20" upper / Carbine lower question.

[missingAZ]

I have a question for a "AR guy"...

I would like to put a 20" barreled upper on my lower that has a collaspable stock with an "H" buffer. All rifle length ARs I have seen have the rifle buffer and reciever extension. I don't like rifle length stocks and want to know if a 20" barrel on a collaspable stocked lower will work? Any of you have a setup like this?

Just for clarity, I know the rifle/carbine lowers are the same the issue I am concerned about is the rifle vs. carbine buffer/reciever extension.

Thanks for the help,

-James.

 

[SKYWLKR]

I asked the same Q a while back and got an affirmative response.

 

[103M 95G]

I know a bunch of guys that have built them this way, and they seem to run fine.

 

[Richard in LA]

I know a bunch of guys that have built them this way, and they seem to run fine.

yep. My 20" ers run fine on a lower with a UBR stock and standard weight carbine buffer, and also my 11" runs fine with a rifle stock & buffer too.

 

[missingAZ]

Thats what I wanted to hear.

What is the relationship between barrel/gas system length and buffer weight?

-James.

 

[Richard in LA]

Thats what I wanted to hear.

What is the relationship between barrel/gas system length and buffer weight?

-James.

In a nutshell, the shorter the barrel, (in front of and behind the gas port) the larger the gas port is, thus increasing the pressure that is allowed to push the bolt carrier back. If you have a short (say 7.5" or 9.25") barreled upper, and a standard weight buffer, the bolt moves back (and then forward) too fast, and malfunctions occur. The heavier buffer slows down the bolt to eliminate the malfuncitons.

If you experience any problems, I have a brand new, standard weight buffer if ya wanna swap for that H buffer.

 

[missingAZ]

Thanks for the info Richard.

-James.

 

[LACamper]

My 20" runs fine w/ a collapsable stock. No complaints! I put a Clark carbon fiber freefloat tube on to keep the weight down.