What is melonite barrel finish? Is it inside the barrel like a chrome lined barrel?

Yes.

How is it compared to a chrome lined barrel? Is it any good?

Yes, it's inside the barrel and outside. Without getting technical it's a treatment for metal that makes the surface harder than chrome and pretty slick

It's better than chrome

As noted in the reply above, from what I have read melonite is more durable than chrome.

http://www.thetruthaboutguns.com/2011/06/benjamin-t-shotzberger/%EF%BB%BF-gun-review-smith-and-wesson-mp15-sport/

CMMG's  WASP coating is pretty much the same thing. I had a couple of their AR's with this and had good luck with them, accuracy was good and the barrels cleaned up easily. I've also  heard it's better than chrome.

Melonite is great against corrosive munitions.

Stellite is good too.

Many heavy machine guns have stellite lined barrels.

I thought those were just the chambers?

The stellite barrels usually had a liner that went from the chamber out to something like 8 inches, then steel in front of that to the muzzle.  Only put it in the highest heat area of the barrel, but a difficult process to precisely machine both parts of metals and precisely fit them together to match up the rifling lands and such.  Really an amazing piece of technology.

Back to the OP's question, Melonite is a trade name for a salt-bath ferritic nitrocarburizing treatment process.  "QPQ Nitriding" is a generic term for that kind of a process.  Wikipedia has a reasonable page on ferritic nitrocarburizing, and if you want to see what the process looks like do a youtube search for "modern marvels salt" - the show "Modern Marvels" included some info on the salt-bath nitriding process in their program on "salt".  IIRC you skip forward about 30 minutes into the video to get to the nitriding part.

ETA:
Wikipedia:  http://en.wikipedia.org/wiki/Ferritic_nitrocarburizing
Youtube: http://www.youtube.com/watch?v=pCLzUcJrdOk  Skip to the 33:00 minute mark.

Unlike chrome lining, nitriding processes change the steel at and under the surface instead of adding a layer of material.  This allows more precise control of dimensions.  In addition, unlike a separate layer of a dissimilar metal, the nitrided layer is integral with the rest of the steel barrel and doesn't experience crazing from thermal cycling.  It's also much thicker than any additional layer like chrome, so a bore for example would be utterly worn and useless before you'd wear through the nitrided layer.  Nitride, when done to carbon steels, results in very corrosion resistant as well as very hard, durable surfaces.  Stainless steels are a poorer choice for salt bath nitriding processes because the different elements in the stainless alloys result in much reduced corrosion resistance, as well as lower heat resistance that's inherent in the underlying steel.  Nitrided stainless means more expense for a poorer performing product.

Which surface is harder? Nitride or Chrome?

Nitride is considerably harder than chrome lining

I dont mean to insult you, but are you sure? We are still using chrome lining in the military, is it institutional inertia? From what I understand meloniting is cheaper to do and makes consistent barrels?
Why are we still using chrome lining?

Inertia. It takes the military many years to make even the most basic of changes.

How would this (Melonite) work for bolts and BCGs? Or would it not be worth the cost?

J.P. Enterprises offers melonite carriers.

As an aside, Glock uses essentially the same process on their slides and barrels; as I recall, they have a different name for it (tenifer I think it is) instead of melonite.  There are variations of the "melonite" process –– different tempatures and maybe other parts of the process.  I think the Wikipedia article someone here referenced talks about the differences.  But, as others have said, the idea is to create a long-wearing and corrosion resistant finish that penetrates into, versus onto, the steel.

Ok started digging into it. Meloniting/Nitrocarburizing  gets ya  hardness ranges from 800 to 1500 HV depending on the steel grade.   Chrome hovers around 900 Hv and 1200 being the absolute maximum and  VERY hard to achive.
Thanks guys! this is VERY interesting.

Maybe I should give these barrels a try? LaRue melonites their barrels right?

No, LaRue uses LW-50 stainless.

That is the material of the barrel not the finishing process.

Still not melonited AFAIK, I believe that they "Ion Bond" the exterior of their barrels - Ion Bond is a trade name for a Physical Vapor Deposition coating process.  And as I mentioned, nitride in general is not the best option for stainless.... or rather, if you're going to nitride, stainless is not the best option.  From my understanding there are some lower temperature (non-ferritic) gas or plasma nitriding processes in development for stainless, but in general, why bother?  Nitrided CM/CMV steels offer higher performance at lower cost.


Because the specifications say chrome.

If you want to use melonite, get new weapons/products adopted that use it, along with a complete specifications technical package so that they know how to deal with it.

Despite the apparent advantages there may be some cases where chrome is still a better choice.  Something that used to get trotted out often was a couple decades old military test on 25mm cannon barrels where they compared a nitrided barrel (not sure what process) to the existing chrome lined, and got longer life out of the chrome.  Large caliber barrels for cannons and artillery do have some different characteristics than small arms barrels, or it may have just been differences in the process that was used versus current processes.

One thing that is often overlooked in the "newness" of nitride to the firearms market is that it's really not new, even to the firearms market.  HK for example has been using nitriding processes since the 60's, most all of their products have used some kind of nitriding (mostly gas nitriding) on various parts since that time.  Nitride has been widely used for parts for the oil industry and especially the nuclear industry for almost as long, as well as automotive and industrial parts and other users.  When I mentioned nitriding to my father he told me about his experiences with nitrided aircraft engine parts from the late 50's/early 60's.  It just hasn't been traditional for firearms in the US and not "mil spec".

Do you know how the friction coefficents compare?

Tenifer is correct.

Adams Arms uses Melonite on the bores and exterior of their barrels and BCGs of their 5.45x39 piston uppers. I have one and have only used surplus corrosive ammo in my rifle. It holds up extremely well. After almost 2000 rounds it still looks like the day I got it. I know thats not a lot of rounds but I've heard stories of untreated components exhibiting signs of corrosion if left unattended after only one shooting session. It appears to clean up and hold up extremely well.

I didn't know they coated barrel's too?

I don't care who ya are, now that was funny!

Gama762,

I have a LW50 Stainless barrel that was melonited, what should I expect from the barrle as far as preformance?  Does meloniting the barrel reduce the barrel life?  What about heat disipation?

762Gamma I got 3 of the Adams Arms 16" mid length SS melonited from spikes earlier this year  for $89 each. I wonder what I should expect? I had to open the gas ports to .067 for them to function.

I'm not a nitride process engineer just a somewhat educated consumer.

I'm curious though why many are so enamored with the idea of nitriding stainless when it's known to have issues, the base material is substantially more expensive, and its lower performance.

I agree.  I think the answer is that stainless is softer and easier to machine (cut the rifling) to a "match" grade status.  Most of the current nitriding processes for stainless may make it harder, but also reduce corrosion protection.  Until someone come up with an optimized process for stainless, it is better to have CV barrel nitrided......great hardness, corrosion protection, lubricity, without worrying about a dissimilar metal (chrome) being applied unevenly / light coating / heavy coating / flaking, etc.

Thank you sir!

I had always been under the impression that stainless was harder than CM steel, and its used for match barrels because it maintains a high level of accuracy longer.

Something like CM barrels gradually degrade and wear, whereas SS barrels are harder, and don't wear so much, but form micro cracks, and at 2000-5000 rounds (caliber dependant) parts of the lands chip away in the throat and there is a rapid decrease in accuracy.

My understanding is that stainless is quite soft, at least compared to CM.  Hard chrome is well......hard.  Stainless barrels will wear out faster than a non chrome-lined CM.  However, stainless tends to be more accurate.
The military uses hard chrome to make the barrels last longer under machine-gun fire and to improve corrosion protection, but that isn't news to anyone here.

I'm a little confused as to the nitriding of stainless barrels as well. I too have the above mentioned stainless Adams Arms barrel I got from Spikes, and IIRC AR Performance offered their 6.8 stainless barrels nitrided. (Hopefully they will come along and weigh in)
I started a similar thread in the precision section because I was thinking of having a 300 win mag nitrided for extra barrel life. After gamma brought it up, I did a little research and saw what he was talking about in terms of corrosion resistance. I was still thinking of having it done but painting the barrel afterwards for a best of both worlds kind of thing, but really, I'm not sure what to think.

Edit: I just remembered I also have a Superior Barrels "hard blue" barrel which I believe is stainless. I know thier process is a little different, but there apparently is a way to do it correctly...

I do not think the Superior Hard Blue barrels are stainless.  They were some of the first to do nitriding of AR barrels....at the first I knew about.

LedZeppelin is wrong in this case.

The typical stainless (416) is MUCH softer than CM/CMV steels, less resistant to heat, less resistant to wear, has less strength, and is more expensive.  Its values are corrosion resistance, and traditionally, the soft-as-butter nature of the metal made it easy to cut very smooth and precise barrels.  Unfortunately they don't last as long, and generally require heavy profiles, because of those same qualities.  There are some other stainless alloys which are somewhat harder and barrels made of some of those alternatives are available.

Hard chrome is for corrosion protection first and foremost.  Barrel life extension is a lot less than you'd probably think, especially in severe duty environments due to crazing and erosion of the underlying steel.  The cracking and erosion process LZ attributes to stainless is not far off from the typical wear pattern of a chrome lined CM/CMV barrel.


My understanding is that they are stainless.  IIRC they were working with a local nitride processing place and did a lot of experimentation to get the process adapted to stainless.  I don't know if they were using salt bath or some kind of gas or plasma nitride.

But, I'd ask again, why bother.  CM/CMV steels are less expensive, stronger, more resistant to heat, last longer, and more corrosion resistant after nitride.  In modern manufacturing with high hardness cutting tools there is less advantage to stainless as far as smoothness.

Pretty sure POF and LWRC were using nitrided barrels before Superior came into existance, Sig 556 was already on the market (but not an "AR").

I agree, which is why Harrison of AR15performance is cooling to the idea of nitriding stainless barrels.  The cost/benefit is just not there when compared with nitrided CM/CMV.

Interesting discussion here:

http://calguns.net/calgunforum/showthread.php?p=7681116