22 lr bullets are responsible for more human deaths annually than any other caliber, so it will kill. Opinions of why this is the case are varied. Maybe it is just because there are more of these firearms and weapons than any other caliber in the country. Regardless of reason why, it is a known fact that they are responsible for many human and animal deaths each year.
A standard 22 round will penetrate a one half inch pine board at 440 yards which means at that distance, it still has enough energy to surpass the minimum requirement of around 50 ft lbs of energy necessary to create a mortal wound in a human. 440 yards is about the furthest even good shooters can hit a target. So the answer is, a 22 round CAN kill as far out as you can hit a target.
The warning on most 22 LR packages states that it can travel extreme distances. Once you shoot this little round at 100 or 200 yards you begin to understand that is an under statement.
Iraqveteran8888 conducted the test describe above. The rifle used was a Ruger 10/22 and standard 22 lr ammo was used. was fired at a one half inch thick pine board at varying distances starting at 100 yards. You can watch the test on the video below.
They do not deliver the energy of larger caliber bullets simply because of the velocity and smaller mass, simple physics.
In some of the human deaths I researched though, the little bullets were found to have ricocheted off of bones causing them to travel in 2 or different directions before coming to a stop. In many cases, this is the reason the shot resulted in death.
It's tendency to do this inside of a human is another property that makes this little round very lethal.
Another variable what is the target? We know it will kill a human as far as you can it a target, but what is the target. A deer, an elephant, etc. I am pretty sure it wouldn't kill an elephant quite as well as it would a deer.
In conclusion, the little 22 lr round is not a toy. It has the capability to take life at long distances. Don't play around with it.