What is the best way to measure the bore?

[hrt4me]

My Tingle copy is called a .44 caliber and takes a .433 ball if that's any help to you. Otherwise, I would find a lead ball of about .45 caliber and smack it into the muzzle then take a course wood screw and thread it into the ball and pull it out then measure it.

Unfortunately the copies do not seem quite true to these two originals of mine in terms of caliber; two of mine have rifled barrels which are unmarked (yet both barrel serial numbers match their respective frame serial numbers), however, and so I wonder whether these particular barrels have been spares and/or whether someone other than Tingle made them after the original manufacture...?

All the rear sights differ as well, and those dovetailed adjustable rear sights lead me to believe both those target pistols had been later modified...