So for the past couple of weeks, I've been getting my yard ready for the growing season by popping squirrels off of my fence with a .177 caliber air gun. I usually use a bow when I do my yearly herd-management sweep, but my childhood setup was lost when I moved out of my parent's house this summer. That being said, I'm really not used to using an air gun for hunting, but most people get a lot of really good results out of them, so I thought I would give it a try. I've killed a few squirrels outright, but a few have gotten away mortally wounded. How does /out/ feel about this? Is it OK that I haven't outright killed all these animals? Is the suffering of a pest OK if it's not on purpose/occasional?

tl;dr I would love to kill some squirrels and get their meat/pelts, but it doesn't always work out so cleanly. Is it morally acceptable to fatally wound an animal and have it get away?