Black Hole Weaponry's Dragon Head muzzle break was backordered, I cut the end off the thread protector that came on the barrel, and left it on to prevent screwing up the threads.
The 6 TCU is a good one, but it is not designed for the AR, the OAL is not setup to fit mag length. You have to seat the bullets so deep, that you could have close to a 1/2'' jump to the lands with a VLD. If you want a 6mm based on a 223 case I would go with the 6x45, I have one, it is very simple to load for, and it is a deer and hog hammer.
My nine year-old daughter has claimed the 6x45, so I decided to build something based on the 223 case that had more punch, and I am huge 6.5 caliber fan. So the 6.5TCU is where I started looking, realized quickly that to make it work in a AR and fit 120gn bullets it had to be tweaked. Neck had to be shortened, throat had to be shortened so it would not have such a jump to the rifling. A buddy and I engineered it, bought the reamer, sent it to BHW.
I got my 18'' about a month ago, and built my buddies 22'' for testing last week. Accuracy has been great, although I am doing load testing, and only shooting two shot groups. Top speeds with a 120gn hot-cor so far have been 2441fps with the 18'', and 2510fps with the 22''.
Here is a 100 yard target from my last session.
The 18'' and the 22''