Upphew,
To enlighten you a bit about kangaroos allow me to help you out a bit. I've never hunted anything but I do know something of kangaroo having lived in Australia.
1. Kangaroos are basically the deer of Australia. They're fast, agile and can even be dangerous.
2. Kangaroos come in different sizes.
3. Australia is a dry continent and the animals there are designed for it. They are only meant to breed in the 'good times'. Since the increase in population and farming the kangaroos have access to water more easily so therefore they are able to breed more readily.
Having known a few hunters I would say trying to shoot a kangaroo with a .22 wouldn't be too wise unless you were able to get up close to it which means the kangaroo was used to people. Most are skittish.