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Chrome Moly VS Stainless Steel

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Okay guys, I need your help in edumacating myself about barrels.

I am currently shopping for a .223, I have pretty much decided on a Savage Model 12.  Either the 12BGTV or the 12BTCSS.  Both have Boyd Thumbhole stocked, fluted bull barrels. 

One is blued Chrome Moly and the other is Stainless Steel.
 
Is one material better than the other?
 
What are the pros and cons of the two materials?  Accuracy, life expectancy, wear, maintenance, break-in, thermal behavior and anything I am overlooking or totally ignorant of.  I have never owned a gun in SS so I have never really considered this question until now.  Any and all comments, opinions and observations will be greatly appreciated!
 
Thanks in advance
Bud
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Stainless obviously has better corrosion resistance, but isn't rust proof.

From a manufacturing standpoint, it's easier to get a smoother bore finish in 416 stainless than in Chrome Moly, which is one of the reasons why custom barrel manufacturers use SS for the bulk of their match barrels that are hand lapped.  All else being equal, a smoother, more uniform bore results in greater accuracy.  The 400 series martensitic stainless used for barrels is a bit more heat resistant and therefore more resistant to throat erosion, which translates to longer accurate barrel life. 
 
If you want a custom match grade barrel from one of the major players, in most cases, the decision is made for you.  Most are only available in stainless steel.
With factory barrels on factory rifles, all the above is largely irrelevent, because factory barrels aren't made to match grade standards anyway.  Good barrels can be made from either material.  In a hunting rifle, the theoretical life of the barrel is probably a moot point.  Either material will provide a long lasting hunting barrel.  For a competition barrel that's likely to see a lot of rounds, it's a different story.  Unless you do a lot of shooting, the main advantage to stainless is corrosion resistance.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/08/2009 at 08:45
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An excerpt from Dan Lilja's website (http://www.riflebarrels.com/articles/barrel_making/making_rifle_barrel.htm)
 
"The barrel maker must choose the type of steel the barrels are made from. Most often this would be either a chrome-moly steel such as 4140 or a stainless steel such as type 416. The important characteristics of the steel are its machinability, longevity, and strength. Other considerations are secondary, such as its ability to be blued or resistance to corrosion. Almost 100% of the barrels used in competitive bench rest shooting are made from stainless steel. The grades of stainless used for barrels are fairly machinable and offer a longer accuracy life over conventional chrome-moly. They are also more resistant to some of the harsh cleaners used by accuracy shooters. A side benefit is their ability to resist corrosion."
 
Have read that from a machining perspective stainless is "softer" making it a little easier to maintain close tolerances.  Stainless is also supposed to have a work hardening property that allows it to better resist throat erosion.  When under the abrasion and pressures of firing the bore and throat sections of the barrel will toughen up.
 
For a hunting application firearm a personal choice.  To be sure chrome-moly has given and will continue to give excellent service and I love the look of a highly polished blued barrel.  Climate factors where you hunt may help make the choice.
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What they said above, however:
Stainless in 416 form is not recommended for use below zero degrees.  Crucible 416R is a pre-hardened chromium stainless steel which is suitable for use in precision match-grade rifle barrels. It can be supplied in various hardness ranges according to your specific requirements ( HRC 24/28, 28/32, or 32/36). A homogeneous microstructure which responds to heat treat providing a uniform hardness. An optimum combination of high tensile strength along with adequate toughness to withstand the typical chamber pressures encountered during firing. Barrels made from Crucible 416R are used at all levels of competition and in all conditions dry, damp or salty. Although all martensitic stainless steels have reduced ductility at very low temperatures, Crucible 416R can be safely used down to minus 40°F (-40°C).

Information provided by Crucible Specialty Metals.
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Oh, I forgot to mention one other thing.  If you want a traditional blued finish, you have to use regular CrMo steel, because stainless won't accept bluing.  That isn't an issue if you're planning to leave the SS with a matte blasted or polished finish or you're planning to use a "spray and bake" or plated finish.
 
One other thing on barrel life as well...
While SS has more resistance to throat erosion, it is still softer than CrMo, so the remainder of the bore may actually have less accurate life due to friction.  So, the barrel life question may be a wash between the two materials.  Usually, throat erosion is the culprit when a barrel gets "shot out" to the point accuracy starts to suffer.  CrMo is harder and more brittle, so it is reportedly more prone to tiny thermal cracks in the throat than stainless.
 
The main reason custom match grade barrel manufacturers use 416 stainless is simply that it's easier to machine, rifle, and lap to a smooth, close tolerance, uniform bore than CrMo steel.
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And just to make things more confusing, here is an excerpt from Krieger's web site:
 

Q: Which is better Chrome Moly or Stainless Steel?

A: For the most part neither one is better than the other. The only difference we find is that sometimes the chrome moly might take a little longer to break-in and might have a little more affinity for copper or seems to show it easier. In terms of barrel life and accuracy, we can find no difference.

 
Choice is yours Bud!
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Great info guys, THANKS!!! Anybody know what material Savage uses in there SS barrels?
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I believe they are 416R - will try to verify.
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Originally posted by Dogger Dogger wrote:

I believe they are 416R - will try to verify.
 
Thank you sir!  I appreciate the assistance! Excellent
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Called Savage service line but the fellow answering had no idea.  Suggested sending a note to their engineering group.  If not a proprietory alloy could probably tell you.
 
Savage Arms, 100 Springdale Road, Westfield, MA 01085
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Originally posted by Dogger Dogger wrote:

Called Savage service line but the fellow answering had no idea.  Suggested sending a note to their engineering group.  If not a proprietory alloy could probably tell you.
 
Savage Arms, 100 Springdale Road, Westfield, MA 01085
 
Thanks for trying, I appreciate it! 
 
I have a feeling that since I have never seen anything from Savage cautioning or warning about subzero useage that they must use the Crucible 416R or similar alloy.  It would be too big of a liability issue for them not to have some type of disclaimer about their SS guns otherwise.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/08/2009 at 12:43
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A good bet that it's 416R.  Other alloys avail but probably more expensive - this seems to be the standard for US barrel makers for stainless.
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410 is actually a better stainless steel... BUT it is more difficult, and therefore much more expensive, to rife.  IF a stainless 410 barrel of high quality machining and, later, accuracy can be found, it is worth what one would have to pay for it.


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Originally posted by Kickboxer Kickboxer wrote:

410 is actually a better stainless steel... BUT it is more difficult, and therefore much more expensive, to rife.  IF a stainless 410 barrel of high quality machining and, later, accuracy can be found, it is worth what one would have to pay for it.




Yes, exactly.  410 is more corrosion resistant, but very gummy and more difficult to gun drill the blank without having gouges in the finish where the stringy chips get caught around the head of the gun drill.  Actually 416 is the same alloy as 410, just with added sulfur to make it more machinable.  Most likely 416R is the alloy of choice for most manufacturers, because it's much easier to machine than, say, 303, 316, 17-4 PH, etc.

Where I work, we machine all of the materials thus far mentioned.  Deep hole drilling with a gun drill is much easier with 416 than any other stainless.
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Ted,
 I have a technical question.  Since you work with this stuff regularly, what is your opinion of cryo-treatment of stainless steel?  If you were to cryo 410, would that resolve some of the malleability issues?  Or if you cryo 416 would that provide the addition strength, by realigning the crystalline structure, that is removed by adding sulphur?  
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/09/2009 at 10:17
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Once again I see I came to the right place to seek advice!  Thanks Dan, Ted and Craig.  I am continually impressed with the depth of knowledge and the eagerness with which it is shared on this Forum.  OT Rocks!
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Great stuff and team work!! Excellent
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  Came across this yesterday.  Don't know if it's what Savage uses in their centerfire rifle barrels but it's still intereresting.
     
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/09/2009 at 11:01
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Cool article Earl Thanks for the link!
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Originally posted by Kickboxer Kickboxer wrote:

Ted,
 I have a technical question.  Since you work with this stuff regularly, what is your opinion of cryo-treatment of stainless steel?  If you were to cryo 410, would that resolve some of the malleability issues?  Or if you cryo 416 would that provide the addition strength, by realigning the crystalline structure, that is removed by adding sulphur?  


Not sure.  Cryo treatment is a controversial topic.  From my limited experience with cryo'ed materials, I honestly couldn't tell any difference whatsoever in any physical properties of the material before vs. after.  I do know it was the hot trend in the heat treatment world about 10-15 years ago, and I see fewer people doing it or even talking about it anymore these days.  To me, that says a lot.  A couple of the prominent barrel makers say it's a bunch of hocus-pokus.  It seems to me if it really provided the benefits claimed, everyone would be doing it.  I used to have vendors visiting me claiming that if we cryo'ed our cutting tools (endmills, drills, reamers, etc.) that we'd get significantly greater tool life.  I tried it and couldn't tell any difference whatsoever.  If it worked as advertised, it seems to me all the major cutting tool manufacturers would be doing it to get an edge over their competition.  They don't.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/11/2009 at 11:30
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It is somewhat controversial.  Just wondering if you had any firsthand experience with the process. 

Studies have shown that cryogenic treatment of metals DOES, in fact, produce a realignment of the crystalline structure, thereby releaving stresses within the metal.  This can have a positive effect on metal life, especially in frictional contact situations.  In your case, where you cryoed tools and saw no increase in lifecycle use, what were the temps your tools were exposed to.  I know that some "cryo treatment" places only go down to -100 deg or so for short periods and that to be fully effective cryo treatments must go below -300deg for around 72 hours.  Some of the cryo places will have your materials back to you within 72 hours... which seems rather ineffective to me. 
I'm still doing research.  I've considered cryo treatment of rifle barrels for several years and can't find any "facts" hard enough to convince me to do it.  There is no harm done, and it is not that expensive, just can't see doing it if there is no noticeable improvement in barrel life due to reduced wear, improvement of collection of particulate matter from bullets, or some other advantage.  A Penn State University study did find a 10% reduction in austenite. 
  1. Crystal structure (sometimes called grain structure) becomes consistent or homogenous through the conversion of austenite (one type of crystal) to the desired martensitic crystal (a different shaped crystal). After heat-treating, nearly all steels have a certain percentage of austenite that was not fully transformed into martensite. This is what metallurgists call “retained austenite” or “RA”. It is widely accepted in the heat-treating industry that all heat-treated steels will have some percentage of RA and heat treatment recipes routinely specify that RA will “not exceed” a certain percentage. This can vary from processor to processor, but almost all steels have a certain percentage of RA or retained austenite. Cryogenic treatment promotes the additional transformation of RA into martensite, which is what 90% (or more) of the steel already is and the condition that is most desirable. By eliminating retained austenite (or RA), voids or imperfections in the steel’s microstructure are eliminated. This is widely accepted and well-documented fact that is evident in X-Ray and SEM (scanning electron microscope) analysis of steels before and after cryogenic treatment.
  1. The carbon structure of steels is modified through a mechanism that is technically described as “the precipitation of eta-carbides”.  While it is not fully understood why this occurs, it is undisputed that it does happen and can also be seen through SEM (scanning electron microscope) analysis of steels that are cryogenically treated versus the non-cryogenically treated steel. The population of these eta-carbides – both brilliant ones (white ones) and dark ones (black ones) – is dramatically increased after cryogenic treatment.  More information and photos can be viewed in the following technical paper, “Role of Eta-carbide Precipitation’s in the Wear Resistance Improvements of Fe-12-Cr-Mo-V-1.4C Tool Steel by Cryogenic Treatment” that was presented in 1994 at the Iron and Steel Institute of Japan. It was further documented in a paper presented at the ASM Heat Treat Conference in 2005 by Zbigniew Zurecki of Air Products entitled “Cryogenic Quenching of Steel Revisited”.
  1. All metals – not just steel, but also aluminum, copper, cast alloys, etc. – benefit from the residual stress relief that deep cryogenic treatment promotes. All metals have residual stresses; they are created from the moment the metal “freezes” from its molten form into its solid form. Molten metal freezes – or transforms from its liquid phase to its solid phase - like water or other liquids that we are familiar with. As heat is extracted through cooling, dendrites (or crystals) form from the coolest areas first. Typically, these are the surfaces and edges. This irregular freezing results in natural stress lines where the dendrites collide or along the boundaries of the remaining liquid (molten) metal and the solid metal.  After the metal is cast in it’s raw stock form, (e. g. block, billet, plate, round, etc.), it is heat treated to normalize the material and modify its properties (e.g. hardness, tensile strength, etc.). Once the raw stock is further modified, additional stresses are added  (through its machining, cutting, grinding, forging, etc.) by the manufacturing process. When combined, all of these stresses form weak areas that are prone to fail through propagation of the stress lines into cracks. These are often characterized as fatigue failures or more simply “metal fatigue”. By attacking the root cause – the residual stresses – cryogenic treatment greatly reduces or eliminates fatigue failures or cracks in metal components.

Almost everyone agrees, though, that for heat treated tool and die materials, cryogenic treatment should occur PRIOR to traditional heat treat temper that normally follows after austenizing and quenching.

 
This leads me to believe that cryo treatment must be done BEFORE tempering to be fully effective (though it does have SOME effects after).  Actually it may be best to get a blank, cryo treat it, temper it, cut it, cryo treat and temper again.  That would probably produce the greatest number of effects.
What do you think... "does the defense's case hold water?"


Edited by Kickboxer - May/11/2009 at 11:32
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I'm not saying it doesn't do anything.  All I can tell you is what my own experience tells me.  I just haven't seen enough to convince me it makes a big difference in improving the machinability or wear properties, or is a superior form of stress-relieving vs. traditional methods.  I've had one rifle barrel cryo'ed by a company called "300 Below," and I couldn't tell any difference whatsoever in accuracy afterwards vs. before.  Who knows; that may just mean that my barrel was already sufficiently stress-relieved beforehand, and so maybe it only works some of the time?
 
All of the cryo treatment vendors I've seen advertise that they do go to -300 deg.
 
I don't think I've done enough testing with cryo'ed materials to draw a conclusion one way or the other.  Personally, I wouldn't spend the money to have it done to a barrel, admittedly based on a sample size of one.
 
FWIW, here is what Shilen had to say about cryogenic treatment from their website:
Should I "cryo" my barrel?
If you have heard that the cryogenic treatment stress relieves steel, this is false. We have measured the residual stress in 4140 and 416 steel with a process called x-ray diffraction.  After much R&D, we have not been able to measure any changes in molecular stress after cryo treatment.  For this reason we do not endorse the cryogenic process, but we can safely say that it is not detrimental to the barrel either.
 
Krieger, on the other hand, is of the opinion that cryogenic treatment helps improve machinability, so they have the process done to their barrel steel.  They don't make any accuracy improvement claims, however, unlike the claims made by the cryogenic treatment businesses.
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"... and the beat goes onnn.  "   Don't get me wrong, I was just asking, I am torn on both sides of this.  One of those very difficult to pick the good from the bad.  Personally, I can't really see how it would improve accuracy, unless before the cryo treatment the steel was very soft and after had hardened some.  Decreased wear makes sense to me, but your experience seems to belie that.  More research is in order, for me.  I need to get with the metal guys here some more. 

edited to say "CAN'T see how..." which it was supposed to say before.  Sometimes my brain is MUCH faster than my fingers and finishes before my hands do...



Edited by Kickboxer - May/11/2009 at 16:57
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Cool, Thanks guys!!!  Dan let us know if you find anything more out please.
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Roger that...
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