12.5" Melonite barrel

wilssoon · Apr 9, 2018

I'm a fairly new member here. I did some searching but couldn't find an answer. I just bought a 12.5 government profile 5.56mm barrel. It's QPQ treated, which I believe is the same as Melonite. The bore is significantly lighter in color than the barrel extension and outside of the barrel. Is that normal for a QPQ barrel? I assumed the treatment process turned the metal black. I only have experience with chrome lined barrels, so I don't have anything to compare it to. Thanks

jdindadell · Apr 10, 2018

Well, QPQ (quench polish quench) according to wikipedia is:

The process starts with a standard salt bath nitrocarburizing cycle, which produces a layer of ε iron nitride.

Next, the workpiece is mechanically polished; typical polishing processes include vibratory finishing, lapping, and centerless grinding.

Finally, the workpiece is re-immersed into the salt quench bath for 20 to 30 minutes, rinsed, and oil dipped. This last step optimizes the corrosion resistance by creating a layer of iron oxide about 3 to 4 micrometers thick. It also gives the workpiece a black finish.

So, perhaps they plugged the barrel after the polish step and did not allow the final Quench to get into the bore?

Or just the bore was polished a second time? QPQP?

Or maybe they only polished the bore, so the outside of the barrel will appear to be darker due to lack of polish?

12.5" Melonite barrel

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