If you think about it, the reason Vinyl has a bass cannon in the first place is because at one point, the military force of Equestria was experimenting with acoustic weaponry. Vinyl got this crazy idea for a design, and made it herself. The result: Her bass cannon, which can easily obliterate gods (like Discord). Unfortunately for Vinyl, the program was scrapped, and it was directly after she used the B.C. in the facility for a demonstration. The only other time she got to use that thing, was the aforementioned obliteration of Discord.