Here’s a site for starters:

Guerrilla Warfare in Civil War Missouri, Volume IV, September 1864–June 1865
By Bruce Nichols page 384 note No. 39

https://books.google.com/books?id=qURXAwAAQBAJ&pg=PA384&lpg=PA384&dq=civil+war+soldier++Hugh+Masterson&source=bl&ots=jJKvfeOrZC&sig=5yswwgLYOvapdXnU2vC6tBuH2Hk&hl=en&sa=X&ved=0ahUKEwjhj4nCgPbUAhVi4IMKHc-aDxYQ6AEIVTAM#v=onepage&q=civil%20war%20soldier%20%20Hugh%20Masterson&f=false