Ian has a great video post at GunLab on how what looked like a simple project to make a simple add-on, one that has already been proven and manufactured in large quantities in at least two countries, can be hard to do. What looks like a simple piece can be a challenge for CNC machining, when it was designed for the machine tools and manufacturing processes of another day.
The RP-46 Company Machine Gun (Russian, transliterated: Rotny Pulemyot) is essentially a DPM light machine gun with a belt feed grafted on, which gave the 1920s design another thirty years of life.
With the proliferation of semi-auto DPs and DPMs, it seemed like a conversion kit would be easy enough to do. The parts illustrated here are from an original RP-46 examined in a post at Ian’s other website, Forgotten Weapons.
As is common with his posts (and increasingly, ours, for which we are most grateful) one can learn a lot from the comments, also.