Jamaldog
Those cans or bottles filled with water are going to fool you a little bit.
This is because you cannot compress or squeeze water. When a can full of water is shot, it goes hydrostat which means that you get an impressive violent explosion.
It is kind of like a toy water pistol. When you pull the trigger, the water cannot be squeezed so it very quickly builds up pressure and goes a long way out of the end of the barrel.
I am thinking that you are testing your slingshot or airgun?
If so, you would be far better to fill the can with wet newspaper then see how it does.
Please remember that your slingshot or airgun has very little knock down power as compared to a rimfire rifle. They can give you the penetration that you need but it is very important to get good shot placement in the lungs or head for them to kill quickly.
