Barrels: Nitrided Stainless vs. Chrome Lined 4150CMV

AR/M4 AR Technical Discussion
21

Are you planning on running suppressed? Is that the reason for the Switchblock desire?

My standard weight DD chrome lined barrel is a 1 MOA barrel with the right ammo. I am currently testing a BCM chrome lined barrel in a build for my wife and junk UMC ammo went 1 3/8" for 10 rounds. That barrel has potential. Handloads should easily push it under 1MOA. I have a Nitride CMV barrel in 6.8 that shot a 10 round 1 3/8" group at 200 yards last month. None of these barrels cost me over $250.

I have my doubts that a chrome lined barrel will go 20K and hold anything near 1 MOA, and I have the same doubts that a nitrided barrel will go that far also.

10,000 rounds is a minimum of $4000 for shit accuracy ammo. A barrel change out is something I can do in under an hour. Once the barrels I mentioned above shit the bed, I’ll just throw another one on there. The barrel is so cheap compared to the ammo burned, that I don’t lose sleep over whether or not it will run past 10,000 rounds.

22

Decided to take a step back and compare the real world accuracy difference between these two barrels today and dug up this thread:

https://www.m4carbine.net/showthread.php?t=61263

16" Noveske Recon Barrel:

Testing was done at 100 yards from a bench rest. A Leupold VARI-X III set at 25X magnification was used for sighting. I obtained three 10-shot groups using one of my standard hand-loads for 77 grain Sierra MatchKings. Those three groups measured as follows:

0.81”
0.93”
1.01”

for an average 10-shot extreme spread of 0.92”.

These three groups were over-layed on each other using the RSI Shooting Lab software program to obtain a 30-shot composite group. The mean radius for this composite group measured 0.28”. Here’s a pic of the best 10-shot group of the 77 grain MatchKings.

16" Noveske N4 Light Recce Barrel:

I performed an accuracy evaluation of my Noveske 16” N4 Light Recce upper following my usual protocol. Testing was performed from a distance of 100 yards. Firing was conducted from a concrete bench with the free-float handguard resting in a Sinclair Bench Rest. The rear stock of the rifle rested in a Protektor bunny-ear bag. Wind conditions were monitored using a Wind Probe. A Leupold VARI-X III set at 25X magnification and adjusted to be parallax free at 100 yards was used for sighting.

Using hand-loaded, match grade ammunition I fired three, 10-shot groups in a row. The extreme spreads of those groups measured:

1.29”
1.18”
1.31”

for a 10-shot average extreme spread of 1.26”. I over-layed those three groups on each other using RSI Shooting Lab to form a 30-shot composite group. The mean radius for the composite group was 0.37”.

After firing the above three groups, I fired an additional five, 10-shot groups in a row using the same set-up for a total of eight, 10-shot groups. The average extreme spread for all eight groups was .24”. I over-layed all eight groups on each using RSI Shooting Lab to form an 80-shot composite group. The mean radius for that composite group was 0.39”.

I think 3 10 shot groups is a pretty valid sample size. Even if this is two specific barrels rather than a sampling of multiple barrels from each type, its still a pretty darn good baseline IMO. 1/2 MOA difference between the tightest group from the Recon and the largest from the Recce, and only 0.17MOA difference between the largest Recon group and the tightest Recce group. I would expect the groups to open up a little with store bought match grade ammo, and even more so with standard grade ammunition, but these barrels are still showing some good accuracy potential regardless, and not much of a difference between the two really. I could see the Recon giving 1-1.1MOA accuracy with off-the-shelf match ammo, and 1.3-1.4MOA from the Recce with the same. Or do you think that’s too optimistic? That’s not much difference really, even at 400 meters it would only be 0.88"-1.72" difference in group size if my theoretical math is correct. Considering your already looking at a 4.4" group at best, even opening it up to 6.12" isn’t much of an issue for torso sized targets, and correct me if I’m wrong, but you’re not going to be taking head shots at that range unless you’re dead nuts on your range and windage calculations, right?

It would still be nice to go with the more accurate barrel if the nitride treatment would make durability equal between the two, but it looks like that’s still an unknown at this point. Out of curiosity, has anyone actually shot a Noveske CHF barrel to the point that they’ve seen any degradation in accuracy? I’m not necessarily saying to the point of being “shot out” or unusable, but just to the point that it’s a 2MOA barrel now instead of a 1.5MOA barrel?

I also dug up some more info from archived threads where a few members suggested that nitrided steel/stainless steel should have a better resistance to abrasive erosion than hard chrome, and we know it has better corrosion resistance, so the only factor in throat erosion we’re missing data on is heat resistance/melting point… Ironically its probable the most important factor of the three.

23

Yes.

When you put it that way, it makes more sense. I was under the impression that the CHF chrome lined barrels were pretty much bullet proof (no pun intended). I guess that’s not the case? I have read that naked stainless barrels will start to lose accuracy around 4000-6000 according to the NRA High Power guys. Not that they are unusable at this point, they just won’t have the same level of accuracy they started with. But I’ve also read they can lose accuracy much faster under rapid fire conditions.

24

The point of chrome lining is to enable them to withstand the heat of a combat weapon. If you want a switchblock, and you want it pinned, you will be buying a Noveske stainless barrel.

I was under the impression that the CHF chrome lined barrels were pretty much bullet proof (no pun intended). I guess that’s not the case?
Nope. I don’t want to throw any barrel makers under the bus, but I’ve seen a $400 chrome lined barrel from a top tier manufacturer, used by a well known instructor, that had dropped it’s accuracy significantly at 10K rounds.

25

I actually plan on buying the whole upper. :wink:

I don’t suppose you have any info on how nitride treated stainless would withstand that same heat for comparison, do you? You mentioned you owned a nitrided CMV barrel, I would assume a nitrided stainless barrel would perform as well or better in that regard.

26

This might help:
http://www.burlingtoneng.com/wear_resistance.html

27

I have no clue. I did not seek out the barrel based on it’s nitride treatment. I bought the barrel based on the reputation of the builder as making a high quality, economically priced barrel. I don’t fire it rapidly because it’s a 6.8SPC and it’s mission in life is not CQB. I do not possess the proper tools to guage wear, measure temperature, or measure minuscule losses of accuracy as a barrel wears. I keep a log book. If or when the barrel no longer delivers the accuracy I want from it, I will replace it. Last, I don’t have enough money or time to wear out any of my barrels at this moment, even though I train weekly and attend classes. I spend more time dry firing and working on my fundamentals than I do shooting high volumes of ammo.

28

Dipping stainless…any stainless in 1400 degree molten salts will kill the natural corrosion property of stainless but the melonite treatment(the black or dark brown on a stainless barrel) then becomes the new corrosion resistance and the stainless is no longer stainless. I understand you want the stainless barrel because of the quality and switchblock. The barrel will be hard, the throat will not fire crack like it does on a normal stainless barrel or at least not near as quick.
I’ve made and sold hundreds if not thousands of Melonite treated stainless barrels. IMO they are more accurate than any chromelined barrel, even a cheap barrel melonited is more accurate than an expensive chromelined barrel. They wear very well so you get the best of both worlds. If you want to do mag dumps and blast get the chrome. If you want accuracy get the stainless. JMO

29

What if the barrel extension is already installed? How will that affect the corrosion resistance between the extension and barrel threads where the salt solution seeps in?

30

That’s the problem.

You do not want to nitride a barrel after the extension has been installed. Many, many stories about the extension loosening up from the barrel. The temps and process are so extreme, the two pieces loosen.

Not good.

31

From what I understand that wasn’t stainless barrels and it only affected a small batch. Some of the same barrels were not treated and had the extension loosen due to not being torqued to spec. So IIRC nitride treatment got a bad name due to a careless few individuals.

ETA:
You can also take a few steps pre-treatment to help assure the extension won’t loosen if that’s something you’re worried about. I’m asking about corrosion resistance of the threads and if the process will continue to react under there since the threads can’t be reached. The extension shouldn’t be removed after treatment. So I wonder if there’s an extra step taken that stops the reaction that wouldn’t be possible under the threads unless a chemical could be applied that would seep in between the threads and stop the reaction.

32

I believe that Constructor has written that his barrels are nitrided without the extension on, and have the extension torqued to spec and the gas port drilled in the proper location after barrel nitriding. This avoids the issue of salt issues in the threads, while it also means the gas port interior isn’t nitrided, which would be preferable (but may not really matter). I assume this would NOT work with anything that already had the gas port drilled, since the barrel extension at proper torque would probably not line up at the same spot that it did the first time it was installed.

33

Daniel Defense qpq’s the barrel assembly, and then re torques the barrel extensions, I presume they remove, clean threads, torque.

34

Hmm…I didn’t know Daniel Defense did the treatment in that order. Seems a little backward for them. It is possible to re-torque the barrel extension back to the proper alignment with the gas port but after being treated I was under the impression it would be hard to get the correct torque spec. Maybe I’m wrong.

From what I understand, getting the port to line back up after removing the extension is a pain even without QPQ.

35

“Nitrited barrels have the barrel extensions retorqued post finishing. If this wasn’t done, then yes, there would be problems.”-Daniel Defense, correspondence with me.

36

So evidently they drill the gas port after treatment as well.
Not sure why they wouldn’t just treat the barrels and extensions separately like some do IIRC. It seems like it would be more beneficial for the barrel and extension threads to get the full treatment.

I’m curious if they believe it to be a corrosion issue or potential for the extension to loosen.

37

I did not inquire further. DD knows what they are doing, and I left the details to the devil.

38

Not that I would rely on this but the two main companies that do salt bath nitride assure me there haven’t been any issues with treating assembled barrels.

39

I used the Nitrider (no, not David Hasslehoff) here in Phoenix who does POF’s Rock Creek Barrels. They are all done with the extensions on. He said he had never heard of POF having any problems but maybe for the few that do come loose, POF just isn’t notifying him.

http://www.cttaz.com/

40

How do you go back through several hundred extensions and match them to the barrel they came off of? There is a stamp, caliber and twist on the top of the barrel not to mention headspace where the extension is matched to a single barrel. I do hundreds of these barrels every month…unless like now every company is backed up 5-6 months. We have always treated both, removed the extension, cleaned the threads, retorqued, drill gas port.
Stainless extensions and stainless barrels treated together do not come as loose but I’m not going to take a chance and not remove and clean the threads.