What is so special about 17-4?

[Nitrox]

Can someone explain why someone would want to spend a disproportionate amount of money on a barrel made from this material?

[Hoplophile]

Longevity. If a 17-4 barrel cost 3x a normal 416R barrel but has 4 or 5 times the service life then it is a cost effective option for people who shoot enough that burning out a barrel or three every year is a problem.

[TigerStripe]

What do they cost?


TS

[Hoplophile]

What do they cost?


TS
Noveske doesn't sell the barrels alone, only as part of a complete upper. But the difference in price between an upper with the 17-4 barrel is about $600 so I can guess that they are about $1k depending on length, profile, etc.

[JLM]

TS, check his site for complete setup prices. I believe they are on there.

[TigerStripe]

Cool, thanks guys!

TS

[JLM]

Longevity. If a 17-4 barrel cost 3x a normal 416R barrel but has 4 or 5 times the service life then it is a cost effective option for people who shoot enough that burning out a barrel or three every year is a problem.

I'm not so sure I buy the 'longevity' claims made for this material. I've been led to believe that ANY precipiation hardened steel is subject to weakening when exposed to temperatures above the temper point. A quick search revealed the following:

http://www.azom.com/details.asp?ArticleID=1175


Both martensitic and precipitation hardening families of stainless steels have high strengths achieved by thermal treatments; exposure of these grades at temperatures exceeding their heat treatment temperatures will result in permanent softening, so again these grades are seldom used at elevated temperatures.

I guess it would depend upon your particular application, but on the surface it would seem these types of materials would not be something you would want to use for sustained fire, where you could possibly exceed the temper point of the material. To me it looks like you have to keep it cool to avoid permanent softening of the material.

If anyone else has any more relevant technical data, feel free to chime in. This is an interesting subject.

[Hoplophile]

I'm not so sure I buy the 'longevity' claims made for this material. I've been led to believe that ANY precipiation hardened steel is subject to weakening when exposed to temperatures above the temper point. A quick search revealed the following:
Agreed. But so long as you keep it under the temper point it should have a longer service life than other steels. The temper point used on NRW's barrels is fairly high, as I recall.

[bigbore]

Agreed. But so long as you keep it under the temper point it should have a longer service life than other steels. The temper point used on NRW's barrels is fairly high, as I recall.


17-4 hardening temps start at 900(f), the higher the hardening temp, the softer the temper -- most barrels in the past were made to condition H1025, the last number of the condition is the tempering temperature... so condition H1050 17-4 was tempered at 1025.

Steel manufacturers do not recommend using 17-4 in applications that will subject it to exposure and soaking in the temperature range of about 700 to 900 degrees (f) -- but it is arguable if a rifle barrel "soaks" in that range long enough to be a real concern, some situations certainly could.

Steel manufacturers warn against using it in applications that will subject the steel to temperature within 50 degrees of the temper point, therefore a rifle barrel would have to be kept below 975(f) under all conditions, and that’s not gonna happen with a autoloader.


From what I’ve found it makes a great prop drive for ocean going vessels, because of its strength and corrosion resistance.

Grade 630 (or 17-4PH) is an "age hardening" steel -- its low tempering temperatures are great for stability and it can be made pretty hard. It has been used in the past by several different companies for barrels, but most drop it. I’ve talked barrel makers, steel manufacturers, and none recommended 17-4 for a rifle barrel. I wish someone could explain the benefits related to cost of 17-4 barrel over a chrome lined 4150 barrel? I keep hearing the “accuracy” argument, but a good chrome lined barrel is more than accurate enough for a “fighting” gun – meaning capable of 1 MOA with good ammo.



I want to buy 2 17-4 barrels
One chambered in 6.5x284 for a T2K. I will give it to a friend who is a long range high master. A Krieger chambered in 6.5x284 will last about 1000 rounds. If 17-4 is as good as advertised, it will be obvious in this application.
This is something that can be tracked and documented.

I want another barrel to take to Knob Creek. I want to put in an upper to pass around. Lets see how it looks after a weekend with thousands of rounds through it. With no fouling, it should be fine.

[SuicideHz]

17-4 barrels would be nice if you burn through three per year but not when you have to buy a complete upper or weapon with it. At that point, you might as well buy 5 barrels at a time from WOA or someone similar.

I believe K.L. Davis tried making this point not too long ago and then it came up again recently on TOS.

[JLM]

I wish someone could explain the benefits related to cost of 17-4 barrel over a chrome lined 4150 barrel? I keep hearing the “accuracy” argument

I never quite got that either, especially in short platforms with their reduced fragmentation ranges. 1 MOA would be perfectly fine for ME.

[K.L. Davis]

One thing to keep in mind here, actually a few things... these definitons are general and not at all techical, but important to understanding some of the concerns at hand. As for the conditions of metals:

Annealed/solution/softened -- This is where the metal has been reduced to its softest point, generally by heating to a very high temp and cooling slowly. The annealed state is where most of these metals can be worked and machined.

After this, most steels are "hardened" by heating to a high temperature and cooling quickly, usually this is where the steel will be very, very hard -- but is also brittle and under stress.

After hardening, steels are "tempered" by again heating and cooling in carefully controlled settings -- tempering softens the steel and reduces internal stress.

Grade 630 (17-4PH) is a precipitation hardened, or age hardened steel... it is taken to final hardness in one step, there is no seperate hardening and tempering process. This is done by heating to lower temperatures and allowing the PH steels to "soak" there, the major advantage to this is that the hardening temperatures are quite low in comparison and the steel does not distort much when hardened -- this means less finish machining to a hardened part and retention of final work dimensions.

With "regular" stainless barrels, there is a temper range where the steel has very little impact resistance and will "shear" very easy, sadly, this range covers a big part of where the metal would have a good combination of hardness and strength for a rifle barrel.

17-4 is not new, nor are barrels made from it... they were popular with handguns for some time and rifle barrels have been made from 17-4 for as long as I have been tinkering with these things (we still owned the panama canal). As bigbore mentioned, steel manufactures do not recommend using 17-4 for applications that will expose it to temperatures over about 700(f), and like all steels, the condition will change if it is heated to within 50 or so degrees of its hardening/tempering point...

I was told this when I started looking at 17-4 as a barrel steel: "If you ask a room full of machinist, they will tell you it is the perfect steel for a rifle barrel; but, if you ask a room full of metalurgist, they will tell you it is not" -- In an applications where the overall precision of the barrel is crucial and it will not be used in an application that will expose it to high heat, it is a great steel. I would not recommend it for a "service" rifle though, as it is overly cost prohibited and there are other choices that are better and not subject to the heat limitations.

[Nitrox]

If 17-4 is not an appropriate material for a firearm that will see repeated strings of full-auto fire, why would the material be marketed to the compact full-auto crowd?

A while back I measured the barrel temp on my 11.5" M16 with a laser thermometer and it was 500 degrees after about 80 rounds. Several more mags had the barrel well over 700 degrees.

[SinnFéinM1911]

Where are you measuring the temp ? ie Chanmber / gas block ?? And what are you using to measure it ?

I was doing some test last week, and ran about 1,200 rounds though 2 rifles with 14.5 inch bbls and the temp did not exceed 400 degree's. This was a controled test w/ thermal measuring devices.

[Yojimbo]

If 17-4 is not an appropriate material for a firearm that will see repeated strings of full-auto fire, why would the material be marketed to the compact full-auto crowd?

A while back I measured the barrel temp on my 11.5" M16 with a laser pyrometer and it was 500 degrees after about 80 rounds. Several more mags had the barrel well over 700 degrees.


That's very good question that I've not seen answered, at least to my satisfaction...

Contrary to the facts that we have been shown, there are a few dealers who say that it does in fact handle heat well. However, AFAIK, no one has actually done any scientific testing and supplied any data to prove or disprove this.

BTW, what happened to Noveske forum here? I was following a thead there about the 17-4 barrels and the last thing I saw was that the barrels Noveske makes are made to condition H1075.

How much difference is there between a condition H1025 and a condition H1075 17-4 barrel? Also, how does this difference in tempering change how the steel handles heat?

[SinnFéinM1911]

Yeah, I just noticed it gone too ! ... hmmm

[K.L. Davis]

How much difference is there between a condition H1025 and a condition H1075 17-4 barrel? Also, how does this difference in tempering change how the steel handles heat?

Grade 630 is harder when hardened at lower temps, and softer at higher temps -- the difference between the two is 50*f (the condition number is the hardening temperature). H900 is the lowest hardening temp, but 630 at H900 is very hard (somewhere around woodpecker lips) and pretty much unusable for the application.

H1025 has a rockwell scale of about 38 with a tensile strength of about 1100-1200. H1075 has a rockwell of 36 and a tensile of about 1000-1100.

[Nitrox]

Where are you measuring the temp ? ie Chanmber / gas block ?? And what are you using to measure it ?

I was doing some test last week, and ran about 1,200 rounds though 2 rifles with 14.5 inch bbls and the temp did not exceed 400 degree's. This was a controled test w/ thermal measuring devices.

First off, this was certainly not a scientific test, just a "hey I wonder how hot it gets" bubba test.

Second, the measurement was taken toward the chamber (nothing scientific), just shot the laser toward the chamber end with the top handguard off. I ran an V33/HK33 at the same time and had the PC finish boiling off at 120 rounds/3 mags of rapid semi (measuring around 450 degrees).

I used the worlds most accurate temperature recording device, a Craftsman infrared hand held thermometer (http://www.sears.com/sr/javasr/product.do?cat=Mechanics+Tools&pid=03450466000&vertical=TOOL&subcat=Automotive+Specialty+Tools&BV_UseBVCookie=Yes). :D

[SinnFéinM1911]

I was not downing you, I was just curious.

God, I love my typing abilities ! !

[Yojimbo]

Grade 630 is harder when hardened at lower temps, and softer at higher temps -- the difference between the two is 50*f (the condition number is the hardening temperature). H900 is the lowest hardening temp, but 630 at H900 is very hard (somewhere around woodpecker lips) and pretty much unusable for the application.

H1025 has a rockwell scale of about 38 with a tensile strength of about 1100-1200. H1075 has a rockwell of 36 and a tensile of about 1000-1100.

How does this compare with a chrome lined CMV barrel?

[bigbore]

First off, this was certainly not a scientific test, just a "hey I wonder how hot it gets" bubba test.

Second, the measurement was taken toward the chamber (nothing scientific), just shot the laser toward the chamber end with the top handguard off. I ran an V33/HK33 at the same time and had the PC finish boiling off at 120 rounds/3 mags of rapid semi (measuring around 450 degrees).

I used the worlds most accurate temperature recording device, a Craftsman infrared hand held thermometer (http://www.sears.com/sr/javasr/product.do?cat=Mechanics+Tools&pid=03450466000&vertical=TOOL&subcat=Automotive+Specialty+Tools&BV_UseBVCookie=Yes). :D

Its the temp at the throat/chamber I'm concerned with. If your barrel doesnt foul, and and looks great, but your throat is burnt out your, accuracy at distance wont be $hit. If the throat gets hot, and goes to $hit on a 11" barrel you are only shooting at 25-50 yards who cares? Maybe its a worth while trade off in some applications?

[twl]

If "hardness" was such an issue, then why wouldn't a chrome-lined barrel, which has at least double the hardness of the Noveske 17-4, last practically forever?

You don't "wear down" the rifling lands in a barrel to the point of the barrel "wearing out". The throat burns out.

Barrel steel erodes from the blast of firing, and it erodes faster with increased heat.
If you want a longer lasting barrel, then use a design which manages heat better. Not a harder Rockwell number.

Or, you could just shoot at a slower pace, letting the barrel cool between shots. Or you could shoot at a slower pace on cool days.
Anything that reduces the barrel heat, will help improve its life.
Using calibers that are "barrel burners" such as some big magnums and severely necked-down large capacity cases, will shorten life, even under ideal conditions, compared with a more moderate cartridge.

Heat, heat, heat.
That is the concept that must be dealt with when talking about barrel life.

[jmart]

Are some of the questions posed here really realistic? My takeaway is that 17-4 can't withstand sustained FA fire, like four mags or more in a row. What applications require that level of fire? Sounds to me like the detractors are debating more from a theoretical standpoint than a practical standpoint.

Now, whether or not the advertised service life extension experienced is worth the added cost, I have no idea, that's for each user to decide.

[madryan]

I regularly machine stainless. Mostly 303 and 304 but we do a fair bit of 17-4 and 316, as well as some 416.

As stainless goes, 17-4 is tough. It machines fairly well, as in it's not gummy and abrasive like 304. I typically run about 60 surface feet for 17-4 with HSS tools and about 250 surface feet for carbide. With 304 you're looking at about 40 surface feet for HSS and about 200 for carbide. As with any stainless, coatings on your tools play a huge role in how it cuts. To cut stainless efficiently you need a big rigid machine. If you want to better visualize the difference between stainless and chromoly get a piece of each and clamp them in a vise. Take a nice sharp file and file away at the chromoly. The file will bite right in, even if it's hardened. Then take some swipes at the stainless. The file wants to skitter across the top of the material and won't bite in nearly as well. 416 is the only stainless that's actually easy to cut.

416 which is what most stainless gun parts are made from is really free machining as stainless goes. It is heat treatable, and fairly tough. I'd say that it's better for an application such as barrels, but we have made gas blocks for a certain AR parts manufacturer out of 17-4, which is probably ideal.

We have another customer who flies and maintains a fleet of large Helocopters and we make tons of stuff for them. All of it is made from 17-4 if it's a structural part, and 7075 aluminum if it's a non stressed part.

If you want good heat resistance you can use Inconel, or Kovar, but both are fairly soft and have so much nickel and chrome in them that they're a bitch to cut. You eat tools up all day long.

I'm not a metalurgist, but we do have a metalurgical engineer working for us. I could ask him what he thinks. He's a gun fanatic and has probably forgotten more about guns than I know.