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Thread: Proper Buffer for 20" Rifle Gas Upper on Carbine Lower?

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    Proper Buffer for 20" Rifle Gas Upper on Carbine Lower?

    I want to put a 20" A4 upper on a lower with a carbine receiver extension with a collapsible stock. What is the best buffer for reliability? I've been reading a lot about it but I keep seeing answers all over the board. One respected manufacturer has recommended the standard Carbine buffer when using their 20" rifle gas upper on a carbine RE lower.

    I've read that the Canadians with their C7A2 use a "HH" buffer, which I can only take to mean "H2". However, there are many threads of people having problems with H2 buffers and rifle length gas systems.

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    “God doesn’t need your good works, but your neighbor does.” - Luther

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    Edit - the post below addresses carbine length buffers very well.

    If you are building the lower, I would suggest an A5 system, which was designed for your stated purpose. I shoot a 18" rifle with an A5 RE, milspec rifle spring, and A5H2 buffer. It works very well with a wide range of ammunition. I changed the barrel from a 20", which ran perfectly with the set up for 2 years.

    Andy
    Last edited by AndyLate; 09-24-19 at 06:33.

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    My first question is why? Is it to reduce OAL? Do you not have a rifle length lower?

    Second question is do you have a carbine lower you can try out? Friend, relative, LGS, etc.? Depending on how it feels and orientation of ejection, I could suggest which way to go for a purchase.

    In general, the Carbine H2 buffer is the closest approximation to the standard rifle buffer system, but the spring rate is higher and thus may not work with all ammo pressures (typically on the lower side). You're going to have to test the system to see what works for you. If you have no means to experiment with someone else's setup, you could buy a standard carbine buffer and a H3 (or buy the individual tungsten weights to swap with the steel weights). This way you can tune the weight for the ammo you shoot, the spring you run, and the GP size of the barrel. These variables could be why you are seeing mixed answers.
    Last edited by tehpwnag3; 09-16-19 at 13:28. Reason: Spelling

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    Well guys I can say I have an 18" (obviously rifle length gas) that I've been running with a collapsible stock and a standard carbine buffer.

    Just tripped the 1,000 round mark, it has never malfunctioned with any of the plethora of ammo I've put through it.

    Runs and handles fine. I can't see a reason to go heavier.

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    It's not a one-size-fits-all situation. You could probably go heavier, perhaps much heavier, if you ran a can and/or 5.56 exclusively. Then again, maybe you can't, and that's the point. If you don't have extra buffers laying around, I'd say you're pretty lucky or got good advice.


    Quote Originally Posted by ViniVidivici View Post
    Well guys I can say I have an 18" (obviously rifle length gas) that I've been running with a collapsible stock and a standard carbine buffer.

    Just tripped the 1,000 round mark, it has never malfunctioned with any of the plethora of ammo I've put through it.

    Runs and handles fine. I can't see a reason to go heavier.

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    Edited - I ate a snickers and will try again...

    It seems to me that folks tend to be negative regarding adjustable stocks on rifle length (18 -20") ARs and I just don't understand it. In my opinion, based on 20+ years shooting M16s, M4s and my own ARs, an adjustable stock makes the AR rifle more suitable for a wider variety of shooters and shooting conditions.

    Andy
    Last edited by AndyLate; 09-24-19 at 21:45.

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    To the contrary, I appreciated your post. I asked why because IME the 20" barrel paired with a standard RE and buffer is very smooth in operation as well as being one of, if not the most, reliable setups to be had. If OP didn't know that, it should be noted. The mix in question can be, sometimes, painfully finicky and I was hoping to reduce grief from out of shear curiosity of the combo. However, I'll gladly help out even if someone wanted to put a 7" upper on a A2 rifle lower. Yep, seen it done and it ran better than the carbine lower it came from!

    Quote Originally Posted by AndyLate View Post
    Edited - did not add anything useful.

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    I will build a fixed stock rifle in the future because I like the way they shoot and look. I just won't share it like I do my current ARs.

    Andy

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    The best buffer is an A5, which has equal or better reliability than the rifle buffer, but requires swapping the carbine RE.

    In general, the 18-20" uppers are gassed to run a rifle buffer, so that means starting with an H2 or A5H2 weight.

    The 20" rifles are pretty forgiving and should run with most reasonable choices.

    Quote Originally Posted by SouthwestAviator View Post
    I want to put a 20" A4 upper on a lower with a carbine receiver extension with a collapsible stock. What is the best buffer for reliability? I've been reading a lot about it but I keep seeing answers all over the board.

    One respected manufacturer has recommended the standard Carbine buffer when using their 20" rifle gas upper on a carbine RE lower.
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