[red-beard]

Actually of that is hearsay.

The rounds do not "tumble" in air, or they would be horribly inaccurate. Almost all rifle rounds are heavier at the end and yaw once they impact.

.223/5.56 seems to fragment, possibly due to the high velocity.

.223/5.56 is a killing round. It may be "less" likely to kill than a 0.308/7.62 round.

There are "debates" on a rifle vs. a pistol at short ranges. One thing that was found, shotgun 0 and 00 buck penetrate walls better than 0.223/5.56. 00 doesn't spread out much in short distances. Each pellet is about equal to being hit my a .32 ACP, and there are ~15 pellets. Most pistol rounds do not fragment or lose much energy going through sheet rock.

A legal short (16") AR-15 with a laser sight adjusted to short distances is very easy to shoot, has very low recoil and requires a lot less training to be good than a pistol. This is why the M1-Carbine was developed - Better than a 0.45ACP, easier to train to be proficient, 20 round magazine for quick reloading, smaller/lighter than a battle rifle.