The Soviet standard light machine gun, the DP/DPM, was getting obsolete by the end of World War II. A mobile belt-fed gun was needed, and so the DP was adapted to that purpose. A top cover was designed that replaced the standard pan magazine and fed from existing Goryunov belts. The DP has a sturdy reciprocating charging handle, and the RP46 top cover hooked over this, and used it cycle the belt mechanism.
Because the top cover hooked into the existing front and rear magazine catches, a slot was added to the rear end of the barrel shroud which was engaged by the RP46 carry handle. This way, the weight of the gun when being carried was not supported by the mag catch. The conversion was backwards-compatible with existing pan magazines – the top cover could be removed just like a magazine.
We have a number of photos of a top cover in the RP46 page of the Vault, as well as an original Russian RP-46 manual (also available on the Original Manuals page). In addition, we will be producing reproduction RP46 top covers for sale in the future – a very cool accessory for you live papered DP or one of the semiauto builds that are available.