What is the title of the 1861 manual to which you are referring, Dan? I have have several with that publication date. Since most manuals of that date make only passing mention of rifled projectiles (if any) I can only assume that the mention of tow would be refering to the cartridge bag still being seperate with no sabot being used. You can't tie a bag to a round ball with no sabot. However, in the case of seperate cartridges, the preferred method was to close the forward end with a wood cartridge block. Cartridge bags themselves were made of close woven wool and of only two pieces: a circular pices for the bottom and a rectangular piece for the end. I make no claim to expertise on Confederate ordnance. During my career, it was the one field of ordnance I never worked in. McKee & Mason seem to think it was for tying on a cartridge bag, and since it is wood, this in engineeringly feasible. Of course, Mckee & Mason also show Archer type projectiles having a wooden sabot covered with metal that covered the entire base of the projectile and would preclude the knob on the base from being used for anything including tying on a cartridge bag.