I have seen barrels that rang nicely with perfect looking ribs that still failed the hot water test.
I hold the barrels from the breech end at a slight muzzle down angle and pour very hot water over them.
Give it a few seconds for the air to heat up between the ribs and look for any "fizzing" along either side of the rib.
This does not nesessarily mean the rib is loose, but does indicate missing or unattached solder.

GDU