I'm not going to address the leading issue, that has been done.
For accuracy, don't give up on the powders you have.
I would try magnum primers if you haven't already, and using more crimp.
Even a +P load of powder in a 38 Special is going to have a lot of air gap in the case, getting positive ignition is key to getting good performance from any round.
Machine guns are awesome until you have to carry one.