SkyPilot (and any other readers who are interested)... here's a bullet/cartridge ID rule to rememeber.
You see the small disc in the center of the cartridge's base. It contained the primer which ignited the powder in the cartridge. Such cartridges (with the small disc in the center) are called "centerfire primer" cartridges. Absolutely no centerfire cartidges were used by either side in the US civil war. The US Military did not adopt centerfire ammunition until the 1870s.
You might want to pass this information along to your friend who said they are civil war cartridges.