Thanks guys.
After checking out DPMS and other sites linked on MB site and listening to last week's podcast I now know why I've always stuck to pistols. Much less complicated. Load, point, blam! Smooth hole in target.
7.62/.308 lowers cannot be interchanged with 5.56/.223 uppers and vice versa. I did not know that. I knew 5.56 was not the same as .223, I did not know 7.62 NATO is not the same as .308 win. Apparently it is, and the DPMS site is messing me up by having two models chambered in 7.62 NATO mixed in with rifles they say are chambered in .308 win. Load, point, blam! Jagged, ragged 'sploded-gun shrapnel hole in Fatman! lol