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. . .

Why I chose to go with a nickel teflon BCG

When I was deciding what parts to go with in my AR-15 build, one of the first areas where I had a real choice was with the bolt carrier group. Sure, there are a lot of companies which make upper and lower combinations and you can choose forged or billet, but most of them will be relatively similar (as a side note, I am very pleased with the Aero Precision combo I picked out, more on that in a later post).

With bolt carrier groups there is a lot of variation in materials & coatings. I want to try to explain (based on my research) the various options and why I picked the one that I did (mild spoiler, I haven't actually picked one yet).

First of all there are a lot of different metals out of which the bcg can be made. I am not a metallurgist nor an engineer, so I can't really explain why one is better than the other. What I do understand is that there are certain areas that are prone to failure in the bcg and what a difference the coating makes in certain areas.

First of all, my understanding of bolt carrier groups is that the majority of failures involve lugs being sheared off in the extractor or issues with the staking of the gas key. This takes into account actual equipment error and not manufacturing error or issues in building the weapon. Most weapons, even in highly corrosive environments, shooting corrosive ammunition will not experience an issue on the actual bolt carrier itself. Additionally, although carrier tilt may have been an issue with early conversions from direct impingement to piston, it is less of an issue now and in regular DI rifles can be mostly ignored. Basically, any bcg that is milspec or better will perform adequately for even the most hardcore of AR-15 user.

So, if that is the case, why are there so many different types of bcg's out there and what purpose do they serve? All of the benefits of "enhanced" bolt carrier groups can be summarized in three points: ease of maintenance, frequency of maintenance & cosmetic appeal. Enhanced bolt carrier groups can run with less lubrication (some claim none and this has been tested. My upper and lower are cerakoted so theoretically I could attempt this but I'm not going to), are easier to clean (more on this later), and some of the various options look way cooler than a standard phosphate mil-spec bcg.

Nickel boron vs Nickel teflon/NP3 vs Nitride vs Microslick vs Phosphate

Again, not an engineer or metallurgist but this is my attempt to breakdown the advantages & disadvantages of the 5 categories of coatings most commonly available:

Phosphate
Advantages: Cheap, easily replaceable
Disadvantages: Hardest to clean, requires most lubrication
A lot of people will say "just buy a mil-spec phosphate bcg and be done with it." To a degree, they are right. A good mil-spec phosphate bcg can run $65 or less and the weapon will function. However, the phosphate finish attracts carbon, can be the hardest to clean and has no inherent lubricity which means that it will need oiled to run at peak efficiency.

Nitride/Melonite/Tennifer
Advantages: Very durable, some lubricity, can be cheap, matte finish
Disadvantages: Not as much lubricity, potential for metal wear, not as easy to clean
Nitride is a newer option for bolt carrier groups. It has been applied to pistol slides for a while and barrels are using it to replace chrome plating. Since it is a surface treatment, it ends up more evenly and is very durable. It has the second highest rockwell hardness of the options (generally around rockwell hardness of 64). This could lead to issues as the bcg is harder than the upper receiver but doesn't have the lubricity of some of the other options which could cause wear. If I were looking for this type of bcg, it would be hard pressed to beat this one from AIM Surplus for value ($100).

Micro Slick
Advantages: Very high lubricity, very high temperature resistance
Disadvantages: Not a good option for gas key, generally aftermarket, not as durable
Micro slick is a form of cerakote that can be applied after the fact to the bolt carrier group. The best version of this (the one they say is used in nascar) is sprayed on and then heat cured, there is also an air cure version. This coating will have the highest lubricity and will be very easy to clean. It is relatively inexpensive as multiple places only can apply it. However, cerakote can be scratched off relatively easy and the coating is unlikely to last the life of the bcg. Also, it is hard to apply films like this in the gas key which is one of the areas which needs the highest level of corrosion resistance. At $30-$50 it is not a bad option if you already have a phosphate bcg and want to enhance its performance but I personally would not choose it over one of the other coating options.


Nickel Boron
Advantages: Highest rockwell hardness, excellent corrosion resistance
Disadvantages: can stain, may lose lubricity over time
Nickel boron is a very good coating for a bolt carrier group. Like Nitride it is very hard but unlike nitride it also has a very high lubricity which means its less likely to cause wear. It will operate with very little lube and mostly wipes clean. However, it can stain due to being very light colored & having spots in the finish that carbon can fill in (see pic). Another side effect of the finish is that the raised areas can wear down over time which will cause it to lose its lubricity and make it effectively chrome. Still, even at that point it would be no worse than nitride. Another possible downside for people who don't like "blinged out" weapons is that it is generally a relatively shiny finish. From a cost standpoint, it has come down a lot from the $200 range, quality nickel boron bcgs can be had for much less.

Nickel Teflon/NP3/Obsidian
Advantages: Great combo of lubricity, durability & cleaning
Disadvantages: Cost, not as many options
Finally, we come to nickel teflon/NP3/Obsidian. These are all a nickel base coating infused with teflon for lubricity. This coating will have a high initial lubricity like nickel boron, but retain it over time. It usually comes in a greyish tone although TR Enabling has an obsidian finish that is darker and very attractive. In my opinion it is not as attractive as the AIM  Surplus bcg I mentioned above, but from a performance and cleaning standpoint, nickel teflon based coatings blow away nitride. Sharps and TR Enabling offer bcgs in the $200 range with this coating.

So which one should you get? That depends on what kind of AR you are trying to build and what you will use it for. In a budget build, you would probably be fine with a nitride or phosphate bcg. I am building my AR for 3 gun and I am willing to pay a little more to spend less time cleaning so I am going to go with one of the nickel teflon options. I was initially going to go with the Sharps, but I read about some people having reliability issues with them (un-relia-bolt?) so I was thinking about potentially the option from TR Enabling. However, Right to Bear offered to let me try out their nickel teflon bcg once it is back in stock, so I'm going to take that option.

Any questions, comment below and I will try to answer them as best I can.