So, working on my latest, "because I can build" and looking for input. Here's what I have so far:

Aero Precision M4E1 upper and lower (really impressed with this pair)
LaRue MBT-2S trigger (love this thing!!)
Strike Industries enhanced LPK.
Magpul MAID grip
Magpul CRT stock (meh...)
BCM gunfighter mod 3 CH
Bravo Company Manufacturing A5 Intermediate Buffer System
BCM or Toolcraft BCG (about the same in my book and have one of each)

So, what am I missing, barrel of course which will determine caliber, muzzle device, handguard system (love Seekins, but would love to know some of your favs), and gas block/tube. Now here's where I get the mental block, what caliber???? 5.56 and 9mm are out, have both of those covered several times over. Was thinking in this order, 300 Ham'r (don't really hunt), 300 BLK (no plans on a suppressor, too many hoops) 6.8 (had one back in the day sold it, don't remember why).

What say you, great wealth of knowledge and opinion?? Is there a favorite of yours that I'm overlooking? Barrel, caliber, handguard????

Thanks for the input and before anyone asks, I have built many and build my own 1911's (a bit more tasking than an AR) and my budget for the missing pieces is about 500 or so.