Just dont expect really good accuracy from dpms barrels. Their upper reciver is decent, ive got their a1 upper but i sourced the parts for it elsewhere. Dpms parts are metal injection molded and ive had forward assist break bolt hold open break and dust cover pin break.
If you go that route get the barrel and stripped upper and everything else from someone else.
1:9 will shoot 55 and 62 grain just fine but it may prefer one over the other accuracy wise.
"Gun control: The theory that a woman found dead in an alley, raped and strangled with her panty hose, is somehow morally superior to a woman explaining to police how her attacker got that fatal bullet wound." L. Neil Smith
The problem with being stupid is you cannot simply decide to stop doing dumb things...