The NM shown is pantagraphed. It was something like a dentist drill on a pantagraph machine that followed a pattern and cut the same pattern on the piece to be marked.
Not sure what the star was for. By the time the NM M1 rifles were made the barrel was air gauged. The old star gage relied on the person doing the gauging feeling the difference in the barrel, where the air gauge has a metered amount of air pressure applied to a plug that fits the barrel. Any increase or decrease in air pressure as the plug passes through the bore indicates tight or loose places in the bore.