One of Melvin Johnson’s early prototype rifles, made in 1938 by the Taft-Pierce company of Woonsocket, RI. Note the detachable box magazine. Johnson dropped this magazine design in an effort to prevent fraud, as he believed US Army testers were deliberately re-using bad magazines to induce malfunctions in his rifles. Image source: milpas. 
. Johnson vertical magazine M1941 
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. The Johnson Automatics, Part II: The Johnson Light Machine Gun - Small Arms Review. 
. The Johnson Automatics Part I: The M1941 Semi-Automatic Rifle - Small Arms Review 
Melvin Johnson semi-auto 30.06 Taft Pearce prototype B6680 - The Firing Line Forums