Plenty can be cooked and there are different ways you can get them to fit inside of smoker barrels.  A good thing is that a lot of  meat fits inside them depending on how you do it.  You can lay them flat on the grate, use a rib rack system to stand them up sideways, or hook hang them using a rib hanger.  Smoke 3 or 4 racks for a competition, 1 or 2 for a family meal, or load it up for a larger crowd using a rib rack or hanger utilizing the full space available.  From 3 or 4 to 16+……it all depends.  More about how many ribs a smoker barrel can cook.