Barrel burnout

[Mikecr]

But just were does the barrel burn?

It isn't really a burning/erosion, that leads to a normal [loss of accuracy point] from a barrel.
The normal cause is carbon impingement to a point of constriction.
There is some point, some distance down a bore, where carbon works it's way into the metal. It's just the right temperature and carbon state to condense into the metal surface, right at that region. What's the word,, precipitate?
Bullets have to squeeze through it, and then they're relatively loose for the rest of their travel.

This distance & timing varies with all that's going on from your load and shot timing, but nobody has ever escaped it. All barrels reach an endpoint of peak accuracy, and it's usually a step change. Those actually reaching and following cutting edge accuracy can see the change right to the particular shooting session. Those that never reached peak accuracy from a barrel, will not even notice it's demise.

If you don't manage carbon well a temporary constriction can build, which you can outright feel with a tight patch. This can be removed with a short stroking of J-B non-embedding bore cleaner. If the constriction is a moly ring precipitation, you can forget it right there. The fix is too damaging. Game over.
It might seem like regular but mild fire lapping could mitigate eventual constriction, but I have tried this with variance across 3 barrels of the same chamber, and it did not change accurate barrel life at all.. It's like if you open the constriction, well now you've created a rough patch (friction point), that again messes with the load results.

None of my barrels have exhibited bad throat erosion at end of accuracy. That's not it.

 

[nuclearmonkey]

It isn't really a burning/erosion, that leads to a normal [loss of accuracy point] from a barrel.
The normal cause is carbon impingement to a point of constriction.
There is some point, some distance down a bore, where carbon works it's way into the metal. It's just the right temperature and carbon state to condense into the metal surface, right at that region. What's the word,, precipitate?
Bullets have to squeeze through it, and then they're relatively loose for the rest of their travel.

This distance & timing varies with all that's going on from your load and shot timing, but nobody has ever escaped it. All barrels reach an endpoint of peak accuracy, and it's usually a step change. Those actually reaching and following cutting edge accuracy can see the change right to the particular shooting session. Those that never reached peak accuracy from a barrel, will not even notice it's demise.

If you don't manage carbon well a temporary constriction can build, which you can outright feel with a tight patch. This can be removed with a short stroking of J-B non-embedding bore cleaner. If the constriction is a moly ring precipitation, you can forget it right there. The fix is too damaging. Game over.
It might seem like regular but mild fire lapping could mitigate eventual constriction, but I have tried this with variance across 3 barrels of the same chamber, and it did not change accurate barrel life at all.. It's like if you open the constriction, well now you've created a rough patch (friction point), that again messes with the load results.

None of my barrels have exhibited bad throat erosion at end of accuracy. That's not it.

So how often are you keeping carbon in check?.. I'm assuming that if allowed too long between cleanings it becomes buried underneath layers of copper. I've spoken to a few builders who mentioned when their barrels shot out it was a sudden and immediate loss of velocity. I'm still nursing my rifles along, but am always interested in prolonging barrel life best as possible considering how terrible I am at load development!

 

[Mikecr]

So how often are you keeping carbon in check?..

I was taught at an early age to put away guns cleaner than pulled.
With this, my guns are managed as pristine. If I shoot only one shot, I still take the bore to white metal clean and then dry pre-foul it before putting away.

This does not hurt barrel life,, but it does not help either.
The carbon that kills barrels is NOT what we clean out. You can't see it with a borescope.
I have high hopes for melonite treatment,, perhaps closing of metal surface pores, but we'll see.

As far as I know, nobody has ever managed to extend accurate barrel life.
When you see crazy declarations of barrel life at like ~4K rounds, just recognize that their gun is only -still shooting good. That doesn't mean that it has not gone past it's peak accuracy potential. It just means that it's still shooting good enough.

But when you're used to a certain level of result, and at ~1850 rounds that result suddenly opened 1/8moa, and 400 rounds later you couldn't get it back? It ain't ever coming back, and you just need to get used to that. Stop tail chasing.
It's possible to plan for it, to recognize it, and have another barrel in the waiting. The competitive among competitors know this for sure.

If interested, I can send you an accurate barrel life spreadsheet that has not let me down yet. I just can't attach it here..

 

[Lefty7mmstw]

They look something like this when shot out…from the throat forward….
View attachment 363549

looks like the 7rum barrel I pulled and tossed below my bench a couple years back...first couple inches were nearly burned flat...

 

[Lefty7mmstw]

Carbon impingement might actually destroy accuracy in some barrels, whereas some like my 243 and 7rum shot until I could no longer get a decent measurement on the rifling origin. That tells me there was nearly zero depth to the lands and the bullets were skidding upon engraving, much as we see in cast bullet shooting when we exceed the strength of the alloy.
I suspect the carbon buildup is different depending on cleaning methods also. I gave up on taking it easy on barrels using just chems and a nylon brush when I had severe carbon buildup in a couple of overbore rifles. Now I use a fresh or nearly fresh bronze brush, hoppes, tight fitting patches, and a heck of a lot of elbo grease to "feel" the condition of the bore. I burn the copper fouling when necessary, with Barnes solvent or a couple of others I have.
I really need to get another strain gauge setup as the restrictions and origin condition should be apparent as the barrel ages. I haven't had a strain gauge since 2004.

 

[Hugnot]

This sort of indicates why my 6mm-06 quit before my 6mm Creedmoor.

From Accurate Shooter

"Looking at those two factors, we can express the 'Overbore Index' as a mathematical formula — the case capacity in grains of water divided by the area (in square inches) of the bore cross-section. This gives us an Index which lets us compare various cartridge designs."

My thinking is:

Lots of short duration but intense heat combined with particle blasting like primer & powder residues - heat, oxidation & some abrasion in an acidic environment from burning nitrates. The 6mm -06 required 4-6 minutes between shots at 45 F to group within 1 moa at 300 and that was only for the first 5-7 shots - like look at birds & stuff thru binocs waiting for barrel to cool. Enough to erode 416R stainless. An index value of 900 should be good for barrel wear, over 1000 not so good - from Accurate Shooter. The erosion is evident from removed barrel steel. The spread sheet ^ makes no provisions for different powder burn temps. The igniton temp for any carbon is 1292 deg F, at that point any carbon would be transformed into carbon dioxide. Internal surface barrel temps would exceed that but would be of extremely short duration. The chrome in stainless steel forms an oxide that is protective, like chrome oxide that coats internal surfaces.

I like to use foaming bore cleaner followed by nylon brushing with a light viscosity synthetic motor oil & JB when cleaning rifles. Carbon, if present, is insoluble, including strong acids. Clean up any residual motor oil with 91% isopropyl alcohol when done for that 1st shot thru a clean bore. Increased heat would increase pressure & velocity.

 

[nuclearmonkey]

I was taught at an early age to put away guns cleaner than pulled.
With this, my guns are managed as pristine. If I shoot only one shot, I still take the bore to white metal clean and then dry pre-foul it before putting away.

This does not hurt barrel life,, but it does not help either.
The carbon that kills barrels is NOT what we clean out. You can't see it with a borescope.
I have high hopes for melonite treatment,, perhaps closing of metal surface pores, but we'll see.

As far as I know, nobody has ever managed to extend accurate barrel life.
When you see crazy declarations of barrel life at like ~4K rounds, just recognize that their gun is only -still shooting good. That doesn't mean that it has not gone past it's peak accuracy potential. It just means that it's still shooting good enough.

But when you're used to a certain level of result, and at ~1850 rounds that result suddenly opened 1/8moa, and 400 rounds later you couldn't get it back? It ain't ever coming back, and you just need to get used to that. Stop tail chasing.
It's possible to plan for it, to recognize it, and have another barrel in the waiting. The competitive among competitors know this for sure.

If interested, I can send you an accurate barrel life spreadsheet that has not let me down yet. I just can't attach it here..

That'd be great if you don't mind! I'll PM you my email. I'd also imagine how quickly your string of fire is also plays into account. I've got a carbon bartlein on a hunt gun that's always been allowed to cool (while I curse at how crappy my shooting is for that gun)… after 250 rounds I re-measured where the lands were and it had only eroded about 5 thou. This is on a very hot 300 WM.

With cleaning down so deeply each time, do you have issues with your first few shots while the barrel is fouling in? I notice considerable velocity increase after about the first 3 shots - enough to change the required dope.

Appreciate it!

 

[Greyfox]

I have followed the same practice as MikeCR when cleaning rifles. After cleaning, I will apply a light coat of oil, preferring Montana Bore Conditioner. From a clean barrel it can take 3-5 shots to stabilize velocity and my original zero. Un-checked, over time and shot count volume, carbon will build-up will develop in two areas…..A carbon ring in the throat, and, as a carbon slick running one half to two thirds down the length of the barrel. The carbon ring in the throat tends to be more problematic. This will be hard carbon, will not show up on your Lilly white cleaning patches, and is hard to see without the use of a good bore-scope. The effect on shooting can be a gradual increase in velocity(pressure), and/or accuracy loss. To keep this hard carbon build up in check, I will ALWAYS clean with a quality bronze bore brush(Dewey) and carbon solvent like BoreTech Carbon solvent. Avoiding the build-up from the beginning is the best way to keep the carbon build-up in check. If carbon build-up is evidenced, a thorough scrubbing with a bronze brush(with BoreTechCR) along with some JB Bore Paste on a tight patch will get rid of the carbon. With my high precision LR hunting rifles, after barrel break-in, I will take an initial accurate measurement of my throat(BTO). I will take this measurement, check for any fire-cracking into the lands, and test accuracy every 300 rounds or so, keeping accurate count of the number of shots down the barrel. When shooting, I will never let my barrel get beyond slightly warm to the touch(this is a very different approach compared to my competition rifles). Shooting HOT can reduce barrel life by as much as 50%! While I replace barrels on my competition rifles quite frequently, I am loathe to do this on my go-to, finely tuned and well understood +1000 yard hunters. This approach does work for me. Shooting 6.5x284's almost exclusively for LR hunting for quite some time, I have rifles with over 1000 rounds down the tube with no material increase in throat erosion(BTO) or loss of shooting performance.
Example; 2022vs2011, 200 yard accuracy of my 11 year old Cooper 6.5x284 with 1017 rounds. No change in MV or accuracy.

 

[antelopedundee]

They look something like this when shot out…from the throat forward….
View attachment 363549

Which brand of borescope is that? That is a really nice picture.

 

[Greyfox]

The picture I posted wasn't a bore scope photo…it was a cross-sectioned barrel photo …
I have used a Lyman Bore Scope for many years, but more recently acquired . a Teslong on Amazon. IMO, It's a better scope for the $. Lower cost models are available if you use your own smart phone for a camera.

 

[nuclearmonkey]

I have followed the same practice as MikeCR when cleaning rifles. After cleaning, I will apply a light coat of oil, preferring Montana Bore Conditioner. From a clean barrel it can take 3-5 shots to stabilize velocity and my original zero. Un-checked, over time and shot count volume, carbon will build-up will develop in two areas…..A carbon ring in the throat, and, as a carbon slick running one half to two thirds down the length of the barrel. The carbon ring in the throat tends to be more problematic. This will be hard carbon, will not show up on your Lilly white cleaning patches, and is hard to see without the use of a good bore-scope. The effect on shooting can be a gradual increase in velocity(pressure), and/or accuracy loss. To keep this hard carbon build up in check, I will ALWAYS clean with a quality bronze bore brush(Dewey) and carbon solvent like BoreTech Carbon solvent. Avoiding the build-up from the beginning is the best way to keep the carbon build-up in check. If carbon build-up is evidenced, a thorough scrubbing with a bronze brush(with BoreTechCR) along with some JB Bore Paste on a tight patch will get rid of the carbon. With my high precision LR hunting rifles, after barrel break-in, I will take an initial accurate measurement of my throat(BTO). I will take this measurement, check for any fire-cracking into the lands, and test accuracy every 300 rounds or so, keeping accurate count of the number of shots down the barrel. When shooting, I will never let my barrel get beyond slightly warm to the touch(this is a very different approach compared to my competition rifles). Shooting HOT can reduce barrel life by as much as 50%! While I replace barrels on my competition rifles quite frequently, I am loathe to do this on my go-to, finely tuned and well understood +1000 yard hunters. This approach does work for me. Shooting 6.5x284's almost exclusively for LR hunting for quite some time, I have rifles with over 1000 rounds down the tube with no material increase in throat erosion(BTO) or loss of shooting performance.
Example; 2022vs2011, 200 yard accuracy of my 11 year old Cooper 6.5x284 with 1017 rounds. No change in MV or accuracy.
View attachment 369941View attachment 369942

So much info to process!!

So I've seen some of Cortina's videos where you can clearly tell carbon layers are embedded underneath (and over top) of copper layers. Are you removing the copper to get to the lower layers of carbon, or are you only attacking the carbon that is on top of the last layer of copper?

I've also spoken to some guys who will run a bore snake thru their gun right after shooting to keep the carbon somewhat in check but keep the rifle fouled (these are military guys fwiw).

Of curiosity, how are you cleaning your throat?

Thanks for the info!! - really good stuff!! Nice to be back over this way and not just lurking!

 

[Greyfox]

So much info to process!!

So I've seen some of Cortina's videos where you can clearly tell carbon layers are embedded underneath (and over top) of copper layers. Are you removing the copper to get to the lower layers of carbon, or are you only attacking the carbon that is on top of the last layer of copper?

I've also spoken to some guys who will run a bore snake thru their gun right after shooting to keep the carbon somewhat in check but keep the rifle fouled (these are military guys fwiw).

Of curiosity, how are you cleaning your throat?

Thanks for the info!! - really good stuff!! Nice to be back over this way and not just lurking!

The process/solvents I describe clean both the copper and the carbon. To clean the carbon ring near the throat, In the addition to full length cleaning with a bronze brush, I will also short stroke the the throat area with JB Bore paste on a tight fitting patch, checking progress with the bore scope. As mentioned, avoiding build-up in e first place is the smart/easier approach.

 

[Mikecr]

With cleaning down so deeply each time, do you have issues with your first few shots while the barrel is fouling in? I notice considerable velocity increase after about the first 3 shots

After cleaning, I wash the barrel with alcohol, and when dry, I dry pre-foul with a burnishing of tungsten (WS2).
This assures that my first shot will be as good as any to follow.
I store all guns, including handguns, tungsten dry pre-fouled.

 

[nuclearmonkey]

After cleaning, I wash the barrel with alcohol, and when dry, I dry pre-foul with a burnishing of tungsten (WS2).
This assures that my first shot will be as good as any to follow.
I store all guns, including handguns, tungsten dry pre-fouled.

That makes sense. And you're seeing shots remain consistent? Gonna try this with a lab radar - definitely intrigues