The top or bottom ribs on a double gun can
become loose. The solder holding the ribs to the barrels
can get hot from rapid shooting, especially using black powder,
and the solder can fail. Or, a manufacturing process may
not have solidly bonded and vibration could cause the solder
joint to fail. In any case, the problem needs attended to.
A simple and well known test for loose ribs
can be preformed with the barrels separated from the action and
forend. Let the barrels hang from your index finger by
placing the hook (the part that pivots the barrels from the frame
when they are opened) and then tapping the barrels with a flick
of a finger nail or some other semi-hard implement. Care
should be taken not to drop the barrels and avoid the use of an
implement that could scratch or otherwise damage the barrels.
If the ribs are loose, the sound made by the
barrels will be a dull "thud". If the ribs are
tight and the barrels are in good condition, they will ring like
a bell. If you don't hear them ring, have a qualified
gunsmith evaluate them to determine their true condition.
And here is a tip for checking for loose
ribs. Put some oil in the cracks of the ribs, where it meets the
barrels, and let it sit for a minute. Wipe the oil away and then
under a good light, push down and squeeze on the rib
firmly. If it is loose, you will see oil movement as it pushes
out from under the rib.