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Thread: AR-15 BUFFER question........???

  1. #1

    Default AR-15 BUFFER question........???

    Looking for a short education on relationship of buffer weight & spring to gas system. Example could something get damaged putting a mid length upper on a "Pistol" lower.

  2. #2
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    The location of the gas port on the barrel, typically 7" (carbine), 9" mid-length or 12" (rifle) determine how much energy slams the bolt carrier back. Carbine length has much higher pressure at the port thus needs a stronger spring and different buffer. The pistol lower I don't know what spring is used, I'm thinking the gas port location applies, but with the bullet leaving the barrel sooner, pressure drops quickly so likely lighter and shorter spring than would be used for a the same port length in a rifle. I haven't learned actual spring weights vs configurations. I believe the buffer matched to the tube length. Carbine length and pistol length are the same in what I've seen. All NFA rules apply here. Turning a pistol into a rifle may give you an over-all-length problem.
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  3. #3

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    Quote Originally Posted by Murphy View Post
    All NFA rules apply here. Turning a pistol into a rifle may give you an over-all-length problem.
    Thanks for the reply, I just recieved my 12.5" (6.8SPC) Noveske Upper, and want to mount it on a RRA "Pistol Only" lower.

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    There is one differance between a rifle and pistol lower...spelling. The uppers however can be put together in a lot of different ways. Noveske should send the proper set up for the upper if it is different from the carbine but I'm just guessing at that. It's most likely a carbine length so you need a carbine length buffer tube and not a pistol length. Or, some other way to control the recoil.

    With the 12.5" barrelled upper you could have a carbine or a pistol gas tube length, but it is probably carbine so try using a carbine buffer and a carbine spring and see how it works. If you are having problems you may need to go to a heavier spring, buffer or maybe a rifle length spring cut back some or an adjustable gas block or whatever it takes to fix the problem.

    Some barrels can have a smaller gas tube hole to reduce the amount of pressure that acts upon the bolt, therefore the spring wt and buffer can be lighter to match. It's not always simple.
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  5. #5

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    Thanks Lowrider, Is there something that could get damaged with the wrong buffer/spring......? Or is it just a failure to cycle problem....?

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    Probably not. You'll know pretty quick if the bolt is bottoming out in the buffer tube or if it is getting slammed so fast that it won't pick up from the mag or not going back from the firing position enough to pick up a round. Pistol uppers can be frustrating sometimes and I usually use a carbine buffer tube just because it works better with less drama. With a 12.5" you can even shoulder the buffer tube if you like...just don't put a stock on the tube with that $200 dollar stamp for the SBR.
    Somewhere along the way I have lost the ability to act politically correct. If you should find it, please feel free to keep it.

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