Just got my stamp approved for 11.5" AR build. I wanted to do this on a BCM lower, but when I decided to do this it was a week before the 41P trust rules changed. I registered a Rock River Arms carbine lower that I had instead. The RRA lower has a commercial tube with a standard buffer and spring for a 16" carbine. I am looking to mate it with a BCM 11.5 upper, or a Colt LE6933CK 11.5 inch Commando Upper Receiver.

My question is do I need to get a Mil-Spec buffer tube with an H2 buffer, or can I put an H2 buffer in the commercial tube? Do I need to run a different spring, or will the carbine spring work with the 11.5" barrel?

Any help would be appreciated. Thanks.

you are good to go with any buffers, outside diameter is a bit larger on the comm tubes, stocks are the only thing to worry about

I'd drop an H2 in your existing lower setup and call it good.

Thank you for your help with this

As others have said, no worries at all by just dropping in an H2 in to the commercial tube.

If one felt inclined to change buffers just because, a great idea would be to swap to the A5 system, but not really needed.

I've got an H3 in my 11.5 BCM-upper SBR, runs great.

IMO, better route is to leave the lower as is and use an adjustable gas block to reduce cyclic rate with or without a suppressor.

Smoother recoil, minimal felt recoil, minimal gas in the face.

JPK

I use a H2 with my BCM 11.5" inch. So far it works 100% regular and suppressed.

Thank you everyone for your helpful information. I am going to keep th commercial tube/spring, and install an H2 buffer.