I have killed just about everything that walks, crawls, flies, or swims in the southern U.S. with a .22 long rifle, it would not be my first choice of SHTF weapons but I would not feel ineffective at all with my M-4 (with the conversion unit), GSG-5 carbine, or my Glenfield mod. 60 ( other than the reloading issue).
All of the usual suspects can say that a .22 is worthless for anything other than punching paper or sniping squirrels, but you tell that to all the "daisy pushers" that were on the receiving end of a .22, because more Americans have been killed by .22's than by .38's, .357's, 9mm's, and .45's combined.
As far as type of ammo, you can't beat off the shelf solid lead long rifle. Hollow points have thier place for improved accuracy, but I would rather have a more solid projectile for better penetration.
And on the effective range issue, best kept under 125 yards. I know that the BBB's (big bore bullies) are laughing thier heads off about now, and I know that it might not be a very effective single round stopper, but I know that I can put three rounds in a 4" circle at fifty yards before they recover from the recoil of their first round.
This is this! It's not something else, it's this
Don't pull it if you don't plan to use it, and don't use it if you don't plan to kill!
ALWAYS REMEMBER OUR MEN AND WOMEN OVER THERE