Cartridge making also depends upon if one wants to duplicate the original as close as possible or have a cartridge easier to make that has reasonable reliability and accuracy.
Either way, it is time consuming but not overly difficult. After many experiments, I settled on the latter and developed two types based upon Pyrodex pellets and the 405 grain 45/70 HBRN bullet. The pellets help the cartridges to have consistent and repeatable lengths as the powder is already compressed.
Type A can be made without a mandrel as the Pyrodex pellets themselves are taped together to make a form for the paper tube (see photo below). This method requires making a pocket in the base of the first pellet for the musket cap primer assembly. Length is adjusted by the number of wads between the pellets and the bullet. The bullet is retained by tying it to the paper tube by its lowest lube groove. This cartridge ignites the best, but does leave the most residue in the chamber.
Type B uses a mandrel (metal preferred) as the form for rolling and gluing a single layer traditional paper tube. Gluing the musket cap primer assembly to the bottom of the paper tube is facilitated by a pocket in the end of the mandrel. The space around the primer is filled with loose powder and then covered with a thin paper wad. The pellets are dropped down the paper tube on top of the primer assembly. Wads are added as needed between the pellets and bullet to get the needed over-all-length. Bullet is tied as in Type A. This cartridge has slightly less reliable ignition, but leaves much less residue in the chamber while giving a slightly higher velocity.
Besides the seal and needle already mentioned, one also needs to check the needle retainer and its corresponding T on the end of the bolt for any signs of metal fatigue. The design is such that if a failure occurs at this junction, the cocking assembly will be expelled violently rearward into the shooters face. These failures are rare, but one needs to be aware of the possibility.
My Chassepot celebrated its 140th birthday in May of this year and I have no reservations about taking it to the range.