Barrel Materials

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C7AR15

New member
I was flipping through a machining book and I came across a section on Thermal Conductivity of metals.
Copper and aluminum conduct heat the best.
Steel is in the middle.
and way down the list is stainless steel (also titanium)

Steel is 3X more conductive than stainless steel.

Have we been choosing the wrong material??
I know stainless is more durable in bad weather - but for target shooting regular steel seems to be the way to go.

A stainless barrel would hold the heat much longer and the heat from the chamber is not going to conduct through the barrel and dissipate.

What are your thoughts on this? what do bench rest shooters use ?
From the Wet Coast
 
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trigger643

New member
You'll find guns with high heat operation have carbon steel barrels. Stainless steel is marginally softer and therefore easier to machine -- and some argue -- easier to maintain.

A stainless steel barrel will shoot out faster than a carbon steel barrel due to its being softer. However, this is really insignificant. So you only get 9,500 rounds out of a stainless barrel instead of 10,100 rounds chambering .308? Darn. When a barrel goes, it goes quickly. Going from 2" to 4" groups may be acceptable to many. I generally rebarrel my target rifles when they'll no longer hold 1" at 100 yards. The champions generally rebarrel by measuring group deviations in millimeters -- tossing away what most of us would consider a perfectly good barrel with lots of life left.

Of course, if someone is more concerned with how much noise they can make in a short period of time vs precisely placing each shot (i.e. a rapid hot gunning), they will burn their barrel out much faster whether it be stainless or carbon steel, than if they took their time and paced their shooting, allowing the rifle adequate time to cool.

When I look at building a rifle, I look to see what the world class shooters are shooting. What stocks are they using? What triggers? Scopes? Ammo loads? What calibers? And what barrels ...

They are using Stainless Steel. (see: accurateshooter.com for more information).
 
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Bill DeShivs

New member
A lot of generalizations here. There are so many formulations of carbon and stainless steels that there is no answer. Stainless is not necessarily "softer" than carbon steel. Heat treatment also plays a very important part.
 
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trigger643

New member
Bill,

In the majority of CS barrels 4140 or a slightly modified formulation thereof is used. The majority of the barrel manufacturers use 416 stainless in their barrels.

4140 yield strength is typically in the 602,000 psi range, while 416 hardened and tempered is 586,000 psi.

416 also requires about 85% of the energy required in the machining process of 4140. This softness makes it highly desirable for barrel manufacturers as it's easier to work with.

While some barrel makers such as Lilja claim they get better life out of their SS than CS barrels in some specific applications, the vast majority find the opposite to be the case and even Lilja does not recommend SS for lathe turned solid bullets due to SS erosion characteristics shooting them.

See the full AISI descriptions of the properties of these and other steels at: azom.com. - - They go into great detail on the specific properties of steels in all conditions, with the results of specific types of hardness and erosion testing.
 
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Jimro

New member
4140 and 4150 are good steels for barrels. 4140 is also known as "ordnance steel" and 4150 is the milspec for M4 barrels...

Most match rifles I've seen in the hands of champions are using stainless barrels. Whether that is due to it being easier to make a high quality stainless barrel is a matter of debate.

The question of which barrel lasts longer is also up for debate. The chromium carbides in the stainless steel (and to some extent nickel content) will resist surface corrosion actions better than naked carbon steels. This is why you see tool steels for "hot work" usually contain a significant chromium content even if they are not a true stainless, such as D2.

Is that enough to offset the difference in tensile strength? Don't know, I'm not an engineer.

But I would recommend a quality stainless barrel if only because I see more of them winning matches.

Jimro
 
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chris in va

New member
If lead gets banned, we'll have to look at ceramic or some other material that will shoot the new metal. Copper will be too expensive...I'm thinking zinc.
 
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Sierra280

Moderator
I'm pretty set on having the next barrel I buy melanite/nitride treated. The evidence so far looks like it really improves barrel life. Plus, a bore that is as hard as chrome but doesn't change the tolerances (like chrome)!! What's not to like?!!
 
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Gunplummer

New member
Stainless can be hard to work with at times, but I guess the only cutting being done is the drilling of the bore. Cheap has a lot to do with all things. I have used a LOT of old barrels and they machine tough. The steel was a tougher blend than most barrel makers use now. The rifling was also cut and not burnished in. I had used some new barrels (15-20 years ago?) and when I cut the threads it was like cutting ledloy. The barrel maker actually advertised that their steel was "Re-sulpherized!". What that is , is dirty steel. The sulpher is added to help 4140 machine easier. Take an old barrel and drop it on a cement floor and it will "ring". Most new barrels have a "dead" sound. Cheap is everything now days.
 
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Jay24bal

New member
I'm pretty set on having the next barrel I buy melanite/nitride treated. The evidence so far looks like it really improves barrel life. Plus, a bore that is as hard as chrome but doesn't change the tolerances (like chrome)!! What's not to like?!!
Click to expand...

My sentiments exactly. I just ordered a new upper assembly for an AR this morning, and specifically picked one with melonite treatment instead of the standard chrome lining. After doing a lot of research on the matter, I saw enough to sway me into trying it.
 
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Jimro

New member
Gunplummer,

I think you are simplifying things a bit. The sound a barrel makes as it hits a concrete floor tells you nothing about whether it was accurate or not.

1, the hardness of a steel depends on the heat treatment in addition to alloy content. 4140 used in 1903 or M1 Garand barrels may have a few impurity differences than new manufacture 4140, but more than likely the new barrel has been stress relieved as part of the manufacturing process to ensure accuracy.

2, stress relieving a barrel, or any steel part, will take some of the "ring" and turn it into a "thunk" sound.

For those going with a nitriding process, make sure you get a standard steel barrel. Stainless steel does not do well with nitriding.

Jimro
 
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Jim Watson

New member
According to Hatcher, Garand barrels were speced for WD4150 Modified.
WWII 1903 barrels were WD1350 Special or Modified, with higher manganese than 4150 but no chromium or molybdenum.
4150 Modified and 1350 Special were resulphurized, 1350 Modified not.

P.O. Ackley quipped that WD specifications were so the Army had an excuse for not keeping up with SAE and ASTM standards.
 
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Gunplummer

New member
I have never used a Garand barrel for anything, but I believe there is a lot more nickel in 4150. Either way it is a higher grade than 4140. I like P.O. Ackley's writing, but if he was the endall to every question, he probably would have done the work himself instead of sending his projects out. I think I have run enough parts that were stress relieved to know what I am talking about. A lot of parts can be stress relieved in your oven. I never really had the cutting properties change just from stress relieving. Maybe you are over simplifying things and are talking about annealing. Why in the world would you start tossing around specs on M-1 barrels? How many people work down used or surplus M-1 barrels for a hunting rifle? If you want to use that, think about the old NRA Handbook for Reloading. The Frankford Arsenal tested military barrels and after tens of thousands of rounds continued to IMPROVE in accuracy. Why do your brand new better than ever barrels wear out instead of wear in? I am guessing cut grooves (More expensive, more skill).
 
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tobnpr

New member
Stainless Steel resists throat (heat) erosion better than chrome-moly, and will lap better.

It isn't about Rockwell hardness...
 
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Jimro

New member
Gunplummer,

The only difference between 4140 and 4150 is a nominal 0.1% carbon content. Nickel isn't found in the spec sheet for the 41XX series of steels.

Jim Watson,

You are correct, it is the CMP that uses 4140 barrels by Criterion, my bad for mistaking that with milspec.

Jimro
 
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Sierra280

Moderator
So what is the best barrel material for resisting throat erosion? Especially on overbore calibers?

--don't mean to hijack the thread, but it seems like whatever works well for something like a 7mmRUM should yield great life for a more conservative chambering.
 
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Jimro

New member
Sierra280,

Steel is an interesting material, you can make it hard which also makes it brittle, or you can make it soft which makes it tough. But you can't have both hard and tough.

You need hard to resist throat erosion, and you need tough to contain the massive pressures generated by smokeless powder.

If I were going to design a barrel for an overbore magnum, it would be a cold hammer forged chrome moly barrel in 4150 with a nitride coating. The hammer forging process produces a work hardened steel and the nitriding adds a surface hardening.

Still, with something like the 7mm RUM, I wouldn't expect too much in terms of lifespan. The real key to getting long life out of a barrel is to keep the pressures down, which is why the 7x57 Mauser has a longer barrel life (same bullet, lower pressure).

Jimro
 
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mete

New member
It's not "erosion" ! Erosion is the wearing away of the steel.
The problem is absorbtion of carbon into the steel .That in turn causes cracking of the steel in the throat.
Typical steels are 4140 and 416 for stainless. 416 is a free machining grade of 410 .It has higher sulphur content. A PPT hardening grade of stainless is also sometimes used.4150 is used too.
 
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ligonierbill

New member
Remember, 400 series stainless is ferritic. Usually when we think of "stainless", we are thinking of 300 series austenitic. Completely different alloy and crystal structure. Don't get too hung up on the barrel material.
 
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Sierra280

Moderator
It's definitely erosion. Shooting hot loads in calibers that are over bore capacity (like the 4000+fps loads in a 220 swift) you are, literally, blasting unburned powder down the throat and the barrel. Unburned/burning powder granules hitting metal at high speeds---picture a sand blaster!

Edit--that's why this is such a good thread, this is some really good info to have. When I rebarrel my swift (even though I don't load that hot) I would like to know that even if I do shoot some really hot varmint loads, I can still have barrel life beyond triple digits!
 
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