If you have access to a drill press, you can build an AR-15 without undergoing a background check. Just buy an 80% lower and a jig. You can order these things o

If you have access to a drill press, you can build an AR-15 without undergoing a background check. Just buy an 80% lower and a jig. You can order these things online. An 80% complete lower receiver is completely legal for anyone to own. In the eyes of the law, it is a chunk of metal. Once you put it in a jig and drill out a couple of parts, it becomes an AR-15 lower receiver. Now it's a firearm. The rest of the parts (upper receiver, lower parts kit, stock, sights, etc) are completely legal for anyone to own without a background check. You can order these parts online as well. Total cost will be somewhere between $700 and $2,000, depending on how fancy you want to get. Actually doing this may or may not be legal. It depends on your criminal record, mental health, the combination of parts you assemble, and where you live. There are a ton of laws related to firearm ownership, transportation, and manufacture. Even summarizing them would triple the length of this comment. My point is that building dangerous weapons is already not particularly difficult, time-consuming, or expensive. 3D printers will make it a little easier, but not drastically so. Different parts of the firearm require different materials. The lower receiver can be aluminum, but the barrel has to be steel. The recoil buffer won't work if it's too heavy, so it has to be aluminum. But it also has to have plastic caps to avoid damaging the buffer tube. Even if you could print these parts out with the right tolerances, you'd still have to assemble them with special tools. If it's so easy to build an AR-15, why don't we see a ton of killings with them? Simply put: because most people are sane. The vast majority of the population, given the chance, would not want to kill innocent people and spend life in prison.