The damage a load of buckshot does in a single shot is equal to shooting a suspect 12 times with a .223. The US Army still teaches soldiers how to use a shotgun in urban warfare training. If you ask any law enforcement officer what is the best home defense weapon, 99% will say a shotgun.
That's ludicrous. A single 00 buck pellet does not cause nearly the same amount of tissue destruction that a single shot from a .223 rifle does, unless the rifle shot happens to be a glancing hit and the pellet is a solid hit on a vital piece of body.
FIVETWOSEVEN sorry to add to the off topic. But yeah, a lighter weight projectile traveling at a high velocity can be plenty effective on people while giving all of the wondrous advantages of low recoil and flat trajectory.
In the intermediate cartridge class, a smaller caliber's primary advantage is that it allows for higher velocity and better trajectory while also allowing the use of longer for caliber projectiles, which fly better and fragment better, which in many instances will make them more effective than a larger caliber cartridge using stubbier bullets (don't fly as well and need to be more carefully designed to guarantee fragmentation, and they often aren't) at lower velocities (less non-bullet mass wounding potential, less force acting on the bullet and target to create wounding mechanisms like fragmentation and hydrostatic shock, less distance flown before hydrostatic shock ceases to be a factor in wounding), and they can be lighter, allowing the soldier to carry more rounds for less weight.