[John Chapman (OP)]

What would happen to a bullet made of ice? Would the shock/compression wave turn it back into liquid water before it hit its target? Come to that, what would happen if you were shot with water? It might be possible to fill a shotgun cartridge with water.
 

[Ethos]

What would happen to a bullet made of ice? Would the shock/compression wave turn it back into liquid water before it hit its target? Come to that, what would happen if you were shot with water? It might be possible to fill a shotgun cartridge with water.
 

I'm just guessing but; If one were to fill a shotgun with water, I would not be surprised if it blew up in their hands upon firing.

[John Chapman (OP)]

Why? If only the cartridge was filled with water (and the charge kept dry) surely the contents of the the cartridge would be propelled. Wouldn't it be a bit like firing those party poppers that are filled with glitter or confetti?

[Chemistry4me]

Close range with ice might work. I do remember water balloons hurt if you get hit by one, but the in a gun, the water might need to be 'packaged' with something so it does not explode until it hits the target.   

[Im a Geek on the Edge]

Water is intrinsically soft. A bullet is a solid object and the front of it is pushed in by the inertia of the mass of the rest of the bullet travelling behind. So the sharp tip is propelled into the body by the bullet’s total weight. Because water is soft and has no solid structure each molecule moves independently dissipating its momentum.

[Chemistry4me]

Well, if you're trying to kill somebody, that's a different ball game altogether.

[paul.fr]

http://mythbustersresults.com/episode1

[John Chapman (OP)]

Thanks guys

Well, there you go. According to Myth Busters:

The bullet was simply too brittle to be used.

They retested using slow-frozen bullets that were stronger than the ones they used previously. The bullets simply vaporized when the trigger was pulled.
 

Someone on the Myth Busters forum suggested that when trying to use frozen bullets, it’s probably better not to use gunpowder for the propellant, because of the heat and shock. Something like high pressure Co2 might work better since it would actually reduce in temperature when it expands. Either that or you’ll need to use some sort of holder for the bullet to control it's acceleration and reduce heating.

Geek's answer sounds like common sense, although water would still have the same overall inertia. I take your point that it would probably splay out spreading the force over a larger area and reducing the likelyhood of the bullet puncturing it's victim. That being said I'm sure I've come across a thin but powerful jet of water being used to cut through metal for engineering purposes.

Oh well. I'll have to think of another undetectable murder weapon. The mother-in-law is safe for the moment.

[RD]

... I'll have to think of another undetectable murder weapon.

Compressed air ? ... http://matcmadison.edu/facilities/ehs/pdf/Compressed%20Air.pdf

[Chemistry4me]

Yes, I was thinking that too. He stole the words right outta my mouth! []

[John Chapman (OP)]

Wow. This is from RDs link:

Compressed Air Kills:
In the U.K., workers were cleaning their clothing with compressed air. One worker stuck the hose between a fellow worker’s legs, from behind. The man suffered bruising and bleeding in the rectum; shock; air in the tissues around his stomach, chest and neck; his hernia canals in the groin area filled with air; the abdomen filled with air; his lower bowel was torn open in 3 places; the abdominal cavity filled with bowel material and blood from his lower bowel; and the lining of his abdominal cavity was torn in several places. Despite surgery, he died 3 days later.

It may not be undetectable but it's certainly a more entertaining way to see off the old battleaxe!
 

[lyner]

Just like the old detective story in which a guy was stabbed with an icicle in a Turkish bath.(kept in a vacuum flask) the weapon melted but they got the guy because of a tea leaf that had been the flask and ended up in the victim's chest.