"#2..I started this thread because of the thread on here about the Husqvarna RB that has a bore of .622 and a groove of .662. WOW that's .020 deep rifling! This person is experimenting with .662 balls and slugs in his 20 bore ...Why were these bore guns rifled so deep and do I need to do the same?
I believe that in BPCR rifles the bullet needs to be .001 over groove dia. does this apply to bore guns too?... "

I have one of the Husky Number 4 20 Gauge rifles mentioned in that thread and use the .662 round ball over just 70 gr. FFG, nitro card, 3/8" fiber wad, and a dollop of Bore Butter. That seems to be near the original .42mm brass case loads for that particular gun.