In the hands of a skilled shooter, a .30 rifle is amazing.
There's a lot of variation in the ballistics and accuracy of .30 caliber rifles. A .30-06, .30-40 Krag, 30-30, and .308 Win all have varying capabilities of range, accuracy, and foot poundage. Any of those would be sufficient to kill a person, and all of the above calibers listed above have been used by soldiers in war, with the exception of the .30-30.
A 22 caliber rifle also has a wide variation, a .22 rimfire or .22 magnum is not the same thing as a .22-250 or .223, which are notoriously accurate calibers.