I’ve searched on this issue and could not find much information as to what the average life span of a melonited barrel vs chrome lined on an AR.
The best and most recent thread I found basically indicated that it was too soon to know. See this thread: https://www.m4carbine.net/showthread.php?157676-Melonite&highlight=melonite
I didn’t want to resurrect an old thread so I am starting this one to see if there is any new information in this regard.
I would like to see some accurate data on this subject too.
Which one last longer is more of just FYI for me. I don’t think I could afford to wear either one out anytime soon. I like melonited barrels for their other attributes, the fact they wear slowly is just an added benefit for me.
Supposedly Melonite wears slower as its something added during manufacturing, bonding it to the metal. Plus it does not effect it’s accuracy.
Chrome is obviously mil-spec and, IMHO, would rather have it over a non-chrome lined phosphate, I would pick a CHF, Nitride or SS barrel over chromed.
PS - it’s really hard to wear out any barrel if not going full auto, or suppressed. Not impossible, but the LARGER majority of people never shoot that much through one gun.
Fact? I’ve actually read that they wear faster…
In my opinion, I think it has to do with how you shoot versus how long it will last. If you 10,000 rds in a weekend to shooting said number of rounds over 10 years (just a number I pulled out of my butt).
I don’t have the answer to your question, but I’m very interested to see any hard data on this subject. Thanks for asking the question.
Barrel life depends on a number of things, aside from rate of fire and how high the sustained barrel temperature is, the type of propellant you use has a lot to do with it. Double based powders tend to run hot and shorten barrel life. (I like to use cool, single base extruded powders.)
That said, all things being equal, (rate of fire, sustained temperature, flame temperature, pressure, etc.) a chrome-lined barrel will always outlast a nitride barrel. However, chrome is a heavy metal which is deposited onto the tube surface using aqueous electro-deposition. The chromic acid used in the deposition process is a hazardous substance because it contains hexavalent chrome. Hexavalent chromium is a major problem when it comes to environmental pollution prevention efforts and worker safety. Hexavalent chromium, in the aqueous liquid and misting forms, is a known carcinogen which is extremely expensive to dispose of because of its toxic nature. Chrome plating will only get more and more expensive.
For the above reason the Military has been constantly looking for processes that can replace chrome plated bores, especially in big guns. They haven found one that is better. All of the Power-Point and reports seem to show that nitriding only gets you to 80% 85% of the life of a chrome bore. For me, that plenty good enough given the price difference between nitride and chrome plating.
I’m having trouble finding the reports you speak of, is there one you can link?
I’d typically heard that it depends quite a bit on heat. At low temperatures, nitride should last significantly longer. At higher temperatures, they’re about the same. Of course, that was somebody on a forum and may be incorrect.
An advantage of nitride is that it doesn’t add significant thickness, unlike chrome, so you can make the barrel the exact size you want and then nitride it, vs chrome where you need to oversize the barrel/bore and then try to make the chrome the right thickness to get the right final dimensions. Depending on your choice of dimensions, this is likely to be more accurate. It’s the same reason serious match barrels aren’t chrome lined.
I would listen to what this guy says. My wife works in materials, corrosion prevention, and environmental compliance. From what I know from talking to her (I’m an aero, not chem), what he has posted about hexavalent chrome is exactly correct. That substance has been a thorn in her side for years.
I have heard similar, but I would also be interested in seeing the data.
I found some testing of Nitride vs unlined: http://www.superiorbarrels.com/Barrel%20Testing/Barrel%20Testing.htm but they don’t compare it to chrome. I know nothing about the source, found it linked from here: https://sites.google.com/site/freeballisticcalculator/black-nitride-melonite-and-qpq which I can’t verify either.
I’d really like to find it compared well to chrome lined but haven’t found that yet.
The answers you seek are usually in technology of machining and manufacturing textbooks.
Nitriding is usually an external treatment of the metal lending it surface-hardening, usually by gas treatment or salt bath immersion. Chrome-plating is an external plating treatment that adds thickness as chrome is externally added.
Nitriding means you have to start with a quality-rifled barrel of good alloy. A shit barrel nitrided will give you a surface-hardened shit barrel. A chrome-lined barrel may or may not last as long, depending on how it was plated.
Chrome lining starts to wear from the first round fired. Sectioned GI barrels will show you the throat goes first, followed by the chrome on the lands at the leade. Poorly-plated chrome barrels will wear faster if there are hydrogen embrittlement defects.
No barrel will last forever.
Your best bang-for-the-buck (so to speak, no pun intended) would be to start with a high quality hand-lapped barrel (preferably cut-rifled) and have it nitrided. If you plan to use it as a general-purpose mag dump blaster then any barrel will do – it will usually go to shit anyway as it’s exposed to high heat (the surface treatment won’t save the barrel as the base material is abused by excessive heat).
Superior Barrels in Georgia did an excellent job with Walther barrels but it didn’t seem to be able to keep up with demand. Pity, too, because they did some excellent documentation.
Excellent summary.
The ARL and other research laboratories have been developing novel innovative processes, but not just due environmental concerns, adherence to OSHA’s permissible exposure limits, and hazardous waste, as mentioned above, but also due to the development of modern and advanced propellants that have higher flame temperatures, coupling that with the propensity of cracks formed during plating process which provides a path of erosion to the substrate shortening life.
As lysander mentioned, research I’ve seen is primarily on large caliber weapons systems, I can’t remember the paper I read awhile back, that had some interesting test results, evaluating a case hardened tube, nitrided, and was hard chrome plated as well.
http://www.dtic.mil/ndia/2002gun/waterfield.pdf
While I was doing a literature review, stumbled on an interesting ARL article, noting the possible benefits of using high nitrogen based propellants that would reduce barrel erosion, by effectively providing in situ nitriding, though that would assume the bore was in the white.
Three of the largest gun manufacturers have tested CL VS Melonite and stuck with CL for the simple reason of longevity. If the Chrome is done right, you will get better groups over the long haul. Now if you say that you don’t shoot a lot and accuracy is what your about, then a good CMV barrel that has been properly honed will probably be a good fit for you.
C4
Sinister and Ming, thank you for your posts. Obviously if you start with a turd you end up with a polished turd, whether you chrome it or nitride it. I’m surprised how much faster the nitride Mk44 barrel wears out.
Can you tell us which manufacturers did the testing?
I doubt you’ll get an answer from that, as paid for knowledge isn’t normally public unless it can help sales. I would tend to agree with Grant on that what he has stated.
I know this is a thread about longevity, but I’d like to add something I experienced firsthand with a chromed and then nitride barrel.
I had a S&W M&P15R, the 5.45x39 version. It originally came with a chrome lined barrel. I shot Wolf 60gr through it without issues. Decided to make it into a pistol so I bought another lower (to keep it legal going to a pistol) and cut down the chrome lined barrel to 11". Again no problems. Later I decided to make a training carbine out of it and bought a Ballistic Advantage melonited 14.5" barrel and extended FH for it. Then I started having failures-to-extract. A lot of FTE. Never remedied the problem and sold the upper and ammo to a guy with the admonition to liberally use a chamber brush while firing or it would FTE.
Now, to be fair it could’ve been an out-of-spec chamber. Could’ve been the steel-cased Wolf (there is no brass-cased 5.45 that I know of). Or it could’ve been the Melonite. Not sure. I have an MR556 pistol that I had the barrel nitrided on. Granted, I’m using brass-cased NATO ammo but I’ve never had a FTE from it so far.
I’m sure this muddies the water a bit but from my limited experience steel-cased ammo + nitriding doesn’t do well.
They wear more slowly than non chrome lined, I have no idea of which one last longer, still just an FYI for me, as I will continue to use melonited barrels regardless of which one last longer.
Thanks for all the replies so far.