Its my understanding that in NJ you may not manufacture a firearm without license to do so, even for personal ownership.  It was also my understanding that someone who legally manufactured a NJ legal firearm in another jurisdiction for their own nontransferable ownership and then brought that firearm into there NJ residence (serialized or not) was not in violation of any NJ laws. In this video murphy states "anyone caught possessing a homemade or 3D printed firearm .......... will be p