ORIGINAL: AJ52

buck,
I have 2 Mossberg 500's. 1 smooth bore,1 rifled. I've farted around for years with various slugs. I always went back to Federal rifled slugs and sabots in the rifled barrel. They've given me the best pattern out to 100 yrds+. Thats good news as there cheap and get the job done.
But as already stated every barrel is different. I would start out with couple boxes of cheap 2-3/4" sabots and work up from there. If your lucky you'll find a winner in your 1st 2 boxes. Getting a slug slinger where you want it can be expensive!

I found out the hard way yrs ago if your sighting in with sabots swab/clean that barrel every 4-5 shots to get plastic residue out. I have a new 870 that gets real crazy about a dirty barrel (plastic residue).

Also let the barrel cool off. A clean cool barrel will duplicate your actual hunting conditions.

Good Luck