Back after losing time to a lightning fried computer. Test in 3.5" plastic using a few accutip 12ga sabots out of factory loads. The 12ga accutip sabot, hard cast 440gr 58cal minie slug in 36" rifled NEF at 2200, and it went through 12 inches of wood like butter. The hole out showed it was starting to expand a little. Test of softer lead 500gr 58cal Minie with deeper hollowbase in accutip in smooth cylinder bore barrel at 2000, and 3 shots in 3" at 30 yds. This was a Lyman 575213 new style minie slug More experimenting can make these work fair in smooth barrels. For best accuracy use a blunt nose heavier 58cal 600gr slug with deepest hollow in the base. The blunt nose would be more front end heavy and a little more accurate from smooth bore.. Lee and Lyman have molds like that.Others selling slugs also. I mentioned before about seals/wads must be stable and not crush down off center, or it might affect accuracy. Here is picture of the one piece seal and wad Federal uses in their sabot loads. Notice it doesn't have a lot of space in the cushion part that would allow it to tip or go off center.
Here is picture of some 10ga work using expanded 69cal minie and 700cal bullets in 10ga wadcup. 69cal hollowbase fairly accurate to 50yds in heavy barrel smoothbore.
Here is picture of the Savage 110 done in my 585HE. Hollow butt of the stock is weighted, gun handles nice.Ed