The AR Lower I built up has now been completed. For those of you who were wondering about the proper size Allen key for the Magpul trigger guard screw, its a 1/16" (the right tool made it fit real easily, a pity they don't put the size in their instructions, or just throw one of the keys in with the part - but Magpul did quickly reply to my inquiry).
So the humble lower has gone from This:
Finally to This:
I purchased a CORE-15 Upper in 300 Blackout and had it slightly customized with an AAC 51T flash hider and an upgraded bolt carrier. Core 15 was great to deal with and know their stuff, so I certainly recommend them as an option if you're looking for complete uppers.
I chose the 300 AAC Blackout caliber as it offers some interesting improvements over the 5.56 while maintaining the same magazine capacity. Having shot one in West Virginia it was fantastic - accurate, low recoil and a lot of fun, so I had to get one for myself.
I'm quite happy with how it all came together and this weekend I'm taking it to the range to try it out.