A .177 can easily kill a squirrel. However, if you want to kill a squirrel with one shot, you have to accurately aim at its sensitive areas like the brain or heart, Hence, it’s important that you practice and increase your accuracy if you want to kill as humanely as possible. Another option is to shoot from a closer distance. However, you may end up scaring away the squirrel. You can also use .177 pellet for other small game animals like raccoons, rabbits, and mice.