you only need a go and nogo gage. the field isnt neccessary.
there is no shortcut around this. only thousandths of an inch turn a rifle from a rifle and into a bomb.
"Gun control: The theory that a woman found dead in an alley, raped and strangled with her panty hose, is somehow morally superior to a woman explaining to police how her attacker got that fatal bullet wound." L. Neil Smith
The problem with being stupid is you cannot simply decide to stop doing dumb things...