I decided to build an 18" rifle using a melonite barrel and nickel boron upper and BCG from WMD guns.
The barrel began as an 18" 416R stainless, standard profile, rifle length gas, 1/8 twist 3 polygonal rifling (3P) from Black Hole Weaponry:
Receiver, pre paint (gunkote):
WMD NiB-X BCG:
The barrel and gas tube were sent to Wynn at WMD Guns for salt bath nitriding (SBN) or melonite. Turn around took about 4 weeks. Everything came back a beautiful, uniform deep black finish. It took a bit of scrubbing to clean the bore post-treatment; you remove a brownish gunk to reveal a shiny black bore. The barrel originally had a bead-blasted finish so it came back matte.
I had a few extra tubes, so I sent them in as well.
Here is the final product. The rails are the 12" Rainier Evolution series. I love the light weight and slim profile of the Rainier rails.
The lower is from Kaiser Defense (wish I bought more of them when I could find them for $89/ea...), trigger is the Geiselle SSA. Magpul MOE+ grip.
Receiver plate sling loop is from arfcomer I Kick Hippes, the SLAP - I love the SLAP.
http://www.ikickhippies.com/
Buffer is Spikes ST-T2 with a Sprinco white "standard weight" spring.