A pretty simple build compared to other designs, but it was still an interesting process.



I ordered the parts kit from HKParts, and a receiver from DefGunz on GB. The process requires a special reaction rod and an offset receiver wrench that run a few hundred dollars, but I was able to rent a set from a fellow on Reddit.

When I was tightening the barrel nut, the barrel slipped in the receiver and was a few degrees off and had gotten jammed up in the receiver against the alignment pin.


I hemmed and hawed for a while about how to go about fixing it. After a couple weeks, I decided to just bang it back out of the receiver and try again. Either its stuck like this forever, useless, or I break it while removing the barrel and it's useless. I bought a brass rod and used my trusty hammer, which worked!


I was then able to re-set the barrel and got it properly installed. The barrel nut had to be torqued to 65 ft lbs!!! A scary proposition with a polymer receiver.


After that mess, the rest of the build was a piece of cake. I got it put all together, and then it was time for test firing. The idea of a rifle cartridge going off in a plastic gun I put together myself was daunting, so I stuck a laser sight on it and held it at arms length away, LOL!


It shot well, its a real flashbang generator. After a couple hundred rounds and I was fairly certain it was unlikely to blow up in my face if it hadn't already, I went ahead and filed an eForm 1. And it came back approved the very next day!


Once that was done, I decided the absolutely god awful iron sights had to go. So this is how she sits!