I think the X’s were an attempt at quality control. I owned a beautiful little Mowrey squirrel Rifle in .45 caliber. It was one of the earlier models, and it was beautiful, with curly maple stocks, and their eye catching brass box lock. But the reason I got it second hand, and cheap, was that it shot about two feet to the left. Sight adjustment was barely possible by moving the sights to the edge of the barrel. Eventually I made a set of sights that fit the barrel, but had their blade, and notch one the edge of the barrel. I believe whoever made the barrels didn’t mark the run out on the early production.
Hungry Horse