Normally we think of center fire as requiring fixed self contained ammunition. But through out history there have been guns that use centerfire ignition that do not use self contained ammunition. For instance Harry Popes centerfire muzzleloading rifles, or the in-line muzzleloaders that use a primed 25acp case to ignite the powder. In the 1880's, many target shooters would push the bullet into the rifling ahead of the chamber and then load a centerfire cartridge full of powder.
W W Greener, in his book the Gun and its Development indicates that the first central fire guns came about in the 1830's using combustible cartridges, such as the Dryse needle gun.
So it seems safe to say that not all center fire ignited guns use fixed ammo.
Remington, Winchester, UMC and Goldmark all labeled their percussion caps as "CENTER FIRE" Even the Meacham Arms cat of 1896 offerred UMC No 10 caps and denoted them as central fire.
Does any one know why they labeled the percussion caps as centerfire. Does anyone have a citation to a gun expert explanation why they were considered centerfire?