No amount of Internet fame would motivate me to intentionally break a glass next to my desk. Glass is pain to clean up, and when you miss a tiny shard, you will know it... someday.
The egg splattering on to the keyboard would not happen because there is not enough kinetic energy in that small bullet to make it splash back very far, the lightbulb though for sure put some fragments in to his keyboard because the shards bounce off each other and will cause some shards to go in the opposite direction of where the bullet came from.
What difference would barrel length make? Most BB gun barrels aren't rifled, and that's the only thing I can think of that would make a longer barrel more accurate.
Being rifled imparts spin to a bullet, being long compared to the length of the bullet gives you the ability to align the barrel with the target. The shorter the barrel the bigger the chance of mis-alignment.
Barrels were long before they got rifled. Rifling is mostly to keep a bullet on its trajectory once it leaves the barrel, it doesn't do much good if you can't aim the gun.
A longer barrel definitely makes it easier to do this though.
I wonder how the mass adoption of 3D printers will increase the availability of guns. I mean, you can just download and print one (if the material used when printing is strong enough, of course).
And it doesn't stop there. A friend of mine is a transhumanist philosopher at Oxford. He ranks home made viruses as the number one threat to mankind this century.
So far as I know, no plastic guns exist, our plastics technology just isn't there yet. Even if it were, it wouldn't be the same sort of plastic you feed into a 3D printer, or at least any off-the-shelf one.
I too have wondered about this. I also wonder about machinists moonlight as arms manufacturers :P
You could make everything on a gun out of plastic (commonly done), except for the parts subject to the detonation and bullet (chamber, barrel). Those COULD be made from ceramic. A plastic projectile would also be possible (it'd need to be pretty dense; not sure how best to do that -- it would still look like a bullet on an x-ray, unless inside something else, in which case you might as well do lead inside a form-fitting lead case, inside another object)
Not all 3d printers use plastic, there are processes for most metals including titanium. They work by depositing layers of metal dust and fusing it with lasers. The resulting parts can be very strong depending on the process.
The amount of extra material needed because of the structural weakness of sintered/deposited materials as opposed to machined materials would probably make such a gun fairly bulky, unless you are willing to take the risk of the breech portion exploding when firing the gun.
You could offset that to some extent by using less powder in the charges or you could use the gun for what they're used most for anyway (threat, rather than use).
Some companies are very far now in the production of single units or small series of parts for prototype or one-off purposes, every year the field moves ahead steadily and it is very impressive what can be done, but there is no substitute (yet) for a single properly treated chunk of steel machined to the right dimensions.
Parts made like this are rapidly replacing machined parts in places where strength is not such a big issue, you'll find them in just about anything that has a mechanical component to it. But they are not yet able to compete with machined materials for the most demanding applications.
Especially tensile strength is rather low, and pieces tend to be brittle.
Very few parts of guns require high-end machining and materials (barrels, specifically, are difficult/expensive). These are also not particularly highly controlled -- the barrel for a rifle can easily be repurposed as the barrel for a machine gun.
(A badly made barrel could be totally usable for a combat weapon; it just wouldn't last for 100 years and put a bullet into a palm sized group at 500m)
Receivers are historically the one part of a firearm which are considered to be "the firearm", and are not subject to particularly high stresses, especially on the AR-15 design. They can be machined by relatively incompetent people from aluminum, or made from plastic (Cav Arms sold these commercially for a while).
Guns just aren't that hard to make. The hardest parts of firearms to produce clandestinely are powder and primers, since that's more a chemistry problem than anything else. I'm not sure what the state of the art is in homemade smokeless powder, but black powder would be possible to make on your own (if a bit dangerous).
It is neither illegal nor immoral to own a gun. Strange thing to wonder about - where I hail from you might as well wonder about the availablility of toasters.
When I saw the title of this post my brain brought up mental images of 'minigun' and 'autocannon' and sort-of combined the two, and as such this really wasn't what I was expecting... neat, though.
Also, how does this compare to a BB gun?