5.56/.223rem

Flat top upper, or EOP.

Forward assist and dust cover.

18-20" barrel. Heavy or heavy fluted, .750" gas block 1:8" or 1:9".

Good trigger. I like a 2 stage, Giessel triggers are orgasmic, RRA's are fantastic, Bushmasters 2 stage match are great.

20-30rnd mags.

Or up the ante to a 6.8SPCII 1:11" 18". Recoil will be more so keeping the scope down on runners is a little more difficult, but they anchor dogs very nicely.

MagPul PRS isn't worth the money, but it does look great. Telescoping M4 stocks suck, period. Anyone who says they really like to use them in a hunting rifle is lying. I "don't mind" mine on my 16" rig, but would prefer something else, just haven't decided what yet.