G3-M4 Stock Adapter

thingiverse

Overview: I designed this adapter for my PTR91 after pining over the one at HKParts, I instead designed it in CAD, and my first printing attempts appeared to be strong. I also tried to put a QD cup at the bottom of it. similar to the one from FAB Defense Printing: I printed it out in Esun PLA+ with 100% infill, aligning the flattest face with the bed. you could probably go with less infill, as even the 10% parts seemed relatively strong, so I would recommend 50-100% Testing: It seems quite strong, but the threads were tight for the buffer, and I had to use a vice to tighten the buffer onto it, after getting it onto it it seems extremely sturdy. as for the bolts to attach to the receiver, I believe that they are M5 bolts, but I'm still experimenting, the original stock uses heat inserts in the plastic, and this would most likely be the failure point for this part, as the screws are pretty small, in the end, we ended up using an M6 tap, which was tight on the receiver, but it did work, It tightened up quite well, and it seems like there is only a small bit of flex in the side to side direction. You will need to go out and buy the heat inserts, they are available here https://www.robertrtg.com/store/pc/HK-THREADED-BRASS-INSERT-FOR-PLASTIC-STOCK-p5779.htm Alternate method, I have not tried this, but you could potentially print this out with a small infill amount, fill in and around it with plaster, and cast the part out of aluminum. this would likely be the strongest part, and the most similar to the HKparts one.