If you'r gonna try shooting weird projectiles out of a gun, why not use a blunderbuss? After all, wasn't it pretty much loaded with what ever you could fit in it?
No. That "load with what ever you could fit" is a myth. It is probably based on the appearance of the wide belled muzzle. It looks big. The actual bore, however, is a standard gauge, 12 for example.
BBs were most commonly used aboard ships and on stagecoaches.
The function of the belled muzzle was to facilitate reloading while on a moving platform. The standard load was shot. The non-standard load was more shot.
I have a 14 gauge BB with a 14" bbl. It is a hoot to shoot.