Probably fairly quickly, but what type of gun are you planning on using? I mean I wouldn't try this with a .22 or something. Shotgun and buckshot is best. You won't miss with a shotgun barrel in your mouth. Well, unless you simultaneously pull the gun out of your mouth at the exact same time that you're squeezing the trigger. Don't do that. Be sure ahead of time that CTB is truly what you want. If there are any doubts, don't go through with it until if/when those doubts are gone.