Hi all, just a few quick questions

Recently aquired some superfields to try, they work great in my vulcan but are rubbish in my S10. I was wondering what the little dimple is, as it doesnt really look like a proper hollow point. And why does it have a band around the head of the pellet?

Also why do barrels seem to vary so much? Surely with modern production methods etc they should be accurately made to the same size... yet some guns shoot 5.51 or 5.52 or 5.53 pellets better than other sizes??

Cheers in advance and happy xmas to all