You guessed it

This is an m1919a4 - the primary U.S. light machine gun of WWII.
These kits have been sold for years with the right side plate removed. These "parts kits" are useless as-is but can be rebuilt easily using a newly manufactured right side plate. The simplest reassembly would however return it to a full auto gun - illegal in all states since 1934 unless you have your class III license, which is another whole story/rant I'll get to later.
There are ATF-approved ways to reassemble this gun into a semi auto which is legal. These mods usually cost about $500 or a lot of work and machine tool experience. Funny, for about $5 in steel plate and several hours with a drill and a file you can have an illegal machine gun. For $500 in parts/machine work and the same assembly work you can have a legal gun. What message does our government really send? Actually, it is sending the right one - people will obey the law or they won't - irrespective of the availability of weapons! If they can make a gun in prison, and they do, they can make one anywhere with anything.
Overall, doing the right thing has never been the easy way out so since I don't fancy a pricey fine and the removal of all my legal toys, or worse, a prison term, I'll comply and do things as I usually do - legally - the hard way!

BTW, if you Brady Bill types can show me one instance where a "gangsta" was smart enough to rebuild one of these and use it in a crime, I will eat it piece by piece!
Don't forget, I owe you a rant!
Love,
Me