If I had a muzzle loader or reg rifle and 6" was the best it would do it would be staying at home when I went to the woods.Depends on what you want to put into a muzzle loader or even a reg rifle as to what you get out of it.
I for one don't think any of these fellows are lying about their groups,for one reason I have shot a bunch of them and have seen what some of them can do.
Last year I helped a fellow set up his rem muzzie finally after a lot of shooting and several different powders and bullets I wittnessed him shooting a 3-shot one hole group.
Year before I helped 8 fellows set up their new savage muzzleloaders,before we got through,7 of the 8 shot a 3-shot one hole group.Watched one fellow put 7 in a row in one hole.So I know for fact that these fellows weren't lying about their groups.
A few days before muzzleloader season a young fellow came to the range said he wanted to try his muzzie before he went hunting,at 50 yds he was spraying bullets every where,He finally got a couple about 8 in from the bullseye,and said that was good enough.My shooting buddie told him to hold up and volunteered my help.before he left he shot a group about 3 in at 100 yds.
What I am trying to say is I hope there aren't many that settle for 6" groups when I think you can do a lot better with a little know how and enough practice.
I am getting ready to go to the range today soon as it gets daylight,won't be muzzleloaders today mostly varmit rifles.Plenty of all day fun too.