AR-15 buffer weight - what weight to use full length upper + "carbine" lower.?

As far as I can tell in order for a full length (full length gas system) upper to function correctly with a carbine length buffer tube it needs to be equipped with a heavy or H2 buffer, does anyone have first hand experience with this combination and if so what equipment did you use?

Added - Don't tell me it can't be done or its not safe, Colt Canada makes all their full length rifles on contract for the Canadian Army with "carbine lowers" and full length uppers.

6 Answers

  • 10 years ago
    Favorite Answer

    Jamie Lynn has the data. I will add my own build experiences and opinion:

    1) Remember that the buffer is only half of the buffer system. The rifle has a heavier buffer but a weaker spring. The carbine has a lighter buffer but a stronger spring. You might need to go to a carbine spring if you use a carbine buffer in order to maintain reliability.

    2) The heavier/stiffer the buffer system, the more impetus required to cycle it. This is a delicate balance. If it's too heavy, you could short-shuck. If it's too light, it beats itself to death. Jamie Lynn's recommendation to go middle of the road is a safe one in most cases with carbine length. Remember to mind the spring, as well.

    3) The other reason to change buffer weights and spring tensions in the buffer tube is to adjust cyclic rate on full auto. On an AR-15, this point is moot as it does not have full auto capability (Except for the early AR's..but let's not get into a nomenclature discussion...for the sake of simplicity in this particular context, I refer to civvy semi-auto AR's as AR-15's and military select-fire AR's as M16's) so you need not worry about bolt bounce associated with cyclic function.

    4) I have had firsthand experience with nearly every legal configuration of AR-15. My rule of thumb has always been: Rifle buffer tube, rifle buffer and spring; Carbine buffer tube, carbine buffer and spring.

    I would suggest matching buffer to spring (rifle/rifle, carbine/carbine) and then going from there.

    Want to be safe? Take Jamie Lynn's advice. I'll second her data as accurate.

    Edited to add: I will add URLs of pictures of a full-size rifle buffer vs. a carbine buffer so the difference is easier to discern.

    Carbine buffer (Courtesy of Brownell's):

    Rifle buffer (Courtesy of Black Weapons Armory)

    Note the extra length of the rifle buffer. If used in a carbine-length adjustable buttstock tube, the extra length will not allow the action to cycle.

    To be noted: The AWB FIXED "Collapsible" stock actually uses a full-length buffer tube (as it is not actually collapsible) and thus may use the rifle buffer.

    You can use a carbine buffer in a collapsible or non collapsible stock with the appropriate carbine spring.

    Source(s): (Carbine buffer picture) (Rifle buffer picture) I, too, build AR-15's as a hobby and have been doing so since 1997.
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  • teeple
    Lv 4
    3 years ago

    Ar 15 Rifle Buffer Tube

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  • Anonymous
    10 years ago

    For the carbine lower, there is no full size buffer tube. It is "carbine" size and comes in fixed, 5 position and six position. If you have a standard m16 style butt stock you would have a standard,non carbine buffer tube though. Any ar15 upper will work on any lower reciever, as long as the upper and lower are for the same caliber such as 5.56..

    As far as weight goes, there are typically four weights:

    The regular carbine buffer has 3 steel weights, - 3oz

    H is 2 steel, 1 tungsten - 3.8oz

    H2 is 1 steel, 2 tungsten - 4.6oz

    H3 is 3 tungsten - 5.4oz

    I find the middle of the road to be the 4.6oz and tends to cycle less harsh with the carbine gas system.

    Source(s): building ar15 rifles for 10 years
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  • 10 years ago

    Did I miss something?

    For 40+ years the US Military has not had a separate part number for the carbine and full lenght rifle buffers.

    And the last 20 years I have always interchanged my buffers between carbines and full lenght with no issues.

    To my knowledge - the only reason to go with a heavy buffer is to slow the cycle rates in full auto lowers, and, to reduce the buffer impact when with higher pressure ammo - like the 77gr Sierra, 80gr Berger, 90gr Sierra and 100gr extreme shocks.

    If it aint, broke - why fix it?

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  • 5 years ago

    For most 16" M4 type the H buffer is standard issue.

    For MK 18 type with 10.3" barrels the H2 buffer is most common.

    For MK 12 type with 18" barrels the H buffer is the most common with 102" gas port size.

    For M16A2 with 20" the H2 or H3 will work or the new H6 buffer from Damaged Ind.

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  • Elaine
    Lv 4
    4 years ago

    Next time your at a gun show, pick up some Official U.S. Military armors manuals. These are good to have BEFORE you even begin to build the rifle. ( I believe there are three manuals to the complete set ) All the torque specs. and such are in there. It describes what specialized tools are needed. I highly suggest even if building a shorty to purchase the 20" barrel rather then the 16 ". Then you have essentially the full-sized gun in a compact package. This does somewhat better over a longer range, just as the full-sized rifle does compared to the shorty. Edit : AND thank you , for wanting to learn more. Very admirable Ma'am.

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