Double X does mean no run out, which is why it isn't stamped Douglas on the breech. They aways stamped the breech so you knew which flat to put on the bottom. The numbers on the muzzle are the caliber, and rate of twist.
I have a 15/16" .45 with a 1 in 66 twist, it is marked Douglas on the breech. The run out is so slight, that you can hardly see it with your naked eye. They recommended you cut an inch, or two off the muzzle to eliminate any irregularities caused by unsupported tool run out, when the rifling was done.
Hungry Horse