long impulse.

    The most obvious manifestation of this is the barrel length from the gas port to the muzzle. ( sound familiar ?)

    Once the bullet un-corks from the muzzle, the game is over, and whatever work needed to get done better have already been done.

    A piston that has one inch of bbl after the gas block, has a lot of work to do in a very short period of time, a short impulse design.

    The AR, seems to be one of the longest & softest impulse designs around.

    Another example, the "long stroke" AK, will operate happily with the " gas tube" ( really just a piston guide ) removed.

    The only powered travel is roughly .75", just when the piston is inside the gas block, before the radial gas ports are exposed.

    The thing that really controls the " dwell time" is the barrel length ,velocity of the round and any gas storage effects the system may have.

    This is what most suppressors and the KX3 do, increase dwell time and increase the overall impulse delivered to the piston.

    The gas port diameter controls the "rise time" ( how quickly it ramps up ) and fall time of the pressure in the gas system.
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  6. #26
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    Quote Originally Posted by Clint View Post
    That's my working definition as well.

    However, I'll throw it out there that it doesn't really matter.

    The most meaningful difference between various systems is: how long the gas system is under pressure, or short impulse vs long impulse.

    The most obvious manifestation of this is the barrel length from the gas port to the muzzle. ( sound familiar ?)

    Once the bullet un-corks from the muzzle, the game is over, and whatever work needed to get done better have already been done.

    A piston that has one inch of bbl after the gas block, has a lot of work to do in a very short period of time, a short impulse design.

    The AR, seems to be one of the longest & softest impulse designs around.

    Another example, the "long stroke" AK, will operate happily with the " gas tube" ( really just a piston guide ) removed.

    The only powered travel is roughly .75", just when the piston is inside the gas block, before the radial gas ports are exposed.

    The thing that really controls the " dwell time" is the barrel length ,velocity of the round and any gas storage effects the system may have.

    This is what most suppressors and the KX3 do, increase dwell time and increase the overall impulse delivered to the piston.

    The gas port diameter controls the "rise time" ( how quickly it ramps up ) and fall time of the pressure in the gas system.
    I have seen this train of thought before what long stroke rifle has a long impulse? From what I can tell the ZB26,Bren,BAR,PKM & AK all vent the gas early IE short impulse. I am sure some where in the firearms world there has been a long impulse design but the above represents to the world what long stroke operating system are.

  7. #27
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    Quote Originally Posted by Coleslaw View Post
    I beg to differ. By design the AK can "ead dirt" in better fashion than the M16.
    Not in my experience. There are issues with the trigger group if dirt gets in there (the AK).
    Last edited by 87GN; 12-05-10 at 23:55.

  8. #28
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    My experience is the exact opposite. The AK can take a substantial amount of dirt and abuse, more so that most other systems. It can also remain functional with little if any maintainance.

    I recall a 'test' done on a whim about 25-30 years ago with an AK. A fellow took about (IIRC) approximately 5-6 small-med marbles, dropped them into the receiver, insterted a mag, and proceeded to run the rifle through it paces w/o any problems. Removing the top cover after shooting several mags revealed that much of what was left of the marbles was small pieces. I can't say the same results would be realized every time if this was done, but just the fact the receiver would accomodate the marbles is something.

  9. #29
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    I took fine sand and poured it into the side of the receiver. The AK stopped working. I had to open the receiver of an AR and pour sand inside to cause problems. Even then, the trigger just didn't reset and could be pushed forward with a finger to reset.

  10. #30
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    Colt made a Long Stoke piston (Colt's initial M16A2 concept gun of the late 60's or early 70's). We have a few here, the piston is part of the bolt carrier (well it links into it).
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