I would suggest that you patch your bullet .001 to .002 under bore diameter for your slug gun unless you wipe good after every shot then I would patch it to .002 over bore diameter, but only with a harder alloy or you will deform the bullet nose.
If you patch that bullet at groove diameter or patch it to tight you will damage that patch and the accuracy will not be there.
At .001-.002 under bore diameter that bullet will obtrude and fill the groove.
If your using a barrel with deep groover (some are .010 deep) they will not work to good with a PP you will get bad gas cuts.
I would not lube the patch, there is to much of a chance the patch will stay with the bullet and you will get some wild flyers.
Pick out your paper you want to use on the bullet then get a mould with the proper diameter bullet.
Make sure your ML has a fast twist and not a twist made for a round ball. Round ball twists run in the neighbor hood 1 in 60-72 and those will stabilize a long bullet.