We all have our favorite ways of holding a mandrel or not usinig one at all and each of us considers our way to be the answer to all problems mandrel or mandrel-less. For me, I believe the best way to hold a mandrel is to use a collet chuck...not a MT2 one but one that screws onto the lathe's nose. One option is the Beall Collet chuck with other options available from most of our suppliers. Do some investigating and make your choice. I still use a mandrel with the Beall collet chuck and turn one barrel at a time and do not find making one barrel at a time to be any longer than having both of them on the mandrel. Good luck.
Do a good turn daily!
Don