What is the actual cause of barrel wear?
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Very well presented! For what its worth, I think you are spot on with this!
DW
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Exceeding the elasticity of the steel.
It takes time for something to stretch and flow.
Work hardening reduced elasticity.
That is in all metals that I can think of.
Brass annealing is a big subject around here.
The barrel never gets annealed to restore elasticity.
It is continually workharded and loses elasticity.
Eventually rather then stretch, the metal begins to tear at the granular level.
Once torn it never goes back.
It will not have the same strength when the next pressure spike is applied. There will be slightly greater stretching or tearing.
The process accelerates once the tearing has begun.
Next time you take a part off of a vehicle that broke look closely.
You can see the initial cracking and then see the intergranular failure as a slightly smoother area where the cracks propagates.
Finally you see the fin nasty tear where it completely failed all at once rather than the micro fissures.
Would love to see some barrels that have been sectioned, ground and polished and then under a microscope.Hardness testing would be interesting too add.
It could be like a micro quenching process.
Heat is app lied at the surface, and then it is quickly wicked away by the rest of the other conductive mass.
Quenching increases brittleness.Combine the two and fire cracking is the result.
I like your blow Torch description.
It touches on the time element.
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Makes sense.
It would bring up some interesting scenarios, and many many questions.
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One of thing. Smaller inner diameter verses larger ones.
The ratio of circumferential elongation for a given increase in diameter due to pressure spiking will be greater for a small bore than a larger bore.I would love for see how deep fire cracking goes.
It reduces the effective thickness of the pressure vessel walls allowing even more stretching.
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Metallurgy just really piques my interest.
You want a hard surface to resist wear and have a lower coefficient of friction.
Hardness is more brittle though.
We want a strong high modulus of elasticity to take the pressure spike and return to original size without permanently deforming the part.
Like going from a class 8 bolt to a class 5.
Class 8 is stronger in clamping but they don't take overloading well. They snap. A class 5 will stretch a bit.
Different metals, different heat treat, different forming methods, cut vs CHF vs button rifling, all affect the grain structure.
Nitriding has been used to add hardness without adding brittleness for parts that see constant stress reversal in use.
Different alloys handle it differently as well.
You have longitudinal stretching like a Slinky toy as well as circumferential stretching as the pressure wave moves down the barrel.
By modeling the pressure curve it may be possible to calculate an optimal taper to reduce unnecessary weight where it isn't needed.My Son starts a Solid Works program in the Spring.
I'll buy him the full student edition that has the FEA module in it.
That would be fun to play with.
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I suppose if I had payed more attention in geology class I could probably contribute more. Metamorphic petrology deals with stuff deforming under heat and pressure, and I'm sure a connection could be drawn.
I liken it as Greg said, to a dry lake bed, but the mud underneath is still wet. Thus you have hard solid dirt riding on soft mud.
In the case of the barrel you have a work hardened bore surface, on a non hardened surrounding barrel.
As it was said above they can't coexist as soon as the pressure spikes.Or maybe I'm wrong and misunderstanding this problem entirely
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This is very thought provoking. I'm gonna keep thinking on this probably for years to come.
Everytime brass is worked it gets harder. When it is annealed it returns the elasticity to the brass. We all know this and this is why we anneal.
I have the idea that steel is the opposite. I may be wrong, but I thought that steel became softer when it was worked and then hard and brittle when annealed.
If this stretching is the case (and it very well makes sense), then the stretching does not extend to the putter portion of the barrel or it would also cause the same effect on the action that held it. I think like you say...it is a combination of several phenomenon ... pressure being at the core of them.
I wonder how long a barrel would last if cleaned every round (less foreign matter introduced)
I wonder if a heavier contour barrel lasts longer (less stretching).
I wonder if a material other than copper jackets would make a difference (different coefficient of friction)
I wonder if different powders would make a difference.
I wonder if the number of lands and grooves would make a difference.
I can easily see spending in the millions preforming all of these tests. It really would be interesting.
Pistol barrels seem to last much longer...but they are less of everything (except friction). Less pressure, less heat, less velocity. That would tend to lead me to believe that it is more that friction at work.
Isn't it the forcing cone that tends to wear out on revolvers? Again...area of highest pressure combined with friction.
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I believe George at GAP has also drawn a similar conclusion.
That's kind of why the 6.5SAUM was made and coupled with h1000 to lower pressure and increase barrel life.
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Grab a steel coat hanger and start bending.
It is as ductile as possible in order to be drawn.
The bend works hardens it and it gets stronger at the bend, for a short period of time.
It rapidly fatigues and fails at the work hardening juncture to the softer metal.
Same with metal banding straps.
God knows how many of those I have had to bend to break over the years.
Caterpillar quit using metal banding straps on parts pallets for delivery.
They use a heavy nylon band to hold shipments of heavy parts together.
Less fatigue and no corrosion from being left outside.
Forgot to add that. Corrosion in the interstitial spaces of the metal.
Hydrogen Embrittlement. One reason some very high strength metals are plated before heat treating.
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It's very thought inducing for sure. I'm going through NACE in January, maybe I'll be able to add some more to this after that.
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You are correct hypo. I was wrong.
So if properly annealing steel would return the original properties...would annealing a barrel every 300-500 rounds make it last longer?
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@dddoo7 said:
would annealing a barrel every 300-500 rounds make it last longer?
There it is. I was wondering if any of you were going to ask that. ;)
I'm currently researching how to anneal stainless. :p
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I was thinking about the same thing overnight, but from an engineering standpoint.
Wouldn't annealing induce minor dimensional changes into the barrel?
I thought that's why custom actions are heat treated before the final machining process, so they don't change dimensions of the finished product.
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@ragnarnar said:
Wouldn't annealing induce minor dimensional changes into the barrel?
Right, but what would a dimensional change in a barrel show up as? POI shift, requiring a 1-time re-zero? If the theory is sound, then we would be "returning" the barrel's dimensions back to their original, not changing them to new dimensions... right?
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How many old barrels do you have to experiment with?
Also, look up sintered powdered metals.
GM has been doing connecting rods for over a decade.A part manufactured that way should return to its original state if it was damaged and went through the sintering process again.
Heat it back up and the grains flow a bit and heal the fractures.
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@orkan said:
Right, but what would a dimensional change in a barrel show up as? POI shift, requiring a 1-time re-zero? If the theory is sound, then we would be "returning" the barrel's dimensions back to their original, not changing them to new dimensions... right?
🤔 That sounds right to me....You've annealed far more things than I have and probably will, so this is a guess. I don't know anything about the thermodynamic properties of steel.
If the dimensions shift back to "new" awesome. Rezero and be done. Even if it shifts left, right, front, back, whatever it should still be good after a rezero.
I'd worry about the bore shifting in a way that's not recoverable. So a .264 bore grows to .265, or whatever the critical dimension is.
Differential cooling or something could cause one side to contract faster than the other resulting in a crooked bore or something....I think. 🤓🤔
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I would only anneal the chamber and about 6-8" of the barrel. I think at the worst you will have to do new load development...but time will tell.
Cool thing about the dta is they should be easy to anneal because they can be pulled from the action.
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Well before I try this myself, I'm going to try harder to find someone that's done it.
If I can't find that, I'll likely be waiting until spring, and then learning how to build a kiln. ;)
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What about induction? I know we have gone back and forth on this...but it seems like a very controlled way to go here and it doesn't need a 100% duty cycle either.
I think you will need to post heat it as well to keep it from getting brittle...but I'm not sure. That is just high school welding class talking as it pertained to cast iron. Stainless might be completely different.
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Suffice it to say, I'm very versed on brass annealing. ... but I don't know a damn thing about properly doing this to a barrel. Very limited understanding of what the "right" process would look like at this point. Induction sounds like a great idea... but I'd really like to talk to some of the plants that barrel makers get their blanks from.
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I imagine you'd have to stick the heating element down the bore, and do it from the inside.
You'd damn near be melting the outside of the barrel if you used one of the thicker contours and tried to go from the outside.
Failing that you'd probably have to anneal the whole barrel, super slowly and then pull it out immediately if you're going from the outside.
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@ragnarnar said:
You'd damn near be melting the outside of the barrel if you used one of the thicker contours and tried to go from the outside.
Not true. Time and temperature. Time is a critical factor. If you heat beneath the melting point, and introduce it for enough time, it will make its way through all the steel.
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Doesn't induction work through and through almost evenly?
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Yes, I think that is correct. I'm sure there's more to it than that, but I recall that induction does work differently than flame in that way.
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@orkan said:
Not true. Time and temperature. Time is a critical factor. If you heat beneath the melting point, and introduce it for enough time, it will make its way through all the steel.
I realized that as soon as I said it. I've got some vision of an induction coil with a barrel in the middle.
Won't that compromise the pressure vessel that is the barrel to go from the outside?
If you heat to whatever the annealing temp is, and leave it there long enough for the heat to move to the bore and anneal that, won't the outside of the barrel spend more time at the annealing point and become over annealed?
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Post weld heat treating and annealing for high pressure stainless tubing used in chemical manufacturing processes.
You wouldn't want say a gasoline refinery suffering any stress cracks.
That was nearly instant heat and I guess if you monitored duty cycle and current you could control temperature for as long as you needed to and then slowly step it down to avoid shock cooling or air quenching.
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Wouldn't annealing take away the heat treat, to get it back you would need to do the heat treat again. Maybe I'm wrong didn't google it even.
But if that's the case two processes would be needed, and hopefully neither would mess some critical dimension up or bend/warp the barrel.
The two processes themselves might cost more then a new barrel.
I dunno.
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Yep annealing can make the metal dead soft and completely destroy the heat treat.
There are air quenching steels. Heat treating is an art as much as it is a science.
Often times fixtures are used to hold parts during the heat treat process for something like an aircraft engine mount that is welded together from chrome moly tubing to prevent dimensional changes..Stumbled across this industry magazine...... It has some 3d Laser sintering articles. Too cool.
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Look at the rabbit hole we found to go down! ;)
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Yeah I just go the MSDS for Carpenter 416 stainless... Guess what is says.
http://cartech.ides.com/datasheet.aspx?i=103&e=79
CarTech 416 has been used for shafts, axles, gears and pinions, worms, lead screws, golf club heads, valve trim, bolts and nuts-in fact, any part requiring considerable machining. Where greater corrosion resistance is needed consider Carpenter Project 70+® Type 303 stainless, which is our free-machining 18-8 grade. CarTech 416 stainless is not recommended for vessels containing gases or liquids under high pressure.
It is easy to machine because of the Sulfur added to the alloy.
Sulfur will burn out and leave a microscopic void. Cracks begin at microscopic voids invisible to the naked eye.
I loved my Materials Science class from 24 years ago. Still have the textbook around here somewhere.
What dissolves Sulfur?Something is telling me we need a better alloy to begin with.
Looking up 410 stainless next.
A ceramic barrel would probably be ideal if it can take the pressure spikes.
Norton industries is THE go to company for Ceramics in industrial applications.410
http://cartech.ides.com/datasheet.aspx?i=103&e=82
Selection guide.
https://www.cartech.com/en/alloy-techzone/technical-information/alloy-selection
It is looking like some newer alloys have not taken hold in the firearms industry.
Never heard of Carpenter 475 Stainless or 465 utill now.
https://www.cartech.com/en/alloy-techzone/technical-information/alloy-selection/selection-of-high-strength-stainless-steels-for-aerospace-military-and-other-critical-applicationsCold working small diameters up to 20mm can result in over 300k tensile.
Wonder how strong it can be in 35 mm diameter before gundrilling?
Available in up to 12" billet.
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I've often heard a regular Chrome Moly barrel is better then Stainless, but it's a lot harder to machine.
Again never researched it.
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If that is the case then a Change in type of steel might be easier and just as effective as annealing.
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I've been down that road already.
Barrel making is part art, part science, part luck... so I know changing materials for a barrel maker would be a significant investment in time and resources. Hard to convince them they should do that when they sell every barrel they make as it is, as fast as they can make them, and often have half a year backlog.
Also difficult to convince them of it, when making barrels last longer will result in fewer barrel sales. ;)
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I've continued to think about this over the last few days.
What about the straight jacket barrel system? Litz mentions it in his most recent book.
Your barrel gets a sleeve around it then the space between the two gets filled with some compound that helps quell harmonics and wicks away heat. It supposedly helps with the pressure wave too thus extending barrel life.
There are anecdotes online about barrels that are shot out getting renewed and becoming sub moa rifles again; and about the cooling ability of the system.
Allegedly todd hodnett has a 300mag with 3500 rounds through it because the system.
The system is installed by teludyne tech. http://www.teludynetech.com/products/
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I need to look up the formula for calculating the strength of a tube in bending and resistance to internal pressure.
Increasing diameter strengthens bending resistance for certain.
Don't know what they use as a filler but it has to be rigid and noncompressible to transfer the stress to the stronger outer tube.
They will do stainless or Titanium for the outer tube.Lothar Walther does something similar.
http://www.lothar-walther.com/396.php
They are in Metro Atlanta so I could actually drive up there.
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I ran into teludyne at SHOT in 2012. Spent a good amount of time in their booth. I pressed them with specific questions, and they refused to answer. The entire thing came off as a snake-oil experience. The guy was claiming that their system would make a factory remington 700 shoot as good as any of my customs. Needless to say, I waived the bullshit flag and moved on. Thus far, no one has proved I was wrong.
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Good to know.
The heat dissipation and barrel rigidty claims seem plausible.
I can't wrap my head around the pressure aspect of their claim.
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Working with the understanding that pressure causes the metal fatigue that shows up as fire cracking, that the cracking grows progressively worse with each pressure event, sleeving the chamber area of the barrel may add strength back for the short term. Then once past the chamber area and the taper the extra diameter provides increased stiffness only it the filler medium doesn't shrink, shatter, migrate under pressure or melt and soften.
There are some ferro cement tooling mixes used for injection mold repair that might could take the pressure. A 50 ton injection molding die is 100k psi.It may work for a few dozen rounds but long term durability would be my doubts are.
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From the looks of the Lothar barrel, they are using the higher coefficient of expansion of the Aluminum trapped between two layers of slower expanding steel to lock the system together tighter the warmer it gets.
Put the barrel core in cryogenic tempering and the Aluminum sleeve in an oven for the friction fit after it cools.
Then do it again for the outer sleeve and a final cryogenic treatment for the entire assembly.
Maybe gas nitride the barrel core before the first sleeving or afterwards if it will not affect any exposed Al.They also use a different alloy than 416.
I have seen some gunsmith advertising prices that in the fine print they refuse to machine Lothar blanks.
It must be a much harder alloy.
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They allege their system cools the barrel faster. I can believe that because there are tons of metals and alloys with superior heat capacities to steel. Place any of these in contact with the barrel, and it would serve to pull the heat out of the barrel into the sleeve. Additionally, the increased diameter of the aluminum tube would expose more surface to the air thus cooling faster. Thus this claim seems plausible to me.
As for the rigidity, conventional rifle barrel wisdom dictates that a thicker barrel is more rigid than a thinner one. A straight cylinder barrel 1.25 inches in diameter should be pretty stiff. It's lighter than a traditional barrel, which should alleviate droop. Litz tests stiffness in his Modern advancements volume 2 book by hanging weights off the end of barrels; the straight jacket performs well. Therefore this seems plausible to me as well.
But I have no experience with this, just what I thought based on a science background and other anecdotal evidence.
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I won a free barrel job from Teludyne in mid 2012 and I ended up getting a 700 ADL in 243. After waiting about 4 months I got the BA back I got to work with some Berger 65 grain bullets. My load was pushing 3500 FPS which is about standard and 1500 rounds latter about a year and half it was time for a new barrel. This was used for a coyote hunting and a local varmint match. What I learned is that it will go a little longer than a Krieger MED Palma but it was never as accurate and if you wanted to set it back you were shit out of luck.
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Outstanding feedback. Thank you
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Bored at work so necro threading. Don't think barrel work hardening due to expansion is the cause. The section of barrel under stress of expansion would work harden uniformly through it's cross section. So you would see a uniform degrading of material strength.
I think it's a combination of factors.
One being surface heat of the steel under engraving forces combined with burning power flame front temperature. This is why it begins at the throat. Highest pressure as engraving begins. Now this is not causing a melting action, if it was hot enough for that the copper jacket of the bullet would melt long before the barrel steel would. Instead it's raising the surface of the steel to a temperature where it can be affected chemically. Steel can start to become susceptible to atmospheric contamination at temperatures as low as 349F depending on composition. Stainless steel is worse in that it is less thermally conductive then regular steel. So heat becomes more localized.
Another possible factor is the high pressure gas. Gasses under extreme pressure and heat can change to a state of ionized plasma. http://iopscience.iop.org/article/10.1088/0022-3727/44/27/274001
Dissimilar metals or fluids passing over metal can create galvanic corrosion. https://www.nace.org/Corrosion-Central/Corrosion-101/Galvanic-Corrosion/
https://www.bssa.org.uk/topics.php?article=89Also we have various mineral elements present in the gas stream from combustion materials.
Sorry this is not yet a finished thought, running out of time to continue this. Have to type more later.
David
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Time, temperature, and pressure often interact. The failure modes associated with each of these factors can easily be reproduced catastrophically. Shooting out a barrel is a fatigue failure.
As the bullet travels down the barrel the pressure curve returns to zero once the bullet exits the barrel. The highest pressure is observed while the vessel (barrel segment) is the smallest. The segment nearest the muzzle sees the least amount of pressure because the vessel (still obstructed by the bullet) at that point has the greatest volume.
If the material selection and barrel geometry are unconstrained in design and tested utilizing finite element analysis (FEA) we may easily double or even quadruple barrel life. Material selection (e.g. maraging steel) and barrel thickness (e.g. 6 inches in diameter at the breach) are important decisions affecting function and cost.
Try spitting without inhaling or using your diaphragm muscles. Accuracy over longer distances requires more pressure.
Guys, be proud that it is your improved marksmanship that actually shoots out a barrel. It is a wear item in our sport.
Thanks again to Greg for challenging us.
