From what I've read, the copper tube (not a bullet jacket) was inserted in the nose of the hollow point bullet & was usually the same size as a .22 Short RF ctg. It was either empty, just a copper tube, covered end or not to slow down the normal expanding rate of the bullet, or was primed and filled with BP or detonating compound for the more explosive type of 'shell'.

Back in 1863, Forsyth wrote and pictured shell moulds and the resulting bullets for bore rifles from 16(or 14) bore and larger.