Sorry, but you need to hear the other side of the story before pulling out the wallet. No way would I spend $850 on that DPMS. A little patience can give you a much better AR for the money. If you want an A2 FSB then why settle for an OR gas block? Get what you want. Use this time to learn the platform and select what you want not just anything off the rack. Read Agent Tikki's AR Primer and keep watching for deals on better rifles. Compare PSA, you'll get a lot more for the same money.
Loctite the trigger pins... Where did you get that? Trigger/hammer pins don't walk out unless something is wrong.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek