Your go gauge was a round of 303 I’ll presume
You presume wrong. When I first started out I had a professional gunsmith check the head spacing. Later as I got my into it I bought my own gauges, etc.
Point is, do not risk damaging a good firearm until you know what you are doing. I do not know how many I have seen where an amateur was just going to "polish the feed ramp" on a 1911 and ended buying a new barrel.