Cryptic Mystic Black BCG coating
 

I thought nickle boron was the premium BCG coating. Then I discovered Cryptic's coatings. Their top of the line coating is called "Mystic Black."
The entire Cryptic BCG in "Mystic Black" was a little too pricey, but just the bolt itself was just a little over 100 bucks. So what I decided to do was put a Mystic Black bolt on a relatively inexpensive nickle boron carrier.
Mystic Black is hard to describe. It makes nickle boron seem like sandpaper, LOL The Rockwell C hardness chart tops off at 80 HRC which is 1865 Vickers. Nickle Boron is slightly off the Rockwell C chart. Mystic Black is way way off the chart. Tungsten carbide is 2600 Vickers.

Mystic Black
Coefficient of Friction: 0.01
Hardness: 3000 Vickers
Max Temperature: 1,100° F
Thickness: 2-3 microns (0.00008" - 0.00012")
Color: High Luster Black

Nickle Boron
Coefficient of Friction: 0.5 – 0.8
Hardness: 1900 Vickers
Max Temperature: 600° F – 700° F
Thickness: 9–13 microns
Color: Silver – Matte Gray

do you have any pics Jim?

I'll take some tomorrow. Bedtime...

About to go take pics.
Meanwhile, I'll leave you with this...

Comparing DLC to Teflon:

Teflon coefficient of friction: 0.05-0.09
DLC coefficient of friction: 0.01
PVD (physical vapor deposition) coatings run around 0.5.
Multiple videos on YT show people cleaning up a DLC BCG with just a single wipe of a dry paper towel without using any solvent.

DLC has a higher max temperature - 1100°F compared to 750°F for Teflon. (some PVD coatings have around the same Max temp as Teflon, some higher)

Hardness...no comparison.
DLC 3000 Vickers.
Teflon 20-40 Vickers.

Carborundum has a hardness of 3100-3400 Vickers.

Here ya go. Old on top, New on bottom.
Now that I know a little more about BCGs, the old one was a real piece of crap. About the only part that wasn't was the bolt itself. Every other part had uneven wear or was chewed up. The gas key wasn't staked very well. Even the firing pin retainer and firing pin itself were all chewed up.

Perfect staking on the new Nickle Boron carrier.
On advise of an armorer, I will be lubricating the nickle boron carrier, but not the DLC bolt. The DLC coating looks and feels like it has oil on it. But it's dry as a bone.
https://i.imgur.com/J4Dk9kO.jpg

Very nice, I am not sure about that color but I am a function over beauty kind of guy.