I hunt a lot and a friend has a couple of airguns he hunts deer with. One is .38 caliber and one is .45 caliber if I remember right. They're quite effective within 100 yards or so. He charges them with a scuba tank and the charge will last several shots, they have the ability to adjust the charge pressure and thus the velocity with a valve.
I was quite amazzed at the full auto model, 30 cal with 16 capacity magazine.