I sure hope you mean .50 caliber.
Because if not you either mean .5 mm, which is teeny tiny, or 50mm which is overkill.
50 caliber is of course, .50 inches which is about 12.5mm
I love you Americans. The right to keep and bear light artillery.
Of course, that IS envy speaking
That sort of thing would get a guy put in jail up here in Canada. It must be a hell of a lot of fun!