I'm considering breeding and freezing my own mice?

How exactly do you kill them? I don't think I could break their necks or anything, and just shoving them in the freezer seems way too cruel.
I know this sounds stupid, but I've never done with before.

The most humane way to kill a mouse is to make a Co2 chamber. they cost less then $50 to make all you need is a rubber made box, a paintball Co2 tank with a remote connecting them. If you go by youtube they have tons of videos on how to make them. Good luck!

I used to briefly work in a lab at a medical school, when I was an undergraduate. The most humane way is definitely a CO2 chamber (sounds kinda...genocidal, but you can do this to groups at a time). Years prior, they would break necks...but this was later deemed to be a less humane technique and was consequently banned. The CO2 technique is actually very quick.

CO2 is definitely the best way. Done right, they just go to sleep then die peacefully.

CO2 is the most humane way to euthanize them and have them safe for consumption. All you need is a plastic box, a CO2 canister from a paintball gun, and an adapter. Oh, and a way to make 2 holes in the box.

You are correct about putting them in the freezer as cruel. It is a long and painful death to be frozen.

Like everyone else has said, CO2 is the way to go. You don't have to have a fancy set up either (they can be very expensive). I use dry ice and water. I have a small cooler that I put the mice/rats in, and a container with dry ice inside with wire mesh on top so the rodents don't walk in it. Pour water on the ice, close the lid, and wait.

I use cervical dislocation when I kill my mice. The moment of panic they experience with C02 seems downright cruel to me. I have never had an issue with CD though. Always died instantly and since my mice are so used to being handled anyway, they had no idea what was coming. It's a matter of personal preference in some cases though and you absolutely NEED to know how to perform CD correctly in order for it to work.