I think you missed the argument Flipside, Blackwolf. It's not that this could end up being some type of attributable weapon - it totally could be.
The argument we've made is thus: A 3D printed gun will, for the indefinite future, be less effective than either a true - purpose manufactured firearm, or garage made zip gun.
You guys are coming at this from the wrong perspective. First, while in America it's very easy to get a gun but that is not true in most of the rest of the western world. The existence of downloadable 3D printed weapons will be a big factor in places where guns are currently effectively controlled and are hard to get hold of.
You say that this applies only in the US, that in places where firearm control exists. This doesn't at all take into account the fact that black market cottage manufacturing of firearms is pretty much a widespread phenomenon. This is the limitation of gun control - you can't stop people from throwing them together. The barrier of entry is not high at all.
Secondly, everyone going on about the fact that you can make guns at home from parts is fundamentally missing the significance of a 3D printer. This is a device that will almost inevitably become more complex, more capable and cheaper with time. There will come a day - and not one too far into the future I suspect - where a common household device that will cost less than a couple of thousand dollars (on par with a decent washing machine or dishwasher or refrigerator) will be able to produce complex, multi-part objects utilizing a number of different input materials and production processing. We have the capability now, it's just a matter of integrating multiple devices into one and mass producing them. The demand will be huge, so the supply is inevitable. That lowers the barrier of entry far, far more than you think.
I'm not sure how sophisticated you think 3D printing will be in the near future - but I'll assume here you believe they will be able to easily assemble a fully operational blowback operated pistol or similar device. This would require the ability to machine a barrel, cast a variety of plastic parts (the 'easy' bit) and assemble all the resulting mechanical bits into an operational weapon - one that is more dangerous in criminal hands than a combat knife, match head bomb or a crossbow.
That's a Glock 17 in parts
That's a GP-100 double action revolver.
Repeating pistols are complicated machines with many parts requiring specialty manufacturing. Yes it's possible to make a simple firearm with a 3D printer, but the upper limit is set by the assembly ability of the person in question and the access to workable materials- that in fact has been true for a long time with machine tools in no rare supply.
There are already plastics that are considerably stronger than steel, it's just a question of making them available as a printing medium. As the industrial demand for stronger plastics to make prototypes with grows, so will development into meeting those demands and, by proxy, stronger materials will become available for things like this.
Barrels are usually hammer forged and tempered in liquid salt to prevent catastrophic failure from faults along the grain structure. I don't think plastics match steel alloys in shock resistance, heat resistance, or fatigue resistance; unless they have now? I strongly doubt, but could be proven totally wrong, a plastic barrel would be accurate and otherwise reliable for very long, no matter the polymer in question.
It's the equivalent of a breadmaker - sure, anyone could have baked their own bread for years, but almost nobody did because it was a time consuming, a bit tricky and inconvenient. Replace that process with an automated one - insert ingredients and press a few buttons - and suddenly homemade fresh bread was a common thing. You didn't have to be in any way competent in the kitchen to make bread any more, and 3d printers - once they reach an appropriate level of sophistication and a low enough cost - will mean that you don't have to be in any way technical or handy to make relatively complex objects, including weapons. You wont even need the garage that NGTM1R is talking about, let alone the tools to fill it. That's a big deal.
But a crossbow or knife could easily be a superior weapon to the firearm that you printed out - and those you can typically just buy AFAIK. I don't know of a country that requires you to sign off on a Ka-bar, and in many situations it's a more dangerous weapon that even a real gun.
Thirdly, assuming the above prediction does come true - this will fundamentally change the way guns are regulated. Think about the recent failed attempts at gun control laws in the US - ideas about controlling things like high capacity magazines will go right out the window.
High capacity magazines already have startlingly bad reliability. Holmes jammed mid massacre, and thus many more people walked out of that theater. I doubt 3D printing will make a better magazine.
Eventually, the concept of attempting to control guns at all will be futile, unless they treat the downloading of a weapon schematic in the same way that they currently treat something like child porn - i.e. they have large, well funded and dedicated police forces looking for and prosecuting the people doing it.
No really, I think your argument just became "3D printing will become nearly limitless in the near future."
The regulation will have to shift towards things that can't be printed - things that involve complex chemistry - the bullets.
Bullets are, in many respects, the EASIEST things for an individual to make in the entire gun. There are whole communities dedicated to handloading. All it requires is lead, a mold, gunpowder, and primer. The primer and gunpowder can also be produced by someone with the right know how - and it's mostly not a complicated process - significantly simpler than making, say meth or crack.
I don't dispute that it will be possible to make weapons on a 3D printer off of plans from the internet. I dispute that they will be very effective. I dispute that someone holding up a bank with one will be any more of a threat than the same person holding up a bank with a musket, or a knife, or a bat.
