According to Indiana Civil War Records David Copson enlisted as a musician in Company C, 22nd Ind. Infantry Regiment from Brown County, Ind.
I could not find him in 1860 US Census
David applied for a pension in July 1890 while living in Nebraska (application #840186/certificate #614662).
I can not read the day of the month.
His pension index card also lists service (no dates given) as a musician in U. S. Army which I believe was post-Civil War service and may explain why he was at Omaha as the Omaha Barracks was headquarters for the Department of the Platte
You can order his service record and/or pension file through the link at that the top of this website.
The 1890 US Veterans Census lists him at Omaha and slightly deaf

There is a David Copson (c.1840 born in Massachusetts-Feb. 22, 1916 died) buried in the Marion, Ind. National Cemetery. He is listed as a musician, infantry.