I started with the AR-15 platform and built several of them....6x45, 300 BO, 6.5 Grendel, 6.8 SPCII, 450 BM, 458 Socom......
I had a chance to fire one of my friends DPMS 308's and then decided to get rid of all but one of my AR-15's....a 300 BO in a pistol configuration that just handles too sweet in CQ to let go of it....and switch to the AR-10...the number 1 reason in a word:
FIRE POWER!
Well....two words! ::)
Why use a pop gun when you can have a real rifle!