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Thread: Reciprocating mass and the recoil impulse

  1. #21
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    K=1/2MV^2

    You aren't changing the energy in the system. You are only changing V for the BCG and Buffer combined recoiling mass.
    My brother saw Deliverance and bought a Bow. I saw Deliverance and bought an AR-15.

  2. #22
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    Quote Originally Posted by LittleMagic View Post
    I am new to the the AR platform. So please excuse if my question has been answered.

    I have a 16" upper w midlength gas system. I built the lower. Bought the CTR w milspec buffer tube, H2 buffer, and complete upper.

    A few Q's:

    i.) What do I need to do to lessen the muzzle rise and recoil such to get back on target quicker?
    ii.) How do I id the buffer spring, as I am not sure what type it is?
    iii.) Is the H2 buffer too heavy or too light?

    thx in advance.
    In my very limited experience( I've built two rifles one was middy and one was rifle gas) the H@ is probably overkill for a middy. If it is running fine don't worry too much about it. As for muzzle rise a compensator of some type is going to do way more to help than any spring,carrier or buffer changes. You have to decide if you can tolerate the increased noise. I use a Miculek and a Ops Inc muzzel break but both are loud.

    Mule

  3. #23
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    1.) muzzle brake. The FSC isn't that loud, and it also combats flash. Check out www.ar15performance.com for a new tunable brake.
    2.) it's gotta be a standard carbine spring. You probably won't have a problem with it for some time, but feel free to get a Colt one from Specialized Armament for $10, and save yours as a back-up. DO a little Google and find how long the tolerance is, to measure occassionally.
    3.) too heavy, but it might work fine. Use a range of ammo to test, both underpowered .223 and hi-test 5.56.
    Last edited by carbinero; 10-25-09 at 21:23.
    "Men speak of natural rights, but I challenge any one to show where in nature any rights existed or were recognized until there was established for their declaration and protection a duly promulgated body of corresponding laws." --Calvin Coolidge

  4. #24
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    Definitely not an expert, but I took a physics class once...


    The JP and Vltor systems work in different ways to do the same thing: reduce the recoil felt by the moving parts. The JP system reduces the weight of parts and lowers the gas to just what's needed to move them, where the Vltor system puts more spring behind a heavier buffer in a longer tube. Comparing the standard system to the JP system, you now have lighter components recoiling against you at the same velocity that the heavier components were (with less wasted gas). Comparing the standard system to the Vltor system, the Vltor system's heavier buffer is harder to move (greater inertia) and its longer tube houses a longer spring that stores (absorbs) more mechanical energy and exerts more force than the shorter CAR spring.

    JP's system is related to momentum. A lighter object hitting your shoulder at the same velocity of heavier object will hit softer than the heavier object.

    Vltor's system is related to inertia and spring length. A same weight object hitting a heavier (harder-to-move) object with more spring to resist compression (absorb energy) will hit softer than if it had hit a lighter (easier-to-move) object with less spring to resist compression (absorb energy).


    -B
    RIP, Jeff Dorr: 1964 - July 17, 2009


    "When young men seek to be like you, when lazy men resent you, when powerful men look over their shoulder at you, when cowardly men plot behind your back, when corrupt men wish you were gone and evil men want you dead . . . Only then will you have done your share." - Phil Messina

  5. #25
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    People shouldn't be selecting buffers based on recoil.

    Okay.. maybe for gaming guns... but NOT fighting guns.

  6. #26
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    And yet, a change in receiver extension, spring, and buffer was apparently shown in trials to make otherwise-stock carbines (fighting guns) more reliable. JP might've designed their system for game guns, but did Vltor? Did Mike Pannone and others before Vltor who also started using beefier springs and heavier buffers make these changes for game guns?


    -B
    Last edited by BAC; 01-14-11 at 20:45.
    RIP, Jeff Dorr: 1964 - July 17, 2009


    "When young men seek to be like you, when lazy men resent you, when powerful men look over their shoulder at you, when cowardly men plot behind your back, when corrupt men wish you were gone and evil men want you dead . . . Only then will you have done your share." - Phil Messina

  7. #27
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    In Grant's post, Best Suppressed SBR Ever, he discloses that he worked with the sizing of the gas port to give the rifle just enough gas for the action to cycle. He used an LMT enhanced bolt carrier and an H2 buffer.

    What if you built an upper but optimized the gas port size to work with a lightened bolt and a lighter buffer? You would have a reduction in gas pressure from the smaller port and less reciprocating mass.

    What effect would this have?

  8. #28
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    Quote Originally Posted by EzGoingKev View Post
    What if you built an upper but optimized the gas port size to work with a lightened bolt and a lighter buffer? You would have a reduction in gas pressure from the smaller port and less reciprocating mass.

    What effect would this have?
    An adjustable gas block does the same thing but allows to make adjustments if you change ammo. GP size does not let you adjust easily

    With the JP system or a BCG that has been lightened and used with a lighter buffer. You keep reducing the amount of gas until the bcg will not lock back, then add a little more gas. This gives the lightest recoil impulse, light reciprocating mass and the carrier is not slamming back. smooth and light is alway better that smooth and heavy or light and harsh

    To get the most out of a adjustable gas block, you need the proper size GP to begin with. If you are severely overgassed, then the gas will erode the adjustable gas block. I had a 14.5" carbine barrel that came with a GP of .099, no matter what I did, the gun was very harsh and eventually ate thru the adjustable gas block. The barrel I run now is .063 and even with the gas block turned down, I haven't had any erosion issues.
    Last edited by Supermoto; 01-15-11 at 08:42.

  9. #29
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    Two differing approaches to arrive at the near same end point but with a lot of variation in the utility.

    First one must consider what constitutes the felt recoil and the controlability of the rifle. The contribution from the cartridge recoil is usually minimum (except the big bores) and the "felt portion will consist of the acceleration of the carrier group, the bottoming out of the carrier group at the end of the buffer tube and the final stop of the carrier group against the barrel extension.

    Taking the lightweight, the methodology is the minimise the reciprocating mass as far as possible. To work effectively the system timing (port position) must be well set up. The potential energy storage of the system is low so the port size must be small (usually adjustable as it must be carefully tuned to the load). Upon firing the rearward acceleration of the group does little to counteract the recoil from the projectile but equally the change of momentum when the group stops and when it runs forward again, are small so offer little disturbance in the sight picture. With the short reciprocation length of the AR, a low mass with limited spring compression to store energy reduces the energy available to strip a round from the magazine and close the breach. This linear brake effect is useful in retarding the impact of the carrier and subsequent carrier bounce but the gun has little tolerance for field contamination.

    Looking at the approach of using a heavier carrier group this is more applicable to a working rifle as it detunes the system. The heavier group being thrown backwards at firing will act to move the rifle forwards away from the shooter. As long as the base rifle is reasonably timed and gassed, the energy storage of the mass/spring is greater so the group does not arrive at the bottom of the buffer tube with as much velocity. Energy is not wasted in the impact so the ability to strip the next round is enhanced. Overall the energy in the heavier system is greater but the reciprocating mass is greater so the movement of the rifle will be more than the equivelent highly tuned light carrier set up.

    Bill Alexander

  10. #30
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    So with the LMOS, if you use a Tank brake vs an A2 FH, would you need to adjust the gas port for that? Other than different ammo and suppressor use, what other reasons would you need to adjust, using the LMOS system?
    "Men speak of natural rights, but I challenge any one to show where in nature any rights existed or were recognized until there was established for their declaration and protection a duly promulgated body of corresponding laws." --Calvin Coolidge

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