Working on my world, I'm reminded of ice mages that can instantly freeze opponent using Ice Ray.

That got me thinking if this is possible in real world. The most promising method of instant freezing is using ice pack, which immediately absorbs heat when the chemicals mixed.

However, I'm skeptic of the freezing part. The best I guess such mixture can do is sort of frostbite in an area around the wound. That is fine to me.

What I'm asking is whether utilizing instant cold pack as weapon to achieve that effect is possible or not?

If yes, what form such weapon can be effectively used? Right now I'm thinking about gun and bow, but I'm open to possibilities.