The vents were added to cap locks because the flintlock people claimed that the flintlock shot harder because of it's more open system because the powder could breath better...thus vents were added to cap locks so they would shoot as hard (it was later found to be hogwash).
I tried every loading combination Starr talked about and had my best results with a thick Nitro card, lubed fiber cushion wad and thin over shot card. The 3 vintage muzzleloading shotguns I had (a 9, 10 and 13 bore) all shot better with full power loads.
I hunt with the guns I own and after realizing that a muzzle loading shotgun is a 30 yard gun I sold all mine and converted to vintage cartridge guns with choke.
So I looked at most of what Starr wrote as hogwash with the exception of jug choking.
