Hi guys.
Does anyone know if there is enough clearance from the end of an MCMR 13 to run a surefire RC2/mini 2 on a 13.9” barrel?

the closed tine warcomp will work. it has a longer neck copared to the others. i haven't done it but there is enough out there on the web that show it works. without that you will likely have to shave down the sides of the handguard that extend.

i would also like to add, when i was doing my 13.9 build. i had three barrels at one time decided what to do. Criterion Core, BRT HF Optimum, Centurion Arms CHF LW. I ended up chosing on based on gas port size and profile. Core is the best profile, but had a 0.078 gas port size, Centurion LW had the worst profile (still love centurion barrels) but had the best gast port size of 0.074". the BRT had a great profile and good as port size of 0.075". wish centurion had a better profile or midweight 13.9. anyway, i was test fitting them all on my upper and the core was shorter than the rest. i know they call them 13.9 but it was noticable. i didn't torque it all down but a good hand tightbarrel nut and rail installed you couls tell the core was short so i would of had to use more shims. the BRT and Centurion looked identical to me. this was before test fitting MD.

another thing to note some threads are longer and some are shorter. i have seen some threads on the end of the muzzle as short as 0.4205" and some as long as 0.701". general rule is always use .5 inches for threads when determining length of MD to see where you stand but i tend to use 0.6"

Looks like you have to use shims to space it out, or chop the rail. Edit: xFREDx beat me to it.

Shims:


Link to thread: https://www.ar15.com/forums/ar-15/Help-with-BCM-MCMR-13-handguard-fitment-on-13-9--with-a-NOX-muzzle-device/12-773826/

Chop from Reddit:


Reddit link: https://old.reddit.com/r/ar15/comments/ulwrq2/bcm_mcmr_13_chop_for_139_criterion_barrel_to_fit/?rdt=63902

It won’t work.  I mocked one up and the 3&9 sides stack out to far.  I got a 13.1 ripcord and it gives you just a smidge of room to back your collar off on the Surefire.

Ripcord rail

If you are planning to pin & weld, you will need to add ~.2” spacer to a SF3/4P to get to non-NFA length

That spacer might buy you the clearance, but it is going to be tight. Safer option would be a 14.5” barrel, which doesn’t have clearance issues.

I may, but sounds like a moot point.  Only reason I am interested is because I have a current set up with a 16 inch criterion core series barrel, and a 13 inch MCMR. If it wouldn’t work with the current rail, I would love to get it as short and as close as possible to the MCMR but if that’s not possible, I will either go with the 14.5 as you suggested, or simply get a 15 inch MCMR

Much obliged to you and to everyone else who commented to help me with this.

I have a Criterion 13.9 with an MCMR13... Had to use the CT Warcomp to make it work right.

@paulrad

Whew! Talk about close.

Damn that's close! I have some shit that's pretty close, but nothing like that