Since the gun debate has flared up once again, one of the most popular arguments I've heard is that a .223 (AR-15) bullet is no different than a .22 bullet you might use for plinking cans or rats. This is a very disingenuous thing to say, especially when it comes from a gun enthusiast who damn well knows the difference.
First of all, bullet size. A .22 Long Rifle round runs between 32-40 grains. A .223 is usually a 55-62 grain round, so the length and weight are significantly more.
Next, speed. A .22 bullet, depends on the load and grain, travels anywhere from 1,100 to 1,500 FPS (Feet Per Second). A .223 round leaves the barrel between anywhere from 3,000 to 3,600 FPS which is more than double the velocity of a .22 rimfire.
Distance? The maximum range a .22LR bullet is considered to be consistently effective at is 150 yards although I can tell you from personal experience that past 100 yards is difficult. A .223 is effective out to 500 yards.
I know a lot of people also like to say that the Sandy Hook shooter could have done just as much damage with a .22 but that's bogus. There's a reason SWAT teams and the military don't carry AR-15 rifles chambered with a .22. It's because it does not have the velocity and knockdown power that a .223 or 5.56mm does.
Long story short, if someone presents you with this argument, it's a load of crap, and they know it. It is basically a test to see if you know the difference when it comes to bullets, and if you don't, then they can then claim since you don't know the difference, you aren't qualified to talk about guns.