Current 6mm Grendel barrel makers: BHW, McGowen and who else?

[grayfox]

Last week I ordered the BHW/Columbia 6X45 1X9 18 B/R TC MACH for $91.25 shipped.
Today, I bought five uppers, a BCG and some gas blocks and gas tubes for other builds.
Don't need no muzzle break for the target crown.
I plan to put a schedule 40 handguard on this build.

I bought some RCBS 6x45 dies from Midway this week as well as 3 different types of 6mm bullets.

The extra upper I bought is reserved for the group buy of the 6mm AR turbo improved.

1/9 or 1/10 or which other... one of my questions is what twist rate is preferred. I was -- idly -- looking at a 20" barrel but still not quite ready to pull the trigger. Or the 6mm mongoose, which I think is a 6mm Grendel wildcat.