A nice Trapdoor, and the date on the breechblock is 1873 and not 1878. Many survived in excellent condition, and in my estimation one of the great bargains in U.S. military rifles. The breechblock and tang were color casehardened, the barrel and receiver rust blued, and the small parts niter blued. I am sure you know the sling is a reproduction.

It shows up in 1898 as being issued to Company M 151st Territorial Volunteer Infantry.