Freezing a barrel ?

[StraightPipes]

This Cryo stuff has been around and discussed often. Cryo treating milling tools, engine parts etc. has been said to improve and lengthen run time greatly.
Well, lets take a "cut" rifled barrel and freeze it. What do we end up with after another cost? Many cut rifled barrels are not "stress relieved" because there is "0" stress induced during the rifling process. Button yes, cut no? I have read that John Kreiger stated that the Cryo process doesnt make a difference on his barrels, but he does offer the service.
Now the question I have; if the cut rifled barrel is basically stress free and "straight" when completed, is it going to be stress free and straight after the Cryo process?
Part 2 of question; if it is still stress free and straight after freezing, is the process going to improve "throat erosion"?

If I can have a stress free, cut rifled barrel that is straight when finished that will have maximum throat life it would be worth the extra cost to me.

Am I truly anal here or can this happen?

 

[Greg110]

Not anal, let's just say a little more esoteric than necessary. For barrel and throat life, there seems to be some promise for a salt bath treatment of some sort of nitride, I beleive. Do a search here and you will find what you're looking for.

 

[watercam]

I have cryo'd two factory hammer-forged barrels and they did seem to shoot better and clean a bit faster. No idea regarding barrel life yet. I don't think it's worth the time and expense for a custom barrel regardless of it being cut or button personally. They shoot well and clean fast anyway.

 

[fdshuster]

StraightPipes: I had a stainless Hart barrel cryo treated (22-250, 1-14), and found no advantage what-so-ever: Easier to clean? No, cleaning was never a problem, before or after. More accurate? No, always was consistantly sub moa. Longer barrel life? No, the barrel was still shot out and had to be replaced at a documented 2350 rounds fired, close to the round count of other 22-250's of mine. If able, check out an article by Kevin Thomas in the September 1998 issue of "Precision Shooting", titled " 17,224 rounds later"/ the number of 308 rounds fired in very controlled testing comparing cryo vs. non-cryo. You read, you decide. On Hart barrels web site, under FAQ, read the findings of the metallurgist's from Crucible Steel regarding 416R stainless, what many of our barrels are made of, and finally from Armalite's FAQ, page 60: "Does cryogenic treatment of barrels help in any way"? Again, you read, you decide. Just my personal experience.

 

[msnations]

416 stainless (a martensitic steel) must be cooled at a controlled rate to obtain a homogeneous crystalline pattern (martensitic transformation). If incorrectly cooled, a cryo treatment can correct anomalies (residual austenite becomes unstable below a certain thermal energy). The steel is probably so good from the mill it doesn't matter.

Something to consider: If there are grain anomalies in the steel, cryo treatment will cause irregular volumetric changes to the sample - so the only time it should ever be done is when the barrel maker receives blanks from the mill.

 

[GerryM]

Jerry hart, told me it was a waste of money on his barrels.
They are made from crucible k 416 R
They are button Rifled. and stress relieved.

 

[StraightPipes]

Thanks for answering fellas.

Appreciate the "read this" info, thanks again.

 

[glo]

I just wanted to add this to the discussion if it wasn’t already clear as to why “freezing” a stainless steel (416) barrel is a wastes of money.

One, the crystalline structure of 416 will not changed with heat. Two, 416 is corrosive resistant. Three, 416 machines better. This means as the barrel heats up it will not change shape and string your bullets all over the target. 416 is extremely corrosive resistant. During the cleaning of your barrel the ammonia in your barrel cleaning solution will have little to no effect on the barrel. 416 machines very smoothly. This will leave very smooth and uniform lands and grooves with little or no polishing needed. Due to less friction caused by a smoother barrel, bullets will foul less and barrel clean up will be easier.

However, if you are shooting chromium-molybdenum (41xx) barrel, heat will affect its accuracy. The crystalline structure of 41xx will change with heat. This is called “memory”. And as my gunsmith, James Hoag says, “Chrome-Moly has memory like an elephant.” The correct cryogenic treatment of a 41xx barrel is not a waste of money. The cryogenic treatment of a 41xx steel will stabilize its crystalline structure. 41xx is not corrosion resistant. Every time you clean a 41xx barrel it is damaged. 41xx steel is an extremely tough alloy and its machine ability is about half that of 416. All new 41xx barrels should be cleaned with soap and water then scrubbed with bore cleaner. 41xx barrels will also benefit from polishing.

Both 416 and 41xx barrels will benefit from nitriding. The only reason 41xx barrels will benefit more (even though it is tougher steel) from nitiriding than 416 barrels is the rougher inside. If both a 416 barrel and 41xx barrel start out the same than the 41xx will benefit more. The nitride process will make the inside surface of the barrel harder. A harder surface will tend to make a barrel last longer. However, if the barrel inside is rough as sand paper and you nitride it, your accuracy will suck for that much longer.

All things being equal a 416 barrel will out perform a 41xx barrel just due to its machine ability (smoother lands and grooves) and stable crystalline structure (no memory). Does that mean a noodle thin, 416, Remington barrel will out-shoot a #6, 41xx, Hart barrel? No!

 

[msnations]

Its pretty obvious that 416 is some great stuff to make barrels out of. Some thoughts though: 416 is actually less corrosion resistant than more common austenitic steels. I've seen 416 barrels rust significantly - in extreme cases. 416 also exhibits a ductile-brittle transition at low temperatures. I've never heard of barrel failure due to brittle fracture, but I think its interesting. The brittle-ductile transition is caused by the same lattice strains that eventually (at very low temperatures) cause the martensitic transformation of the grain structure that results in stress relieving.

Regardless its pretty obvious that cryo treating barrel steel has little-no effect on groups on target.

Nitriding barrels is really much more interesting. I saw an article by John Whidden a while back, but haven't seen anything from anyone else...

 

[glo]

I too have wondered how long will a barrel last before the chamber cracks. Most rifles see between 2000 and 4000 rounds before they are shoot out. My skeet gun has 8000 rounds through it. I would have to believe that the big manufactures have tested their barrels. Just think of how many rounds must go through a test barrel. Maybe it takes 50 or 100 thousand cycles to fatigue a barrel.

I have yet to see what the Rockwell hardness of a nitrided barrel is but if it’s anything like the cams and cranks I’ve had done over the years I would expect it to be around 75. I think the only place that really needs to be hardened would be the leade and neck area.

Let’s see, if you really got a good nitride job and the hardness of the internal barrel surface got up to 90, could that be too hard? Could you then promote premature fatigue falure?

As for corrosion resistance of 416, I have seen the faint remnants of rust on my Pac-Nor barrels. I’m lazy about oiling them in the off season. At least it wipes right off with no visible signs of pitting. But I bet under a microscope it’s visible. I don’t know but some of the 300 series SS like 316L look to be better a better alloy than 416. Maybe it’s the cost.

Maybe some barrel blanks are made of other 200, 300 or 400 series SS and we are just not told. To the world at large and from the big picture stainless steel is really just stainless steel.

 

[chino1969]

For any of the match grade barrels, cryo treating is a waste of time and money. Spend your money on powder, primers and learning how to shoot properly.

Lou Baccino

 

[GerryM]

Is the nitride the same as the jteck hardining system.
I have seen jtech make the barrel double it's life.

 

[Robert]

I too have wondered how long will a barrel last before the chamber cracks. Most rifles see between 2000 and 4000 rounds before they are shoot out. My skeet gun has 8000 rounds through it. I would have to believe that the big manufactures have tested their barrels. Just think of how many rounds must go through a test barrel. Maybe it takes 50 or 100 thousand cycles to fatigue a barrel.

I have yet to see what the Rockwell hardness of a nitrided barrel is but if it’s anything like the cams and cranks I’ve had done over the years I would expect it to be around 75. I think the only place that really needs to be hardened would be the leade and neck area.

Let’s see, if you really got a good nitride job and the hardness of the internal barrel surface got up to 90, could that be too hard? Could you then promote premature fatigue falure?

As for corrosion resistance of 416, I have seen the faint remnants of rust on my Pac-Nor barrels. I’m lazy about oiling them in the off season. At least it wipes right off with no visible signs of pitting. But I bet under a microscope it’s visible. I don’t know but some of the 300 series SS like 316L look to be better a better alloy than 416. Maybe it’s the cost.

Maybe some barrel blanks are made of other 200, 300 or 400 series SS and we are just not told. To the world at large and from the big picture stainless steel is really just stainless steel.

glo,

75 or 90 Rockwell 'C' ??? Are you sure of the values you mention?
R.C.C

 

[msnations]

nitrided steels usually come out 70-90 Rockwell C. Whidden's article mentions 800-1500 Knoop hardness. Its sketchy to translate between hardness scales but that's ROUGHLY 60-85 Rockwell C. That's a broad range includes most steels, and 416 will likely fall somewhere in the bottom half of that range. Its interesting that Whidden mentions the first barrel he sent off had at least a few round down it. I wonder if it would be better to send off a newly finished barrel or to break it in first...

GerryM - j-tex is something different. If I remember correctly its an electroplating process designed to improve fatigue performance by closing micro cracks in the materials surface. I don't think it actually penetrated the surface at all - so it wouldn't effect hardness much. I believe speedy G had success with it, but as far as processes go, it seems to me that salt bath nitriding would be superior for rifle barrels.

 

[frankgreen]

I read with interest! A lot of unanswered questions. Some answers are good and some not so good.

Cryo does not guarantee better accuracy. It does not guarantee better cleaning or longer barrel life either.

Yes it might make the barrel more stress free. Several factors here to consider. How do you know let alone the barrel maker know how stress free the material is to begin with. The more stress free it is the less the cryo will have an effect on it.

Second of all the comment made about that so and so uses 416R from Crucible etc....button rifling induces a lot of stress into the blank. Yes they have to restress relieve the blank again but usually the blanks still retain stress. More than you think.

We use Crucible as well. So what is being said?

Chrome moly being effected by heat more? Where did that come from and where is the proof. I have not seen this anywhere. I myself have 5 c.m. barrels on my match rifles and they don't shoot any different than a s.s. barrel.

We even have made c.m. barrels for short range bench shooters. The most recent was for a shooter on the west cost because he wanted his barrels blued to match his BAT action. The guns/barrels are winning matches etc....it's going to be hard to tell him something different.

Also the vast majority of the test barrels we make are made out of c.m.

When I see the test data from 9 barrels in .300 Win. mag in the last year and all are c.m. shooting factory loaded match ammo and at 600 yards shooting consistently around 1/2 moa out of a 50 year old accuracy rest. The s.s. haven't shot any better out of the same set up. And they beat the hell out of them. How about 300 rounds in the first 8-10 hours on the first barrel. If there was a problem with heat and c.m. you think it would've shown up right here.

The Nitriding thing we are watching as well.

Good reading guys. Keep it coming. This is how we learn.

Later, Frank
Bartlein Barrels

 

[fdshuster]

frankgreen: The claims of "better accuracy, easier barrel cleaning, and longer barrel life" were all part of the advertising claims made by "300 Below Zero", not too different from the hype being made today for other products & services. Not saying at least some of them are not true, but some of them also are not.

 

[msnations]

The Pearlite present in 41xx steels at room temperature is converted to gamma iron (Austenite) at about about 700* C - when 41xx steels are glowing a faint red . I wouldn't worry about that under 'normal' shooting conditions.

I understand from John Krieger that a lot of the preference for 416 barrels dates back to the 60's when stainless steel blanks were more homogeneous than chromoly. Now, he says, its hard to tell the difference.

EDIT: A quick comparison of 416 and chromoly steels (as relevant to barrels):

1. They have similar density and moduli of elasticity, so barrels will have similar weights and stiffness.
2. chromoly steel has about 60% greater thermal conductivity than 416, so it will sink heat away from the bore significantly faster (great for machine gun barrels!!)
3. In the annealed state 416 is 33% harder than chromoly. However, I'm uncertain how barrel makers prefer their steel to be tempered by the mill. For reference, after nitriding, the surface will be 2-4 TIMES harder than the base barrel steel.
4. 416 steel exhibits approx. 25% less thermal expansion than chromoly steel across the 'normal' operating temperature of a barrel. Keep in mind than when a hot barrel 'expands', it actually shrinks the nominal bore size. A quick example: for a 416 Stainless steel, straight 1.25" OD, 6mm barrel, the bore shrinks (VERY) approximately 4.2e-7 inches per degree C. How hot your barrel gets really depends on a bunch of variables, so plug your own temperature in.
5. We all know that chromoly is highly susceptible to corrosion, where 416 is significantly better...

I'm sure I've left out a bunch of stuff, but those properties are what came to mind first...

 

[frankgreen]

Yes I agree with the comment that the quality of the steel between c.m. and s.s. is much harder to tell now a days. Yes the c.m. is less corrosion resistant as well. In the grand scheme of things as far as accuracy goes I don't think there is a ton of difference that anyone can really pick up on anymore.

Also going back to the heating up and causing accuracy problems. The example I gave with the .300 win. mag. is true. They have to shoot 10 rounds for groups, I believe it is 30 rounds per lot and 90 rounds in between cleaning and there is a time limit they have to do it in to use the data. The barrels do get warm/hot.

We haven't forgotten about the steel issues Krieger went thru and what we learned also in the years we worked there.

Later, Frank
Bartlein Barrels

 

[therifler]

i agree with frank freeze your hammer forged or chromoly leave the s.s match grade barrels alone . by the way frank still winning with one of your 6.5 barrels i chambered in 6.5 250 ack. 1800rounds no frost treatment just good barrel making .thanks the rifler mike burns

 

[StraightPipes]

Gentlemen, again this is some great knowledge we have here. If I read and understand these statements correctly, the Cryo treatment "does not" offer any noted benefits to our match barrels. If there are benefits, they arent worth noting.

That said, can this question be answered?
Do "CUT RIFLED" barrels need to be "stress relieved" after the rifling process ? Or, do some cut rifled barrel builders stress relieve where some do not?