Far be it for me to be an expert but I did use drillings when hunting in Germany in the early 80's. As Tom H has mentioned they are not ideally balanced as a shotgun but the shot barrels are usually used for small ground animals, foxes, badgers, hares, etc. and roosting birds or those on the ground, crow, black cock and capercaillie, not so much for flying birds.
That is how I saw drillings used and used them myself, got a couple of Roe deer one morning with a 16G/16G/7x65R drilling.