I would bet on the muzzle damage. Theoretically one of the advantages of the Deeley and Edge action over the Martini is the ability to be cleaned from the breech. Muzzle damage from cleaning should be minimal, but then who knows what adventures and abuse this pretty old gal has enjoyed in the last century and a bit.

I am surprised that the dealer is so far off in his description. I would bet a chamber cast looks a heck of lot more like 500/450 No.2 musket than any nitro express cartridge.