Anybody drilled and tapped a standard valve for a fill gage?

I will look at doing this to one of my valves when I get home so I can have a fill port and pressure gage on an old style valve. Any one done that to theirs before? Drilling and tapping is easy but if it will remove too much metal and cause the valve to fail then I am all about not doing it. Last thing I want is a 3000 psi grenade going off next to my head.