Nothing complicated about it, just remove the bbls. from the gun and then holding them suspended from the lump with your index finger then give them a light tap along the outer portion of one of the tubes with something like a pocket pen; if the bbls are sound they will 'ring'.
note: you may find it easier to suspend the bbls from a closed loop of nylon cord like that used for starter rope for small engines. You do not want to use something that might break or that would mark the lump. A small tied off loop of 6~10" diameter is quite sufficient for the purpose and will pack easily for the average gun show isle foray or gun shop visit.
I wish to say that it was Dr. Oscar Gaddy who first mentiomed the methodology here on the board, but may be mistaken on that point. It does work!
