Carl,
If all you had was a curved chisel on a long rod, and a hammer, you Worked way harder than we did. The work actually went fairly smoothly, unless we had a jam. The bit was harder than the degraded cast iron bore, so you had to go slow, lots of water and rotation by hand - well, by pipe wrench. If she jammed, then we had a slide hammer arrangement on the shaft to back her out. We, the Lab, have cleaned and conserved 28 cannon since 1996, from a wrought iron verso (1686), bronze 4 pdr's, 18 pdr long guns (1812), etc.
The picture of the shell down the barrel was easy to take, a good flashlight and a digital camera. There are problems with digital cameras, one takes too many images - where do you store them All, and the mechanical shutters wear out. We have sent two high end Canon cameras back under warranty, and they replaced them for free. One had ~ 136K and the other 86K of images. The good thing is that one knows you have / or have not taken the necessary photo’s. Whatever you do, if you buy a good high end camera, get the extended warranty.
Jim J.