According to Poyer's 'The Model 1903 Springfield Rifle'... Beginning in 1905, an interior gauging system was installed at the Springfield Armory to provide precise measurements of the bore.  Referred to as a "star gauge," it was a hollow tube with arms at one end that could be expanded by pushing a rod into it to force the arms against the land or grooves.  The amount of expansion was read at one-inch intervals directly from a dial indicator.  A statistical sampling was made of service-rifle barrels during production runs to ensure that they did not exceed maximum and minimum standards.  Beginning in 1921, barrels so gauged had a tiny eight pointed star stamped on the crown at the six o'clock position.  Additionally, beginning in 1921, all barrels for competition were star-gauged and so marked on the crown.

BTW: Star-gauged rifles are highly desirable and sell at premium.

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