1) Casting is just not "grabbing" me, but maybe when I'm retired in another 30-35 years!
2) When I do, I'll be swaging spent .40cal brass in to rhino-killin' .327 slugs! (inside joke)
3) In all seriousness -- if you are casting your .327 slugs, I'm still going to win the argument. You may be using a lighter slug in .327 than you would in .357, but the "savings" would be miniscule... whereas, the .357 Magnum brass is still incredibly plentiful while the .327 brass is extremely difficult to find. Because afterall... if you are casting your .327 slugs, then you are casting your .357 slugs. The saving in lead & powder aren't going to make up the difference in getting a hold of the brass.