Just reading a science fiction book in which the protagonist uses a diamond gun. It’s diamond so he can smuggle it past security checks. Would this be possible using today’s technology? And how much might it cost?
The bullets would trip any scanner or metal detector. FYI
Making a gun out of carbon fibre might be easier.
What about ceramics with ceramic bullets?
Diamond is hard, but it will shatter. This is the primary thing preventing the manufacture of ceramic guns right now. Very hard substances have found uses as coatings over gun parts, but not as primary materials.
Should have made it clear - with diamond bullets!
So the shattering makes it impossible? Or is this something that manfacturing techniques could perfect over time?
BTW: I’m not a terrorist. Honest.
EDIT: I realise that metal bullets deform so a diamond bullet would shatter if it hit a hard enough material. In the story the character is an assasin wanting to kill a murderer, though he uses it to blast his way out of a space elevator window.
That’s good, I was a little nervous there.
Well, you wouldn’t get it past an eager TSA groper anyway unless you designed a way to stow it in your hoohoo.
Ouch. This is the secondary reason I’m not a terrorist. The primary being, y’know, the whole non-murdering/non-zealous thing.
Yeah right, no more of terrorist than this fiendish guy that hid behind his exoctic weapons material. 
This is exactly the issue with your diamond gun. People tend to confuse hardness and toughness, but they are two separate things. Diamonds are pretty much at the top of the scale for hardness. If you scratch a diamond against pretty much any other material, the other material always gets scratched and the diamond doesn’t.
People misunderstand this, and you can find references all over the internet to the fact that you can’t break a diamond even if you hit it with a hammer. This is very much false. Diamonds are very hard, but they aren’t very tough. It is true that diamonds always win the scratch test, but if you hit a diamond with a hammer it will shatter. You can chip a diamond just by whacking it against a shopping cart, which is something that jewelers specifically warn buyers of diamond rings about.
Your science fiction author fell for this common mistake. A real diamond gun would shatter rather dramatically if you attempted to fire it.
A non-metal gun only fools a metal detector. Anything gun shaped, metal or not, will show up on those new full body scanners that everyone is complaining about.
ETA: Unless, of course, you can shove it somewhere where the scanners can’t see it (ouch).
The author is Alistair Reynolds who has a phd in astronomy and a masters degree in engineering physics - so it’s suprising if he’s made such an elementary mistake. His get-out is perhaps that the novel is set in the far future!
Where the properties of diamond are different from today?
I don’t even think you’d be able to get a diamond into a “gun shape”. I’m no gemologist, but IIRC gems can only be cut along cleavages, I think they’re called? Basically, you can’t just take a diamond, even if the raw starting piece is big enough, and form it into any old shape. It will have facets and only break along said cleavages. So good luck getting several inches of perfectly smooth, round diamond for the barrel, or bullet, or a piece precise enough for the firing pin.
Okay, now I’ve named him I’d better be fair to the author and spell out his description of the gun, beause I slightly misrepresented it - he’s included fulleren (Fullerene - Wikipedia) The original question still stands though it looks like that’s a no. But how about the author’s invented gun? i.e a gun made entirely from carbon?
“The gun was tiny and semi-translucent, a haze of tiny components visible beneath its smooth, lucite surfaces.
It was a clockwork gun. It was made completely out of carbon - diamond, mostly - but with some fullerens for lubrication and energy storage. There were no metals or explosives in it; no circuitry. Only intricate levers and ratchets, greased by fullerene spheres. It fired spin stabilised diamond flétchettes, drawing its power from the relaxation of fullerene springs coiled almost to breaking point. You wound it up with a key, like a clockwork mouse. There were no arming devices, stabilising systems or target acquisition aids.”
Even if the firing is a spring, rather than rapidly-expanding gases from a chemical reaction, there’s still going to be a violent impact if you’re getting a bullet from zero to 700 m/s over the course of a couple inches. I doubt diamond could be used for much in even a spring-loaded gun. But I don’t know why some kind of exotic carbon-fiber/buckytube composite couldn’t be used. I don’t know if current materials could store enough energy in springs to fit in a tiny handgun, but I’m OK with allowing some magic- I mean as-yet-unknown tech - spring material.
A tiny pistol is going to be less accurate; I don’t know that there’s any technology that can really overcome a short barrel (and the inherent difficulty in accurately aiming something relatively small compared to a human hand).
Given enough technology that space elevators are possible, I don’t see any reason an all-carbon gun wouldn’t work. I’m not sure it would be diamond and fullerenes, and I think the author dropped the ball a little there.
Still, you could do some hand-waving and say that those are reasonable substitute words for some futuristic carbon nanostructure we don’t have today. After all, the main difference between graphite and diamond is whether the carbon-carbon bonds are nice, neat planes or tangled messes. There’s a lot of room for variation between those extremes and future engineers might find some combination of bond ordering that preserves the appearance and strength of diamond, while mitigating enough of the brittleness to make the gun work.
Maybe it’s even a solution that mirrors the way concrete is reinforced with steel. Either component could not achieve separately what both can do together. Carbon fibers embedded in diamond could be a similar solution.
Never read the book in question, but at a guess the gun (or the parts) were ‘grown’ using some sort of nano-constructor that put it together atom by atom. In which case you could build just about any shape you want, if you had the constructor, some materials and some way to program and control it…including a diamond shaped gun.
Trouble is, as others have pointed out, it would shatter if you fired it. And if you had the nano-constructor technology (assuming that’s how they built the thing in the first place), there are plenty of other materials you COULD build a gun out of that would get through a metal detector. The trouble there being that a society with such technology wouldn’t be using metal detectors, and instead would probably have nano-bots that could crawl over a person and sniff out anything dangerous (or be able to do a rough scan of the mind for harmful intent or some other technology that would look like magic to us).
-XT
Perhaps an even better example: Scaramanga - Wikipedia
Won’t the burning gun power itself be a problem? Diamonds don’t survive an ordinary house fire, won’t a diamond gun scorch and eventually catch on fire like any weapon made out of carbon?