Barrels: Nitrided Stainless vs. Chrome Lined 4150CMV

AR/M4 AR Technical Discussion
41

Ahh. I was under the impression headspace could be set with mix matched barrels and extensions. I see your point that would be stupid after treatment.

Is cleaning the threads more a corrosion issue or loosening issue?

For a stainless barrel…say your extension is torqued and port is already drilled. Before melonite, could you remove the index pin, take a flat end mill and drill further down into the barrel threads about .020" then press a longer index pin back in place?
Then when the barrel gets melonited, remove the pin and extension, clean the threads, and re-torque the extension until the pin hole lined up with the hole in the barrel threads? This way you solve the loosening problem with a pin stop and you’re able to clean the threads and re-torque to the right index.

Is there the chance it could then torque under spec because of the friction reducing properties of the melonite?

42

In my experience they will not line back up perfectly unless you torque to the point and disregard the torque value. If the extension wobbles on the barrel no matter how small, the accuracy will be terrible since that barrel extension is the only thing that connects the barrel to the receiver.
Years ago while on the road I had a 308 barrel made by a smith in the south west. The first 10 shots were great, near 1/2" at 100. then after that they just kept getting bigger. The barrel was loose in the extension. It could not be repaired without installing a new extension that was clocked early then the shoulder turned down to make the pin aline the gas port then the chamber recut to the proper headspace. I use an impact wrench to torque the extensions. Trying to hand tighten them in a vice, even a 80lb round part vice doesn’t work.

43

add in the way barrel is made HF vs. button …hammer is better way to go …the best way is NOT cheap !

44

In ARs, throat erosion will kill the bbl first. In which case nitrocarburizing is superior to chrome. I think at this point, chrome is little more than a vestige of an old manufacturing process. I can’t think of a firearms related application where chrome would be prefered over many newer metal treatments.

45

This obsession over barrels is freaking unbelievable.

Barrels are consumables. Shoot them till they die and slam another on.

46

Better? How? Less stresses in the barrel? Tighter dimensional control of bore dimensions?

What evidence do you have of this?

47

For all the amateur metallurgists and material scientists here: http://www.intechopen.com/books/heat-treatment-conventional-and-novel-applications/thermochemical-treatment-of-metals

48

REALLY good tchit, Alpha!

extra info: earlier in this excellent thread, ‘crystallization’ had been mentioned. ALL steel that is below the melting point ['bout 2600°F] is a crystalline solid. period. It may be ferretic [all carbon steel such as 1006, 4130, 4150, and the 400-series stainlesses, like 410 & 416]; it could be austenetic [304, 316, 321 stainless], it could be partially martensetic. But ALL non-molten steel is crystalline.

:cool:

49

Better? How? Less stresses in the barrel? Tighter dimensional control of bore dimensions?

Both. Evidence? Our military. Specifically, in the mid 70’s Rock Island Armory extensively tested M14, M16, and M2 barrels made with Steyr process CHF against traditional methods and found significantly improved barrel life, dimensional accuracy, and smoothness.

Several euro mfg’s and military users found the same, and still specify steyr process CHF.

Not really a surprise, the Germans invented CHF as a way to increase barrel life on the MG42. BTW, HHF and cold rotary swaging did not achieve the desired result, which was the more widespread mfg process prior.

50

CHF is THE way to produce a shitload of barrels QUICKLY. THAT is why the military loved it so much.

Yeah, they have had the shit cold worked out of them, which makes them pretty tough. It also makes them useless without a lot of stress relief (more $$). As far as your claims of surface quality and dimensional stability, they are entirely dependent on process control, just like they are in other methods of barrel making.

51

CHF was developed to churn out a large number of barrels quickly and economically, even with the added cost of stress relief. CHF isn’t the only barrel making process that uses stress relief.

Ask Grant about the difference between the life of Colt CHF vs button rifled AR barrels.

52

Where did you get this LW barrel?

53

I got it from Little Crow Gunworks through Gunbroker a couple of years ago. Great folks to work with

Their website
http://www.littlecrowgunworks.com/

54

Smoother bore, more consistently accurate chamber dimensions, longer lasting.

Evidence for this?

-Recent PiP projects regarding hammer-forged barrels.
-Personal experience with how much less fouling my CHF barrels accumulate than other methods.
-Fact that many CHF barrels have the chamber formed at the same time as the bore vs. cut separately. They are either all correct, or all wrong. Hopefully correct, lol. Also eliminated are burrs from the chamber reaming where it joins the rifling.

55

It seems like the issues are getting confused. The original question was over having a preassembled Noveske 416R barrel nitrided vs a hammer forged chrome lined barrel.

I’ve come to the conclusion that treating a pre-assembled barrel, regardless of whether it’s 416R or CMV is not ideal because the barrel and extension threads will contain remnants of the salts and will corrode. YMMV. Finding a 416R hand lapped and nitrided is almost impossible AFAIK. That would be the best of both worlds.

Don’t believe button rifled barrels can be some of the most accurate out there? Try Noveske, White Oak/Wilson, ARP, Shilen or Lilja blanks, and a handful of others.
Can you get a sub-MOA chrome lined barrel? It’s possible but out of how many? A few match button rifled hand lapped barrels even come with guaranteed sub-MOA accuracy.

Pick one and shoot it until the accuracy is sub-standard. Don’t over-think it.

56

Yep, that’s it. The military is willing to compromise MG barrel life to save a buck. :secret:

Care to cite your sources? I’ll cite mine:

“Cold Rotary Forging of Small Caliber Gun Barrels”
US Army, Rock Island Arsenal Directorate

Summary Comments:
[ul]
[li]Metallurgical analyses demonstrate that rotary forged barrels meet or exceed military requirements.
[/li][li]Improved grain structure, increased toughness, better corrosion resistance, and finer surface finish result from the process.
[/li][li]In general the geometry and surface finish of the mandrel are reflected precisely in the barrel bore.
[/li][li]Bore finishes of 8 micro inch (arithmetric average) or less are possible.
[/li]
[li]Rotary forged barrels exceed military accuracy requirements
[/li][li]Bore variation is drastically reduced and straightness increased.
[/li][li] Variations of less than .00015 inches are common.
[/li][/ul]

Benefits:
[ul]
[li]metallurgically improved weapons due to finer microsturcture.
[/li][li]much higher production rates for difficult to machine supper allow barrel materials required for rapid firing weapon systems
[/li][li]the ability to produce extremely accurate small arms independent of operator skills[/ul]
[/li]
The barrels they tested were .50 cal of various types, 7.62 GAU, M219, 7.62 MG’s, M-14’s, and M16A1’s.

Can CHF Steyr process reduce cost? Over a large number of barrels, yes. But requires a very high initial outlay for the GFM Machines and associated heat treat lines.

Can it make a higher quality product for less than what it would take to make equal product using traditional methods? For sure. But it’s not just a cheap way to make barrels.

Many people are lumping earlier hammer forged processes with the Steyr CHF, and they are not the same. US developed processes (Torrington) did not produce the same results. Hot rotary forging did not as well.

You are right about one thing… it is a process, and heat treat process is critical. Goof that up and you probably lose any advantage. But that’s a core production quality issue.

Is it surprising that FN and Euro mfg’d barrels with this process might be higher quality than Ruger/Remington??? Not to me.

If someone has data that FN or similar CHF barrels are not holding up as well as traditional rifling that would be very interesting data to see.

What I’ve read of the various M4 testing for the improved carbine and M4A1 was that the CHF barrels beat the traditional in every case. In fact, after one widely cited test, all M4 barrels had to be replaced, where none of the CHF HK416 or XM8 barrels had to.

I’ll be the first to admit that I’ve not done 50k round direct comparison tests on M4’ish barrels to publish a result that XYZ mfg CHF barrel will last X longer than traditional.

But I do know enough about the Steyr process results and history to state as fact, it’s not done just for cost savings!

But buy what you want. Most folks will not shoot enough to see the difference. I know what I prefer, and it’s based on the long history of CHF in premium arms. :dirol: