Ed-

This is the business end of one of my two 16 bore double rifles.
The grooves are about .008" deep.
The lands of my other 16b double rifle are a bit narrower.
I've seen very thin lands, I've seen henry rifling, I've seen really deep grooves, I've also seen 'invisible' rifling -- essentially parabolic 'smooth' rifling.
One of my rifles has a roughly 40" twist rate, the other one is slower.
Both of them shoot roundball quite well.


--Tinker