It was an eyesore to the clone Gods from AR15.com so I finally compromised. I didn't want to spend $450 USD to get the right barrel, nor did I want to chop that precious original Colt HBAR (precious because it shot tight groups. Instead, I remembered that I had another 20" HBAR that shot quite well, and it wasn't a Colt. So then began the process.
First I gutted my Mk12 build and stripped the Colt 20" barrel off. I was left with parts all over the place. Next I gutted my M16A4 clone build, where I had used what was probably an 20" Olympic Arms HBAR
I planned to take the Olympic Arms HBAR to Reliable Gun and have it cut down and threaded into an 18" barrel, however reassembling my M16A4 clone proved to be a lot harder than I thought. First of all, I didn't have the original FSB that came with the HBAR, and I wasn't about to try and fit the one from the Olympic Arms one. Second, the rifle length gas tube from the Olympic Arms FBS refused to come out. I dug through my spare parts box and found an FSB from a 16" Colt LE6920 barrel, but I still needed a rifle length gas tube. Reassembly of my M16A4 clone would not be done this day.
Anyway, here are the two HBARs side by side. The Olympic Arms one is the barrel with the shiny bits where the FSB used to be. I'll have to remember to dig out the old Cold Blue and treat those bare spots.
The channels in the barrel for the retainer pins in the Colt HBAR were almost dead on to the holes in the Colt LE6920 FSB, and by the Hammer of Thor, I got those Goddamn pins in.
My Mk12 clone is now a real mutt-gun, with a Norinco A1 lower, Stag Arms keyhole forged upper and Olympic Arms chopped HBAR.
I got the barrel back from Reliable Gun and whoever they sent it do did a great job of cutting the barrel down to the clone correct 18".
The problem with the Olympic Arms barrel is it was not parkerized under the FSB. I took care of that with a spritz of Tamiya flat black.
On went the barrel nut and the hand guard retaining cap.
Torque on the barrel nut.
Making sure the holes lined up for the gas tube.
The pins that line up the hand guard,
The length already looks light years ahead of the 20" length.
With the crush washer, the break lined up perfectly with the tip of the barrel.
My Mk12 done.....for now. I may still try to source a Leupold Mark 4 2.5-8x36mm.
Another shot of the A1 profile lower.
The paint covering up the bare steel is still sort of noticeable.
With a few goodies added (just for photos).
Looks a lot better with the shorter barrel.