The following is from an article by Bob Seijasicon " The Type 2 National Match, Part 1", found in the GCAicon Journal:
" During 1957 the accuracy requirements of the NM rifle were toughened by increasing the test firing groups from 5 shots to 10 shots. Rifles subject to the new stricter test were marked with a STAR next to the NM inscription on the barrel between the rings of the gas cylinder. This requirement (the 10 shots) became standard, and the star marking was dropped in 1958. It may still be found on later M1s if the original barrel remained on the weapon when it was upgraded to a later configuration." So as you can see, this star marking had nothing to do with a "star gauge".