[Fishinkeylargo]

Anyone running a 20" upper on a carbine length lower? What size buffer are you using? I have read mixed responses from many different forums, but can't seem to find a response from anyone actually running that combo.

 

[dayvedayve]

I have a friend that I help build 20" barreled AR. We put his lower together and used a regular carbine buffer that came in the lower build kit with the Magpul MOE stock. It ran flawlessly using both 5.56 and .223. We ran both Federal and Tula 223 and didn't have any problems. You should be good to go.

 

[parad0x177]

I've got a custom 18" barrel, rifle-length gas system, carbine-style buffer/stock, and FA carrier. It runs fine with a standard weight carbine buffer, but shows signs of being a little over-gassed. (bounces brass off the deflector) Your mileage may vary, but I've had better luck with an H2 buffer in it.

Assuming your barrel uses a standard port size (like all of mine), the longer barrel could (theoretically) lead to even more over-gassing from the longer dwell time. So, that in mind, I'd suggest starting with an H2 buffer. That will get you very close in weight (within an ounce as I recall) to a standard rifle buffer without going over. It's possible you could still be a little over-gassed, but I suspect that will leave your reciprocating mass low enough (even with a FA carrier) to cycle reliably with any standard .223 or 5.56 load. Then, if you find it still over-gassed, you can always go to an H3 later.

Good luck!

 

[Fishinkeylargo]

Thanks for the input. I have plenty of time to do more research, the buffer is the only thing I need to complete my lower so I may just pick an "H" and start there.

 

[Lmstncwby]

Get an H2 and an H3 buffer just in case.