This is my Great X3 grandpa, private donovan during the civil war. That is the extent of my knowledge other than he was a union soldier. I am hoping for maybe information about the gun, uniform, anything my untrained eye would miss. I apologize if this is the wrong subreddit. Wasn't sure where to post.
If you know his full name the Soldiers and Sailors Database may be able to get you his war records. That can tell you what regiment he fought with and from there you can determine what he did.