[BlueTrain]

Just like rifles today, Civil War rifled muskets were probably capable of better accuracy than those who were shooting them. But there are several points to be made here.

For one thing, you probably remember that black powder was being used and after a couple of volleys, the battlefield was a smokey place. That had been true earlier as well, during the Revolution and the Napoleonic wars. Another possibly more important things was that these were mostly all single shot muzzleloaders. That didn't affect accuracy but in some (but not all) cases the matter was decided face to face. By that time, however, casualties would have already been high and such conditions are not conducive to steady shooting and they still aren't.

All those heavy bullet rifles of the 19th century had fairly good range but did have a lot of drop. The .45-70 from that period, still somewhat popular in some quarters, still exhibits the same characteristics. But firing for the infantry was by volley (everyone in the rank firing at once), which helps hit probability (I expect). Some use was made of aiming stakes later in the century, which is something done to roughly establish known distances on the battlefield but it requires that you stay in one place and hope the enemy comes the way you expect. Rifles later on had very high sight settings, perhaps a little optimistic sometimes.

Finally, generals in the Civil War had in many cases cut their teeth, so to speak, in the Mexican War and had been reading books written earlier that did not take into account the increased accuracy and therefore the effectiveness of rifled muskets. Casualties were terrible, even to include horses.