Wrong theatre of the war. the 51st Illinois was not @ Sharpsburg (Antietam) Maryland, Sept. 17, 1862.
See George's response. It appears the two campaigns they were involved in at the time of Lieut. Sweeney's
1862 service were New Madrid / Island No. 10 in Feb.-Apr. 1862; and Siege of Corinth, MS in Apr.-May 1862.