Well, we were originally writing about the SKS, so let's limit ourselves for the moment to the 7.62x39mm round.
In its case, it presents a relatively heavy bullet that's travelling relatively slowly (all relative to the 55-grain .223), and it definitely will penetrate more than two layers of drywall. Thus it is inappropriate for use within an occupied dwelling.
Note, please, that at no time was I discussing the AR-series of rifles or their ammunition. That was someone else's addition.
Note to skullfr:
"Battle rifle" is no description of the SKS.
The ultimate "battle rifle" might've been the SMLE, if one were to judge from its conditions of use.
In order to qualify as an infantryman, the British soldier armed with the SMLE had to fire as many shots as possible in one minute, on the silhouette of a man's head and shoulders that was 300 yards away, and make at least 15 good hits.
It takes a real battle rifle, to do that.
(Try it, some time—even with a scoped semi-auto.)