CB is a hold over from the early days of the cartridge...
When it was adopted, it described the type of projectile.
BB and CB rounds used to be very common.
BB stands for bulleted breech. When it started out around 1845, it was nothing more than a primer with a piece of round lead shot stuck in it. No powder. These were extremely popular for parlor shooting in Flobert-type rifles and pistols. In the days before TV, shooting in the house was allowable.
CB means Conical Bullet. The original form combined a heavier bullet shaped bullet with the BB case and a little powder. That kind of CB hasn't been in production in the United States since before WW II.
What we now see today as "CBs" are the lighter bullet in a .22 Short case, usually downloaded so they aren't as loud.
In my Remington 521T target rifle, with Remington CBs, the striker falling is actually louder than the round going off.
