We can narrow the date down a little closer; the oval cartouche without a crown is before 1893 and the "not for ball" is after 1875 and I think before 1885. Prior to that date people shot round ball out of their guns, at large game and shot for birds. The not for ball was to indicate the gun was choked. Final point is that to determine what guage the gun is chambered for, you would be best to see what is the biggest guage cartridge will fit in the chamber; I am guessing 12 guage. Length of the chamber is perhaps most easily measured by making a dowel the diameter of the appropriate shell and sliding it into the chamber until it stops without using force. My guess is that it is probably 2 5/8" and was made for roll crimp shells. If so you can use plastic 2 3/4" shells but not paper shells.
finally, if the bores are good and the gun is tight, I would probably put the price at around $250 locally. If you were to remove the locks and compare their inner workings with those of a english gun, you would find them functional but far less finished that the english locks; hence the lower value of the gun
cheers mooncoon