Another contract was awarded on January 31, 1942 to a company who stamped some of their magazines with the letter code SWCO. The contract was to Sparks-Withington for 1,300,000 twenty-round magazines for a cost of 34 cents each on U.S. Government P.O. # 1265. This company produced three different versions.

The first version was blank with no markings on the outside of the magazine body. However, there is a circle mark on the inside of the backstrap of the magazine. The other distinctive features of these magazines are the drain holes are only .140 inches from the back of the magazines. On all other box magazines the holes are .270 inches  approximately from the back of the magazine. Also, the follower's magazine trip slot is .330 inches wide verses .375 inches typical.

The second version has the SWCO. markings on the front face and the a circle on the inside of the backstrap. The drain holes are also .140 inches from the back and the slot is .330 inches wide.

The third version has the markings on the front face changed to SW-CO.

The Seymour Products Company of Seymour, Connecticut was also given a contract on January 31, 1942 for the production of 2,835,400 twenty-round magazines at 28 cents each on P.O. # 1260. Seymour's production ended in November 1942. Only one style of twenty-round magazine has been noticed.