Several of the people in my group[our club] did it for several years including me you had to work out a different load to get accuracy my particular load put two 45 cal balls about 1 inch apart. It had some serious knock down power worked well on deer.
THEN one of the guys ended up with a bulged barrel since I had built the rifle and did most of the repair work for the guys we set out to find out what happened. To make a long story short one of the experiments I set up showed that the air trapped between two PBR could push the last one loaded back up the barrel causing an obstruction. We made a rule against shooting them on our range and wrote TC a letter suggesting that with tightly patched balls and a rifled barrel it could be dangerous. Lee