 
                     
                This is an RPD lower I designed a few years ago (drawing is in imperial units, not metric) that uses an AR15 fire control group and buffer tube. A collapsing recoil spring assembly must be made in order to get full travel from the RPD bolt carrier. 
Hopefully this gives someone the start they need to make a super safe RPD. 
 
                     
                    
                     
                FreeMenDontAsk AR-15 22lr Lower Receiver
 
                     
                    
                     
                Superstar-15 3D Printable Lower Receiver
 
                     
                GC1522v2.1.1 - An upgraded Smith & Wesson 15-22 lower receiver
 
                     
                 
                            
                         
                            
                         
                            
                        