[Unclenick]

You can buy tactical shotgun loads of #4 shot made by Federal that cut down on penetration. But other than frangible bullets, I am unaware of such things for 223. You could load light varmint bullets to mitigate penetration, I suppose.

M855 and SS109 would be something to avoid. Part of the impetus behind the development of M855A1 is to overcome the tendency of the older, standard versions to fail to tumble in soft tissue and instead to make a straight-through "pencil" hole that has poor stopping results. But M855A1, with its solid copper core and lack of start pressure reducing bands, is loaded to higher pressures and has been causing ejection system issues and short barrel life in testing, so I would not want to put much of it through one of my guns even if it were generally available. That said, since banded solids are longer than standard construction bullets of the same weight, they will fly with lower stability factors and be more prone to tumble if that's of interest to you, so you could look at ammunition loaded with them from the effectiveness standpoint. But penetration will tend to increase rather than decrease with them.