What NOT to do!!

This is a 12ga dbl barreled "Shottie" as SamD calls them. Its an N.R. Davis & Sons, from Davis Warner Arms Corp. A friend of mine wanted me to fix the bore of the barrel, which had a screw protruding about 1/8th of an inch into it, from his Grandfather mounting a scope on it, and then removed it years later, only to plug the "hole" with a stupid screw and not filing it down. I thought, Cool, I can do this!! To my dismay, When I saw it this morning, I almost called this friend of mine right then, to tell him to get this thing off of my property. But instead, I took a few pics of it, got exact measurements on it, then disassembled it, and it is now back with its owner. The barrel is exactly 12 inches long, and the gun as a whole is 18 1/2 inches long. I tried to look this gun up in my Modern Gun Values book, but couldnt find it, so I then had a friend that looked in their Collectors Guide, and He informed me this gun was made sometime between 1853 to 1919. The hammerless, like in the pic goes for $900 in excellent condition for grade A, or $400 for the lesser model. Someone cut up a 100y/o shotgun that could've been worth a lot of money.. Its just a shame!!