The Colt Monitor was Colt’s improved version os the Browning Automatic Rifle intended for the law enforcement market. Colt had the sales rights to the BAR in North and South American (as well as a few other specific countries), and they worked on improving the design after World War One. In 1925 they introduced the R75, which was a military version of the gun with a bipod, pistol grip, dust covers, and a few other improvements. This was joined in 1931 by the R80, a law enforcement version also called the Monitor.
The Monitor featured a shortened (18”) and lightened barrel, no dust covers, a pistol grip, and a large Cutts Compensator muzzle brake. It was targeted at police agencies which had experienced problems with Thompson submachine guns failing to penetrate the heavy steel panels of large automobiles – the .30-06 cartridge had no problem at all dealing with cars in the 1930s.
In 1933 the gun was formally designated the FBI’s official Fighting Rifle, but the agency only purchased about 90 of the guns in total. Another 20 or so were sold to other police agencies, but at $300 (roughly $5500 in 2017 dollars) the Monitor was simply too expensive for most depression-era agencies to justify or afford. Less than 125 were made in total.
This particular example was owned by the late Jim Ballou, author of the Collector Grade book “Rock in a Hard Place” about the BAR, and has a couple non-original markings added by him. It is, however, one of very few fully transferrable Colt Monitors on the NFA registry.