RTB has several barrels that according to internet lore are OEM’d by Ballistic Advantage.

I opened and gauged their 13.9” midlength pencil barrel today. It has a .625” gas block journal.

I started with a 0.079 pin gauge; it entered and stood freely but did not drop through. (Pic below)

The 0.078 pin dropped through. I did not grab a picture.

Note that SOLGW sizes their 13.7” midlength to .0785.