If your rifle will handle 5.56, the 55 grain FMJ bullets (M193) do not over penetrate at ranges under ~ 100 yards. At higher velocities the bullets will tumble when they encounter a medium with water-like density. The bullet breaks into fragments, creates devastating wounds, and frequently does not even exit. .223 is loaded to lower pressures, with lower velocities, and can over penetrate. At longer ranges the 5.56 does not tumble in flesh and can over penetrate.
Kyle demonstrated this quite clearly for us. None of his hits over penetrated, even when he hit that one guy in the right bicep. The bullet fragmented and destroyed the entire muscle. If it had gone straight through there would not have been nearly that much damage.
Do not use the lower velocity M855 round (63 grain). This round is both lower velocity and has a steel penetrator which will lead to the over penetration you want to avoid.
Food for thought! Thanks!
But, that said, I’d still like to go to as a primary moderate power rifle something with limited range and not loud (we are rural but not RURAL rural). And my wife would shoot it. The .223 is a bit much for her. The .22 lr is a bit too light for the job. I might look further at those .22 magnum or hornet options, but that HighPoint 9mm is inexpensive*, and ammo is cheap and available.
*$280 at Rural King, sometimes they have discounts / 10% off sales, and I seem to recall a concurrent rebate at times.