doublegunshop.com - home Forums General Discussion Double Rifles, Paradox Guns & Gauge Rifles @ doublegunshop.com Sub'ing Round ball in shot load recipe/ PSI wise?

Hi lads..I guess the real answer is sending 5 rounds to Tom Ambrust(sic?)for testing.
But before I do....
I have a H & R ugly duckling Slug Hunter Single 20 bore with rifled bbl..I have made up some light loads with a custom ball mold,it shoots amazingly well i think...with scope it'll do 1 1/2" all day @ 50 yds .
Just wondering if I use a shot recipe of equal weight..or slightly more rather than less, to be safe,than my roundball...do you think Psi would be less or more when subbing the roundball..???
Rifling friction.....V wad friction.
If I ever find a nice reasonable vintage single that's suitable , I think this H&R bbl would be a fine one to use for sleeving ,once you knocked of the bits that are in the way.
Any opinions
Cheers
Franc