An explanation of Nitride/Melonite/Tennifer etc

A couple posts ago, this one specifically, I wrote about different finishes for bolt carrier groups. I had come to the conclusion that a nickel teflon finish was the best of the current options for a bolt carrier group so that was my decision for what I would run in my AR-15.

I still consider nickel teflon to be superior to the more common nickel boron due to wear characteristics of the finish and there have been a number of other coatings which I have discovered in my research (I am especially intrigued by DLC or diamond like coating, more on that later,possibly). However, I have discovered that the information I presented in that post was incomplete, and nitriding really requires a post all its own.

First of all, nitriding is not new. Basically nitriding is a process of ferric nitrocarburization which infuses an iron base metal with a layer of nitrogen and pulls some of the carbon, inherent to the metal, to the surface. In it's basic form, this case hardens the metal and gives it increased wear & corrosion resistance. This is commonly referred to as Q, nitriding, Melonite (although sometimes Melonite refers to the QPQ version, more on that in a bit).

There are three main methods of doing this base level of nitriding: salt bath, gaseous & plasma. Not being a metallurgist, I am not really qualified to common on the pros & cons of each method, I assume the differences come down to trademarks & cost. I have not, through research, been able to discern a functional difference at the base level of this finish. However, the advantage of the salt bath process is that it leads to two additional finishing options: QP (Quench-Polish) & QPQ (Quench-Polish-Quench). It is important to understand that at the base level (Q only or use of the other two methods), although the hardness and corrosion resistance of the metal has been improved, the lubricity has not (if it has, it has been improved only marginally). More info is available at the wikipedia page here.

QPQ is the most common improvement of this process and is in my opinion the best an a very worthy competitor for other "premium" finishes. The QPQ process gives all the advantages of the regular process along with a much better coefficient of friction. It is not going to have as good a dry (unlubed) coefficient of friction as NiB or Nickel Teflon, but lubed it will be very competitive as we see in the chart to the right.

So, coming back to bolt carrier groups, how does this information help us and does it change my opinion?

Looking around, we actually see the cost of nitride bolt carrier groups to be equal to or less than that of regular phosphate. Most Mil-spec bcg's are chrome lined in the gas key & bolt channel & nitriding is a better solution in both of those areas for both lubricity & wear resistance. Also, the debate between carpenter-158 vs 9310 steel for the bolt is less important when the surface has been hardened to the 60-70 rockwell level. Basically, this process is an improvement on the mil-spec in every way (properly staked gas key is still really important as this process does nothing to help keep the key on the carrier).

The coefficient of friction is something that is very important and people seem to understand the least. The bolt carrier group is just like a piston in a car engine in that it moves back & forth in a channel under heat and with the introduction of soot and carbon into the system. Oil is a great solution to help lubricity but heat can cause it to evaporate & the soot and carbon can render it to turn into sludge and become counter-productive (this is particularly an issue running suppressed). The traditional solution of "run it wet & clean after x rounds" is completely fine, but less friction will always be better and allow the weapon to fire more rounds with easier cleaning in between. Going back to the car analogy, think of it like being able to go 10,000 miles between oil changes instead of 3,000.

In summary, is nitride better than phosphate? Yes, no contest. Is it better than any of the other coating options out there? It depends.

 I actually purchased a bolt carrier group from Apoc Armory to review(this one), and at $90 it should perform as well or better than any phosphate BCG (detailed review coming). In my opinion, if money were no object, I'd still prefer nickel teflon as I think you can get excellent performance dry from them, I'd also like to try out the diamond like coating. However, neither of those options come in close to the price of a nitride BCG and for the price, I think nitride is still very competitive.

Stay tuned for a detailed review, and I can be reached here with any questions, comments & for product reviews. . .