Not to split hairs (which I hate when others do it on the FR) but Civil War infantry didn’t, as a rule, carry muskets; they had rifles. This fact revolutionized warfare and increased the lethality of the conflict. The difference is a rifled barrel vs. a smooth bore, and greatly impacts effective range and accuracy.
“Civil War infantry didn’t, as a rule, carry muskets; they had rifles.”
For the first two years of the war, both sides were equipped mainly with 69 caliber smooth bore weapons. Either 1842 pattern or 1816 pattern converted to percussion. As late as 1864 some union units still carried the 69 caliber weapons.
In the Confederate army some units surrendered at Appomattox were carried smoothbores 69s.