Does anyone have any firsthand experience with barrel nitriding?  Before I send off a barrel to MMI TruTec (in Arkansas), I'd like a little more confidence the accuracy of my .300 RUM (and later .270 Wby Mag and .338 RUM) won't deteriorate.  And, I'd like to double the barrel life of my Lilja 416R ss and LW-50 ss overbore barrels.  Here's the best of my research on this topic to date.  Can anyone add firsthand experience?  -- C. Smock

“Salt Bath Nitriding doesn't degrade accuracy one iota, unlike chrome lining. This was the first thing that I verified when I began using the process. I broke in a bunch of barrels and then machine rest tested them for group. I recorded and kept the targets, cleaned up the barrels, and sent them to MMi TruTec for the Isonite process. When they came back I reassembled them on the same receivers with the same torque settings, same bolt carrier assemblies, same flash suppressors, etc. Then they were retested with the same ammo lots. NO degradation in accuracy and about a 1% increase in muzzle velocity.”  -- butchlambert (the Armorer for the Army Reserve Shooting Team for over a decade), Sep 29, 2012

MMI TruTec calls their salt bath nitriding process “Isonite.”

“There have been many praises of this surface hardening treatment applied to rifle barrels in relation to extended barrel life, easier cleaning, nonexistent copper fouling.  However, there are some concerns that must be understood if you move forward with this. The temperature that the steel is brought up to during this process is within the range that can remove the temper from the steel if not properly finished potentially causing the steel to become dangerous and not contain the pressures your cartridge will produce. Any heat treating process done after the rifling process can lead to bore and groove dimensions and uniformity being changed. Also, the salt bath nitriding process produces a very hard surface finish. If the barrel IS NOT broken in prior to this process being done, it will never properly break in. If the barrel IS broken in there could be traces of copper left in the bore (even in the pores of the steel) and will react with the nitriding process in the form of pits or corrosion in the barrel where it reacted to the copper. The person or company you choose to do this operation must be aware of these items and would assume responsibility for what happens to your barrel as all of these operations and procedures are out of the control of Krieger Barrels, Inc. For the reasons stated above, the answer to this question is no.”  --  http://www.kriegerbarrels.com/FAQ-c1246-wp3352.htm

“BLACKNITRIDE™, or Ferritic Nitrocarburizing, is the thermochemical that simultaneously diffuses nitrogen and carbon into the surface of ferrous metals. During the process, a two-part surface layer is formed, an outer iron nitride layer with a nitrogen diffusion layer below it. During this treatment, nitrogen and carbon are absorbed by and diffused into the surface of the metal. Reproducible and uniform layers with a predetermined thickness will be formed on all areas of the metal.” – H&M Metal Processing

“The nitriding (or nitrocarburizing or Meloniting) is extremely uniform. At 62-65 Rockwell C it is a few points softer than hard-chrome at about 70 Rockwell C but since there is no surface coating there is no surface distortion.” --  Robert Forbus

“When it first comes back - I clean it with valve lapping compound. Recommended by MMI to get the process trash out.” – internet forum

The temperature required for the Melonite or carbonitriding process is much lower (about 1,100 F) than the critical temperature (about 1,725 F) of steel where the internal chemical changes take place. With the process [of Meloniting/nitriding,] carbon is moved up to the skin and added to the skin before a soft quench. It is basically a low-temperature casehardening with a low level (about 0.002" or so) penetration of hardened surface.  The temperature level used for Melonite is roughly the same as is used for the stress relief of the steel. Stress relief is an important step for any piece of steel regardless of alloy content if it is intended to be used for a precision application (such as a barrel) and cannot be allowed to change shape very much.  Until it is "killed" by artificial aging (precise heating and chilling processes) or by the span of many years (about twelve or so) a piece of steel is still "alive" and undergoing slow internal chemical changes that make it grow in size and change shape. The first annealing step does most of the "killing" and provides stress relief.  I will add this though - any imperfections (such as burrs) inside the barrel will be hardened as well and will remain there longer than they would have after normal use. Of course if one purchases a hand-lapped barrel these imperfections should not be there in the first place.

Best Regards,
Robert Forbus
Ing. Robert Forbus, International

I've seen great results & crappy results, it depends of who is doing the work.

One question for the experts out there,  can a barrel & receiver be done while assembled?

can you nitride/melonite/etc. a Remington 700 receiver without warping or damaging it?

I sure wish they would get this perfected.  I would gladly pay more for like a Krieger barrel broken in then nitride with double the life. Does anyone sell such a thing for savage maybe?

@ziarifleman

What?

Nitriding isn't going to make a barrel better or worse. It's just a surface treatment. It will make a good barrel last a lot longer. I don't know about bad barrels, I don't make bad barrels.

All the barrels I've had done shoot awesome. I wouldn't bother doing it on a factory tube.

I don't believe in break-in, so I can't speak to that, either.

One of the issues with the AR market is pretty much everyone is using, while not necessarily shit-tier, barrels of rather low quality. Nitriding won't fix that.

First off

Something no one seems to get right:

Nitriding DOES make it slicker...

BUT

Not as-slick as chrome.


It DOES VERY SLIGHTLY CHANGE THE MICROSCOPIC SHAPE OF THE SURFACE

If steel has already been heated treated (e.g. a bolt action receiver), my understanding is you don't want to nitride it, because that would be heat treating the steel twice, a no no.

can you nitride/melonite/qpq a stainless steel surface, like a barrel?

Yes, I had my Apex M&P 9mm stainless barrel melonite coated.

Don't believe in break in as in the clean shoot, clean shoot procedure? Or that barrels need some rounds through them before you are seeing its best accuracy?

There is a thread on M4Carbine about this subject. One of the guys from AAC advised that they have seen the sharp edges of the rifling become dulled/rounded after going through the salt bath process.