The gun shots marked both the beginning & end of a show, (judging wise) of course blanks were always used.
If you are ever fortunate enuff to find yourself out east after DCI Championships try & make it a point to attend the DCA Championships (on Labor Day weekend) as well. It's a great party atmosphere, certainly more of a Drum Corps "family" feel to it & alot of the older traditions can still be picked up on if you know your history, If not, someone there will be MORE than willing & able to offer you a beer in the parking lot, sit ya down & clue you in on your own past. AND the gunshots are still being used there.