Leftoverdj:
Would you also please post specs on ball, chamber, bore diameter, and rifling?
Barrel length: 34-1/8 inch (.87 m), round and tapered
Bore ID: .605 inch
Groove ID: .645 inch groove-to-groove
Number of grooves: 7
Rate of twist: Uniform twist 1 turn in 56 inches
Round Ball OD: .640 inch nominal, 410 grains nominal
Powder charge to fill chamber: 135 grains FFg nominal
Fifty yard groups of 5" x 30" show a major accuracy problem. I would not so quickly assume that a perfect projectile would cure a problem of that order.
You got THAT right! Rendering RBs [nearly] perfect altered groups significantly. Vertical dispersion disappeared. Horizontal dispersion was reduced to about two feet.
If you look at the barrel's specifications, the "why" is clear:
1. For using bullet without cloth/leather patch, rifling is too deep.
2. RBs require very slow rifling for accuracy. With MV between 1780 and 1850 ft/sec, RB is overstabilized with 1:56 twist. When vertical dispersion disappeared using "perfect" RBs, it was a bitch slap.
3. Barrel's specifications are the same as original Fergusons -- except for powder charge. What we didn't take into account were that "accuracy" referred to less precision than what we accept today. And a smaller powder charge reduces MV. Less axial rotation on RB translates into better accuracy, in this case.
We installed a barrel with grooves .005 inch, 1:144 inch twist. This twist had been proven in a muzzle loading rifles of .69-caliber and .65-caliber. Both had been used in Africa, using enormous powder charges. Presto! Accurate rifle. Three MOA to 125 yards. This accuracy doesn't last, though.
This brings me back to what I want for making RBs whose accuracy MAY be better, whose accuracy WILL be maintained longer. And the barrel will be easier to clean after the day's shooting.