Frustrated

[HighUintas]

Odd man out here I guess....
I'd be pretty happy with that at 100 yards with a flintlock.

How low if a charge have you tried? I have a gun, .615 smoothbore to be clear, that shoots best at 85 grains and down at 65 grains.  You'll get more drop and gave to adjust for it, but maybe a lighter charge would help.

Some time spent at 25 yards and a light charge that groups well at that distance (even if it doesn't group well further out) with just enough prime to do the job might help with the "flinch" and form issue.

I'm ecstatic with that last 80gr group at 100 yards. That's the first time that's happened! I hope that it repeats. I'll be practicing with that and trying some lower loads too. I've done as low as 60gr. I'll try that again and see what it looks like when the flinching is absent

[HighUintas]

A fellow used to come to the Western Nationals who before he browned or blued a barrel, would mount a scope on the barrel by epoxying
 a weaver mount to the barrel. He would mount a scope on it and would work up loads with the scope. He did this in order to minimize sighting errors.
once he settled on a load, he would remove the scope and mount. He had his optimum load at 100 yards.  All he had left to do was to sight in his iron sights with the optimal load. After that any bad shots were attributed to the jerk behind the trigger.

That's a really good idea.

[smylee grouch]

   About     12-15 years ago after I built my hunting cabin I built a 10 foot square shooting deck. I knew that there would be at times some heavy kickers shot from atop of it so I made " stand up shooting benches " on the sides. For right and left handed shooters. It also has a sit down bench for modest kickers. 10x10 is ok for one shooter, cozy for two and crowded for 3 or more.

[Darkhorse]

A fellow used to come to the Western Nationals who before he browned or blued a barrel, would mount a scope on the barrel by epoxying
 a weaver mount to the barrel. He would mount a scope on it and would work up loads with the scope. He did this in order to minimize sighting errors.
once he settled on a load, he would remove the scope and mount. He had his optimum load at 100 yards.  All he had left to do was to sight in his iron sights with the optimal load. After that any bad shots were attributed to the jerk behind the trigger.

A few years ago I made a temporary scope mount that attached with the tang screw and extended forward over the barrel. I prevented side to side movement by making a piece with 2 wings that fit the barrel flats on either side of the top. I only shot a few rounds with it and it seemed to work ok for testing loads but I just couldn't get used to it on my flintlocks so I removed it. I don't have a photo and when the hurricane took the roof of my shop I haven't seen it since, even though I know it's still around.
After that I made simple rear peep sights and that cleared up the rear sight being out of focus. I can shoot almost as accurate with the peep as with a scope.