That is an interesting thought on the grip, but I'm not sure how I could prove it. Maybe glue some nitro cards into the wad so there can be no slipping?
These are extreme meplat slugs, but they are a stabile design. They will fly really good from a smooth bore, so spin is not needed but it always helps. I've been shooting these at both 50 and 100 yards with the Benelli. I'm finding if it keyholes, it will do so right out of the muzzle. Why I can't say, but by not using that nitro card it no longer happens. That's all I can say for sure. The ones that fly stabile, seem to be stabile for long range. I'll be doing some 200+ yard shooting at some point this winter to really test them.