You are right, there seem to have been no shortage of type 3 cleaners in the Atlanta Campaign. One interesting thing I noticed when digging Ezra Church, was the amount of cleaner stems that were around. It seems like they were pulling the stems out before loading the gun. I have heard that the soldiers weren't too fond of the cleaner bullets as they would tend to get stuck in a highly fouled barrel. My theory was that they perhaps started running low on ammo and the cleaners were the last bullets used so they pulled the stems off and loaded them like a conventional round.
D.