The M. S. Little company with it's sub-contractors, the Risdon Mfg. Co. and Scovill Mfg. Co. were the prime magazine suppliers throughout the war. The General Shaver Co. produced field replacement magazines, and at the very end of production some of the General Shaver magazines were used in Remington Rand production.
In your Remington Rand, April/May 1944 production, an L, S, or R marked magazine would be correct.