Kelvin simply needs to obtain more documentation on his great-great-grandfather's military service in the Spanish-American War, and then determine whether the Spencer may have been carried by him during the war or was instead perhaps a momento-souvenir brought back from the war? Although many people like to think that the United State military forces had the most up-to-date equipment, what may have been in government stores and what was issued was a huge difference. According to an article published by the New York Times about the readiness of the National Guard in December 1895, just three years before the Span-Am War, reported how the Oregon National Guard was still equipped with antiquated .50 cal Spencer carbines, such that while the article does not constitute a full inventory of military armaments of the various states, it does reveal many of the shortcomings of the various state National Guard regiments that can be determined subsequently served in the Spanish-American War, though there was certainly a great number of units that volunteered for active service but did not serve overseas.
At the same time as my grandfather Eustace McAuley (1879-1939) served in the British Army (in South Africa), 1899-1901, his elder brother (born 1869) served as part of the U.S. occupation force in Havanna, Cuba. His name was William Christopher McAuley of Danvers, Mass., and served as a member of Co. K, 8th Massachusetts Volunteer Infantry. Although I have not determined precisely with what arms his regiment was equipped, the 2nd Massachusetts was still equipped with trapdoor Springfield rifles even when they reportedly went up against superior enemy forces armed with bolt-action Mausers.