Does anyone know if the post-ban Colt MT 6400C (M 4 carbine) has a threaded barrel?  I want to replace the pinned in compensator with a standard bird cage flash suppressor but don't know if I will have to have the barrel threaded to do so.

The brake on the MT6400C is a slide fit on its plain (non-threaded) muzzle that is secured by two roll pins on the earlier models and two solid pins on later manufacturer. The muzzle o.d. measures about .701" under the brake and for a short ways farther back.

The pins are very easy to punch out, and the brake will easily drive right off. If you encounter the least bit of resistance driving the brake off just fire a couple of rounds theough it (with the pins removed, of course). Many of the roll pin models blew the brake off with the pins still installed .

When you remove the brake you'll need to turn the barrel o.d. down to .498"-.500" for a distance of about .610"-.625" (about 5/8") so you can thread it 1/2-28tpi which will allow it to accept any AR-type FH.

I found it an easy job, having first done it to my personal MT6400C and then to several more belonging to friends. If you don't have access to a lathe, or the skill to use one, you can still remove the brake and send the barrel to a shop that can thread it for you.

HTH

Quoted: Does anyone know if the post-ban Colt MT 6400C (M 4 carbine) has a threaded barrel?  I want to replace the pinned in compensator with a standard bird cage flash suppressor but don't know if I will have to have the barrel threaded to do so.

As the earlier post stated, its not threaded. You should be able to get it threaded.