It would seem to me the main concern here would be from the uneven heating of the bbls if one bbl only were fired continously in a rapid sequence, such as trap singles. Whether or not doing this frequently would put enough strain on the solder joints binding the ribs to the bbls to eventually loosen them I simply don't know.

In most game situations if birds were flying over in such rapid succession it would simply seem prudent to fire both bbls before reloading.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra