I've read a lot of stuff about how the best (most accurate) bullet for a cap and ball revolver is a ball not a conical. Also why is this? I understand it can be difficult or more difficult to seat a conical properly but is there some other reason? If this is true for a C&B why not for other ML rifles?
Pistol target shooting usually does use ammunition loaded to lower velocities for best accuracy. So maybe part of it is that the round sphere is the more efficient design for lower velocity shooting.
But that's not to say with absolute certainty that the round ball will always be the most accurate when fired from a C&B.
The problem would be how to measure the accuracy while eliminating all of the human variables during testing.
I'm sure that you know that it would involve using a machine rest, perfectly identical bullets, powder & compression, environmental conditions, cleaning regimen, barrel temperature etc....
However, there may be some revolvers that do shoot conicals better than round balls.
One of our members Voodoochile described how he modified and enlarged the chamber diameter of one if his C&B's to become most accurate with conicals.
And then there's the report about the Clements Custom Guns .50 caliber conversion of the Ruger OA that is said to shoot custom conicals slightly more accurately than round balls. However going back to the opening statement, the higher velocity is not what most folks would consider to be target velocity, and it's not an average C&B revolver either.
So far accuracy testing has turned in several 25 yard groups under 1.5" with both conical bullets and round balls. The bullet has a slight accuracy advantage with the loads I tested. Thus far the best 25 yard group has been just under .70" with the bullet.
http://www.imageevent.com/fiveshooter/ccgoa
They fell with metronomic consistency into 1.5" and under. The best group so far measures just a bit under 70 - caliber center to center with the 250-grain bullet load. The overall impression is that this load has a slight accuracy edge over the swaged round ball.
http://www.gunblast.com/Cumpston_ClementsFugett.htm
Here's an impressive group fired by mec with Buffalo Revolver Bullets: