During the late 1890s and early 1900s, several companies in the United States began to develop as integrated ammunition organizations.

One of those was the Western Cartridge Company, which was also a powder manufacturer. In 1892, Franklin W. Olin and his associates formed the Equitable Powder Manufacturing Company at East Alton, Illinois, to manufacture black powder that was sold chiefly to the mines in the area. However, because that business was seasonal, Olin became interested in loading shotshells. In February 1898, he persuaded his associates to join him in forming the Western Cartridge Company, also located in East Alton, the principal purpose being to provide a market for powder that could be produced by The Equitable Powder Company in the off season.

With the outbreak of World War I, interest in negotiating contracts for arms and ammunition picked up sharply. When the United States declared war in 1917, Winchester again was called on to fulfill contracts for arms and ammunition.

The purchase of Winchester by the Olin interests brought a breath of life to the institution. A major benefit was having the leadership of John M. Olin, son of company founder F.W. Olin. When John Olin, at that time First Vice President of Western Cartridge Company, came to New Haven to find out just what he and his associates had purchased, he found stored-up accumulation of new gun models and ideas. He was able to make an accurate appraisal of each model and to introduce a number of revolutionary ideas he had in mind.

John Olin was a master inventor

...and his name appeared on more than 20 patents, several of which dealt with Super-X developments. Super-X ammunition, probably Western Cartridge Company's most widely known product, resulted from his work during World War I. Super-X was a major development in the ammunition industry early in the post-war years. It came, according to John Olin himself, partly from his personal desire to teach sportsmanship to a hunter who shot ducks on the water rather than on the wing. Olin even suggested to the greedy hunter that if he needed meat on the table he should go shoot a cow. "You can get a thousand pounds of meat with one shell."

On December 14, 1940, a contract was signed with the government for the United States Cartridge Company, a subsidiary corporation of the Olin-owned companies, to build and operate the St. Louis Ordnance Plant, the greatest small arms plant in the military history of the nation. At its peak production period in 1943 the plant had 34,338 employees on its payroll. Manufacture of ammunition components began October 20, 1941, and the first finished ammunition came off the line at the new plant on December 8, 1941, the day after the Japanese attack on Pearl Harbor forced the United States into World War II.

Total production of .30 and .50 caliber rifle and machine gun ammunition at the St. Louis Ordnance Plant during the war, 6,738,009,746 loaded rounds, exceeded the output of all of the nation's small arms ammunition plants in World War I. In addition, the Western Cartridge Company plant at East Alton produced 4,022,621,734 loaded rounds of ammunition, and the Winchester plant in New Haven another 4,499,493,774 rounds. Thus a total of 15,260,125,254 rounds of ammunition were produced by the various Olin companies during World War II.