A very enlightening reply, Peter! The professional version of what I have been doing up to now for old percussion revolvers - i.e. sliding a close fitting rod down the barrel and seeing if it reached the end of the chamber without snagging. If it does not touch the sides of the chamber, then the next refinement is to see if the cylinder can be revolved equal amounts clockwise and anticlockwise. Yes, it's a quick and dirty method, but suffices to distinguish between "hopeful" and "hopeless" cases.