Here are some Semi-Auto rifles for the Union Army during the SGW.
Springfield M1940
A Harrington and Richardson built M1940 from December of 1940.
Designed by Dieudonne Saive, a Belgian emigre to the United States working for Springfield Armory. The M1940 was a result of years of research and development for a new self-loading rifle for the US Military (working the design as early as 1928.) The US Army and Marine Corps were the main users of this weapon, with 961,000 rifles planned to be in US Military Inventory by 1944 in the hands of frontline troops. By the time of Operation Blackbeard however, only 92,000 rifles were in the field, and up to that time, the manufacturers of the rifle were Springfield, Harrington and Richardson, Rock Island Arsenal, Savage, Remington, and Winchester Companies. At the start of 1942, Savage and Harrington and Richardson were only companies making the M1940 as the others were prioritized in making other small arms (such as the older M1903 rifles and the Thompson SMG.) Then in June of 1942, the H&R Company was then ordered by the Union Government to prioritize in manufacturing the BAR rifle and M1919 machine-guns. Savage would continue to the manufacture the model until August of 1948, which the final production figure was around 387,000 rifles. During the SGW, the main operators of the M1940 rifle was the US Marine Corps, US Army Rangers, Squad Marksman, and other select units of the Army. The M1940 would soldier on as a Battle Rifle until the late 1950s when it was replaced by the M1955 Battle Rifle (which coincidentally, was designed by Saive on a modified M1940 system.) As a Designated Marksman's Rifle, it would remain in use for much longer until the early 1990s when replaced by the DMR versions of the M1955.
A September of 1942 Savage manufacture M1940 DMR.
Johnston M1941
A Springfield manufacture M1941 rifle from June of 1943.
A pet project by an engineer named Melvin Johnston, the M1941 Rifle was adopted by the US Military both as a response to the Confederate Tredegar M1937 and as a cheaper alternative to the more expensive Springfield M1940 rifle. The rifle had the advantage of being simpler to manufacture and can be broken down to easier transport. The rifle was built by the Johnson Automatic, Springfield, and Saginaw Companies between March of 1942 and July of 1944 with a total of 533,000 units being built. The gun would be used by the US Marine Corps, US Army Rangers, the Paratroopers, and the US Army. The M1941 would be used by the US Military until being replaced from Frontline use by the M1955 rifle, and would be in War Emergency Storage until either being surplussed off in the 1960s or being given to US Allies such as Liberia, China, Afghanistan, and Alyaska and even a few being sold to US Law Enforcement in which they were used as late as the 1990s.
Fusil à Chargement Automatique Modele 1936
A 1942 manufacture Mle 1936 rifle that was under contract for the US Government.
Designed by Quebecois Gun Designer named John Garand, the Mle 1936 was originally built for the Quebecois Army. In March of 1942, the US Government (who was in a desperate need for semi-automatic rifles), turned to the Quebecois Government for the Mle 1936. In which the local government would accept the order to 35,000 rifles for 3 Million USD. This order would be fulfilled by September of that year and followed up by another order for 20,000 rifles in December of 1942 and then by 25,000 in July of 1943. The total number of Mle 1936 rifles made for the US Government was 80,000 guns, which unlike the Johnston and M1940 rifles, were almost exclusively issued out to Front-line troops of the US Army. The Union Troops who used the rifle would have a liking to the rifle, with one remark by an anonymous veteran "This Quebecois Rifle is for sure way better than the old Springfields that we have been using." Following war's end, a majority of the Mle 1936 rifles in Union Inventory were either put into storage or were given to the new Texan Army. The model would be ultimately be retired in 1957 from US Military service by the Springfield M1955 Battle Rifle.