John B. fired this volley in
:

Certainly. But when he's got it, what is he going to do with it?

He's going to draw stuff, John! Half the 'fun' of designing a replica of
anything without original prints is trying to draw something that looks
right, then checking the fit of all the things you DO know the dimensions
of.

Since the only dimensions he can get are the cartridge and the bullets, he
starts there. Likely someone knows exactly what round it was chambered
for. Once he knows that, he can certainly come close on what size/weight
of projectile it had.

LLoyd