I am assembling a new 20" barrel upper and would like to put a 6 position adjustable stock on the lower. My question is what weight buffer should I try - carbine, H, H2 or H3 with the rifle length gas system? Anything specific with the spring?
Thanks
Jimbeaux
A5 RE 
no comprende
H2 is most appropriate.
Edit:
And the “A5 RE” mentioned in the post above mine refers to the VLTOR A5 system.
I would use the A5 system.
Whether you use a standard carbine RE or the A5, the buffer weight you want to use is what’s closest to the rifle buffer weight, which is (if I recall) 5.3 oz
A5 gets my vote. (Another very happy A5 user here.)
If you are not going to use the A5 buffer system, use an H3 buffer and USGI or blue Sprinco spring.
What Ryno12 said.
Thanks for the info. I will consider the Vltor system.
Meanwhile, I went to the range to test fire my new upper. The upper is a PSA Premium 20" with the FN chrome lined barrel. I mated it to a PSA lower, with normal 6 position adjustable stock, carbine spring and carbine buffer from one of my carbines. I had an H and H2 buffer with me if the carbine buffer showed problems. However, didn’t need them. With the standard carbine lower, the rifle ran like a champ with 5 different types of ammo, 2 handloads and 3 factory. No ejection issues, no feed issues, no issues locking back. This being my first 20" rifle upper, I was surprised by the smoother operation and lesser or more spread out recoil. Really felt nice. Rifle really liked PPU 75 gr BTHP match, shooting MOA at 100 yds.
May try the H2 buffer just to see how it shoots. Might smooth out the recoil a bit further.
Jimbeaux
The longer barrels and gas systems seem to be more forgiving of light buffers, but can still benefit from them.
Try the H2 next time out.
I have run 20" rifle with a .093 port on a Carbine, H, and H2 buffers just fine, though I think the H2 ran the best.
Currently I run 20" stuff on A5 H2.
In all reality theres no reason to run anything other than A5, no matter what gas length/barrel length. Just buy it, it will work with anything.
This. I ran a 20 inch with a carbine RE and a carbine buffer for awhile and it was pretty good. But I didn’t know as much back then and didn’t realize the difference in mass between the carbine & rifle buffers. Once it dawned on me, I tried an H2 and saw an improvement in felt recoil.
Now, I’m running it with an A5 RE & buffer and she’s that much smoother and jumps around that much less during recoil. I’m sold. I plan to get the BCM 8 position A5 style RE for the carbine
I always use the heaviest buffer I can get away with. I have a MILSPEC 20" FN barrel, with an LMT enhanced carrier and an A5H3 inside with green Sprinco and it runs just fine. There are other things to think about aside from just “recoil”.
That’s a good point, IG. If the BCG doesn’t have enough mass and enough momentum, feeding won’t be as reliable or as smooth
The Canadians run theirs with an H2, the Americans use an H6.
I’ve used an H2 and a standard A5 with no trouble out of either with a BCM 20" A4 upper.
In terms of function with appropriate porting on a 20" 5.56 AR type rifle, the highest reciprocating mass that functions within the required parameters would suit most users better, that is unless certain things like some sand tests could take priority. A reduced mass could increase the span of function in some situations if other other variables are added in, like reduced gas port pressure ammunition, etc.
The Army H6 buffer weighs 5.15 oz. The H3 carbine buffer weighs about 5.4 oz. In the real world, assuming you have a properly built rifle and use good ammo, .25 oz makes virtually no difference.