OP, you're onto something.
Lead after jackets. Jacketed bullets leave small traces of copper on the bore. Lead seems to stick better on copper than on steel. Or at least that's what some guys on the cast boolits site swear to have happened.
I didn't notice any issues. But then again, I didn't pay close attention.
Jacketed after lead... done this quite often to clean the leading (but the leading was really thin). Again, cast boolits pundits say the jacketed bullet might "surf" over the lead deposits rather than pushing them out. In this case you get a ringed barrel.
Try both using your common sense.
And don't forget, there are gas checked and semi jacketed bullets that combine lead and jacket.