The uniform looks to be that standard 1885 coat, used until 1902. The numbers are not the regulation US Army type, but very common with state troops. So family history prevails.
As for the carbine, he could have been a mounted courier, he could have transferred to a different unit...or (and I hate to do this to people), picked it up at an Ordnance dept sale as he was leaving. I actually know a friend who's ancestor did that. The Army apparently wasn't too worried about retaining trapdoors at that point.
What I am saying (and I hate to burst bubbles) is that more often than not the gun "brought home from the war" is not directly related to the soldier's service...ie, not his ISSUE weapon. These things were serial numbered and accounted for and stealing government property was just a big of a crime back then as it is today and the USA we not in the habit of passing out paid for firearms as gifts to veterans. However, when weapons were obsolete, their sale were authorized (early form of the CMP/DCM programs). Its like my grandfather, got to play with an M1 Carbine is W2 and fell in love with it. As soon as he could after the war he bought one on the civilian market. Some family persisted that it was his military weapon. An older gentleman I knew years ago was a WW1 vet, in 1927 he bought an M1917 rifle from the government through the NRA. So the M1917 in the pictures of him in 1918 and the M1917 the family owns now are not related, but some members of the family persist they are. Family tradition/history is marred by lack of knowledge militarily (I can not tell you how many houses I have been to with Span Am was pictures on the wall being told that is the Civil War vet of the family. Long story short, the person doing the family history found an unidentified picture in the family boxes (and it may have been a picture of a buddy) and deduced it was the Civil War vet based on the military uniform and that became the official family story.
You also see this alot in ACW era. Guns are functional. I love how many Henry and 1863 Remington that belong to confirmed CSA vets and the family insists they carried it a Shiloh or something. Both weapons were VERY common on the civilian market in the 1870's and 1880's, but the collector selling it now insists that it was what he carried in the war even though the guy lived till 1947. So If a CSA vet owned a M1870 Rolling Block upon his death, does that make it a Civil War Relic?
As historians, we must be leery about identifying items because it makes them neater. Or stretching for conclusions that make it a combat item (transferred to a cavalry unit, mounted courier, etc.) with is a less logic conclusion that ordnance sell.
Chris Fischer
F-Troop