Original Colt M16a1 parts, I threw the idea of using all new parts around but just couldn't pass on owning the real deal and I wanted it to be historically accurate, I'm going to use a quality LPK and bcg to insure she runs right. Ordered a new manufacture 20" A1 profile 1/7 barrel from McKay http://store.mckay-ent.com/parts/m16-a1-replacement-barrel.html Yeah I know 1/7 isn't correct, but it'll make for a better rifle overall. I picked up the Colt upper, slip ring assembly, handguard retainer and FSB from Apex. https://www.apexgunparts.com/ They aren't the cheapest but their parts were in the best overall condition. It's going to be a long build, I still need to decide what lower to go with until I get a true A1 or Xm spec lower fom NoDak Spud. http://www.nodakspud.com/AR Lowers.htm Will be refinishing the rifle with Norrells moly resin and sending the upper parts to Adco for assembly and removal of the flash on the FSB. I'll throw up a build thread when I get a bit further in, wish me luck.