philne: I believe the Powerstars are 435 gr. and the PowerPunch are 460.
Saturday I was shooting my UM and found that the Powerstars didn't load well at all in a fouled bore (many/most others I have tried so far loaded quite well). The PowerPunch cconicals slipped in with just thumb pressure, then slid all the way down easily.
Just my opinion, but I'd start with some of the lighter bullets for sighting in before going to the heavier stuff. I know they were "free" with your UM, but they're pretty big chunks of lead to be sighting in with (in my opinion).
My best load for accuracy Saturday was the 300 gr XTP (.44 cal) with the green Hornady sabots ahead of 85 gr T7. Just over 1/12" at 100 yds. Are yours .44 or .45 cal? I don't want to cause you to spend any more money (yet), but I think just about any sabot made for your bullet will work in your UM (except for the very thin ones - they'll probably fall back out).

Good Luck and Have Fun!
IM jaybe