Defense Distributed have successfully fired over 600 rounds using a 3D printed AR lower after their last attempt failed after firing just 6 shots.
The “lower receiver” is the part of the gun that contains the trigger mechanism and receives the ammunition magazine. Defense Distributed have already designed a 3D printed magazine that holds more bullets than is allowed by gun controls.
After redesigning the AR lower to strengthen it with additional material to relieve stresses two versions of the part were printed using, one printed using SLA (stereolithography) and one using FDM (fused deposition modeling).
During testing the SLA 3D printed part managed to fire over 600 rounds without showing any signs of fatigue or failure. The FMD version only managed 88 rounds before suffering an unrelated failure. The FDM lower was printed using a Dimension SST, and the material was p400 ABS.
The 3D design file is available on DEFCAD for download.