In 1895, the US Army had the Springfield Armory pull all of the SAAs from storage and shorten the barrels to 5 1/2". They got the name "Artillery Model", but were issued to all units.
Colt started offering 5 1/2 inch barrels as a standard option on the SAA in 1875. The 4 3/4 in 1878. Although people, could and did cut down a longer barrel before then.
