I read the responses so far and I thought I would try.
Those bullets you bought have lead cores, steel jackets, and a copper wash or thin coating on the outside to keep the wear to the barrel down somewhat. Since the rifle is not a precision rifle the wear and tear from the firing of the bullets will not be significant but there is wear or erosion from every shot.
Steel core ammo, like US issue green tip(M-193?) has a steel core or penetrator rod. A cheap copy of the original FN 5.56 that had a tungsten core.
Anyhow, neither the steel jacketed nor the steel core is appropriate for any indoor range (or outdoor for that matter) that uses steel backstops to redirect the spent or shot round. Neither should be shot at steel targets, armor plate or not, but the steel jacketed won't do as much damage. (it is designed to be cheap not good.) For outdoor ranges with earth berms and impact surfaces, either should be equally okay. Ranges that have sand or dirt covering sloping concrete (i.e. Gunsite's south range) my vote is no but the NRA Range manual says okay.
Hope I haven't confused the issue.
Steve