Someday I'm going to figure out a way to save my answer and others to this question so it is easier to reply to.
Two different 20 gauge guns, both like different loads. (In other words you will still need to do some range work to figure out what is best for your gun)
1st, a note on smoothbore load development, well,,,, Two notes.
1. I'm not an expert or master, I don't compete, I hunt and shoot to practice for hunting, my standards are fairly high though, beware those that give load advice and say "it works good enough for me," without defining what their goals are. I want 4" or less at 50 yards, and really expect more like 3" or less.
2nd. Maybe more important than the 1st note. Discard all conventional wisdom regarding rifle load development,,,,,, but not logic and reason.
Tighter is not always better with a smoothbore is the biggest one.
The less seal you have, generally the more powder you will need,,,,, generally. There are folks who shoot with no patch or wads, just ball on powder. But, I'm not sure of their accuracy standards, this leads to a lot of fouling, and, they usually are using large powder charges.
Gun #1. TVM Early Virginia Smoothrifle.
Likes: in order; 85 grains 3f, thin overshot card, lubed felt wad, .610 ball, two thin overshot cards.
I arrived here when tight patched loads at any powder charge did not work,,,, but,,, reading about people having better success with just wads and patches, I tried a loose patch and ball,,,, .595 ball and .010 patch with a thin card to separate the lubed patch from the powder.... Instant improvement. So, I tried the wads and after playing a bit with powder charges and number of cards and felt wads arrived at the above load.
Then, I became interested in shooting a woodswalk at a club that doesn't allow a powder charge that heavy. This is where this gun's second good load came to be. I played around a lot, basing what I was doing on the loose patch/ball round improving things.
So defied conventional wisdom again and dropped my charge much lower than the club's maximum.
Turns out, in this gun, 65 grains 3f will shoot a .595/.010 ball/patch combo as well as the above load with wads, as well as shooting a paper cartridge wrapped ball pretty well, and a card/wad/.595 ball/card load decently.
Gun #2
None of this works up to the same standards in my Centermark Fusil des Chase.
It shoots 80 grains powder and a patched .600 ball pretty darn well. But, this kicks pretty hard (since being ill and loosing quite a bit of weight/muscle a couple years ago I don't handle recoil like I used to) at least off the bench, might be fine in field positions. Also, and I know it doesn't matter to many folks but it does to me, a patched ball in this gun would not seem to be historically correct for my time and place of interest.
I'm still working on loads for this gun. The one thing I've determined that seems certain, it does not like anything stiff behind the ball,,,, no overshot cards.
Right now 75 grains 3f, dry felt wad, lubed wad of either felt or "tow", .610 ball, thin card, shoots best, but I think could be improved.
I'm also playing with 2f loads to change the pressure curve and spike in hopes of changing recoil and group size.
I hope this helps someone.. I apologize for the length.
