This is the best information I've been able to find online for Mr. Allin:
(Text and images taken from
http://www.nps.gov/spar/learn/historyculture/genius-of-springfield.htm )
"After the Civil War the United States was left with thousands of muzzle-loading percussion muskets. While the barrels of these rifles were perfectly good, technological advance represented by breech-loading rifles firing metallic cartridges, had been put aside while the Nation faced its crisis. With the conclusion of the war the government decided to convert the muzzleloaders into breechloaders. Erskine Allin was one of several individuals who contributed modification designs.
Allin was born February 3, 1809, and began work at the Armory in 1829 as an apprentice in the Water Shops where his father Diah worked as a foreman. He rose through the ranks, and between October 1847 and May 1848 he served as Acting Master Armorer. In 1853 he was appointed permanent Master Armorer.
Allin’s greatest contribution was the development of the 'Trapdoor' breech mechanism which could be adapted to the existing muzzle-loading rifles. In competition his design proved to be the most acceptable*, and he was requested to convert 5,000 M1861 rifle-muskets to use the new breech. These were known as the M1865s. The next year, after improvements were made in the extractor, 25.000 rifle-muskets were ordered altered. The first rifles built from the start as Trapdoors – not converted from earlier muzszle-loaders – were completed in 1873. Allin retired five years later and died on September 11, 1879. In tribute, the Armory shut down on the day of Allin’s funeral. It is estimated that 250 of the 3000 Armory workers attended the funeral, a testimony of the esteem in which he was held."

"As Master Armorer, Erskine Allin indicated his acceptance of a completed rifle by the imprint on the stock of the weapon of an oval cartouche bearing his initials."

"Erskine S. Allin, Master Armorer, Springfield Armory, 1853-1878."
*This is disputed elsewhere, but in one of "those" blogs, so it is not worth mentioning here. However, other repeating rifles quickly overshadowed the M1865.