Since Douglas offers multiple grades, it wouldn't surprise me if Wilson did, too. So the comparing of two barrels out of the same plant may not always be quite as apples to apples as you might suppose.
Or note that the Wilson Garand barrels were boasted by Brownells to have been made from Douglas premium blanks. So I'm guessing Wilson had the contouring machinery and Douglas didn't or else asked too much for that part of the work. The military configurations are a good application of the Douglas blanks because they are stress-relieved. I've had a number of inexpensive Garand and M1A barrels and military versions of them with half thousandth constrictions under the heavier portions of the contours, which comes from contouring without stress relief.
I would note, too, that some brands have multiple sources. Savage, for example, uses something I don't know the source of in some grades, Criterion barrels in their match grades, and they were running two cut rifling machines in house when I had a tour of the plant, but I don't know which particular guns those go into. So it's a mixed bag.
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