Muzzle Coppering?

[VooDooMagic]

So what is your understanding\explanation for the occurance of exaggerated copper fouling at the muzzle? Why more at the muzzle? I've got a barrel that copper fouls visibly for the last two inches at the muzzle, so if I cut two inches off will it stop copper fouling at the muzzle or will it just move back down and still foul the last two inches? I'm curious to hear what others have experienced or have to say about this. I have had some lively discussions with my local crowd about this and everyone seems to have a different understanding of this common phenomenon.

 

[spdfreq]

had the same thing but it was from a bad magna port job taking off the end of the barrel was my only opions

 

[jonbearman]

I would give it a thorough cleaning with a heavy duty copper solvent (remember dont leave any copper solvent in any longer than 10 mins if it has ammonia in it),Then I would use jb bore paste and follow the instructions.Then take it to a reputable gunsmith who has a good borescope and have him check the whole lenth. You didnt say if you had a stock barrel or a highend barrel.What caliber and what bullets you use.Are they factory loads or hot handloads.Do you use a bore guide or do you clean from the muzzle.What kind of cleaning rod are you using(aluminum,brass,coated,stainless brush or brass). Give us more imfo so we can point you in the right direction.

 

[VooDooMagic]

It is a question of the basic phenomenon, of more build up at the muzzle, not one of "bore fouling" throughout. Nor one of a specific brand bullet in a specific brand barrel. Why is it heavier at the muzzle?

 

[RonAKA]

The velocity is obviously highest near the muzzle. I've never tried to figure out where the copper is. I just clean until it is gone. My Savage LRPV does not copper foul and hardly ever see the slightest trace of blue on the patches. But, another barrel of unknown origin I have copper fouls badly. I just keep cleaning and soaking until it is gone. Takes probably 15 patches compared to 1 or none with the Savage.

 

[shortgrass]

If it's coppering at the muzzle it's probably collecting copper in its full length. Those first 2 inches are just what you can see with the naked eye. Bore scoping will tell you for sure.

 

[Tozguy]

Its just a theory but here goes anyway. The surface of a bullet heats up as it travels the bore. The longer the bore the more it heats up. The hotter the bore the faster it heats up. Because of the very short time involved, the bullet jacket does not have time to transfer the heat away from its surface into the body of the bullet. A few molecules of copper on the surface of the jacket eventually get hot enough to melt before exiting the barrel and smear on the rifling near the muzzle. This usually shows up on top of the rifling as opposed to in the bottom of the grooves because this is where pressure on the bullet is greatest. This implies that shorter barrels and slower shooting should reduce copper fouling at the muzzle all other factors being equal.

 

[flatlander]

Krieger's theory is that a minute amount of copper actually gets vaporized as the bullet is exiting the case. Because heat & pressure of the propellant gases decrease as they expand while traveling down the bore towards the muzzle, the vaporized copper comes out of its vaporized state and is deposited in the bore at the muzzle.

I've seen the same thing in many of my 28"-30" Bartleins & Kriegers in 6mm, 6.5mm, & 7mm. Beware of using any abrasive cleaner that polishes the bore too often - there's a reason that Bartlein, Krieger, and other barrel makers that hand-lap their barrels stop short of creating a mirror finish in their bores. If you polish a bore mirror bright, it'll actually attract more copper fouling. Better to use a good copper solvent and let it soak long enough to do the job chemically. Boretech Eliminator works fine for me.

 

[VooDooMagic]

Now we are getting more than just "skin deep" into this phenomenon with some insightful thinking. That is what I was hoping for. To expound a little on what has already been mentioned, let me ask this please. What part of a barrel is coolest after 1 shot? 2 shots? 5 shots? Constriction (actually lack of expansion) and condensation (of sorts) happening at the coolest part of the barrel...

 

[Tozguy]

Doesn't a solid like copper go through a liquid state before vaporizing?
Doesn't higher ambient pressure increase the temperature at which a liquid will vaporize? What is the boiling point of copper at 50,000 psi?

If the copper did vaporize, how could copper vapor condensate in one location in such significant quantities before it was blown out of the barrel?

Considering that throat erosion is a well documented occurence it might mean that short term surface temperatures are highest at the chamber end. If the cooler muzzle area caused condensation of copper vapor, wouldn't the bore be more evenly plated than the streaks we observe. Or, wouldn't there be more copper in the bottom of the grooves which should be cooler than the top of the rifling where copper fouling usually occurs?

 

[VooDooMagic]

The surface of a bullet heats up as it travels the bore. The longer the bore the more it heats up. The hotter the bore the faster it heats up. Because of the very short time involved, the bullet jacket does not have time to transfer the heat away from its surface into the body of the bullet. A few molecules of copper on the surface of the jacket eventually get hot enough to melt before exiting the barrel and smear on the rifling near the muzzle.

Would the cooler, smaller muzzle diameter exert more pressure on this "softened" bullet jacket and "pull" more copper off of it?

 

[KMart]

If the copper did vaporize, how could copper vapor condensate in one location in such significant quantities before it was blown out of the barrel?


To get the solid to vaporize you have to increase the heat and pressure. The copper vapor is then in the gas behind the bullet. When the bullet exits the muzzle, the temperature and pressure instantly drops allowing the copper to become a solid again.

 

[Tozguy]

Bullets are made to conform to the dimensions of a barrel. As the bullet enters the bore, the leades put much more pressure on the side of a bullet than a slight choke caused by a cooler section in the barrel. If side pressure was a factor there is no reason that I know of why a bullet would smear copper only at the muzzle and not near the throat where side pressure is greatest. EXCEPT if the surface of the bullet has melted by the time it reaches the muzzle. A slight constriction (choke) could possibly pick up the liquid copper more than a straight section would. However, the actual existence and measurement of temperature induced bore size variations such this is far from obvious.

To get a solid or liquid to vaporize, you need to increase temperature and/or DECREASE pressure. Increasing pressure diminishes vaporization. Thats how they make dry ice remember?

The gas pressure behind a bullet continues to accelerate it for around 4 inches after it has left the muzzle. The gas actually accelerates past the bullet travelling at 3000 fps. IF the copper vapor is caught up in this flow how could it all of a sudden condense, stop and stick to the bore?

 

[shortgrass]

You never have taken into consideration that this barrel my just be rough on the inside and prone to collecting copper. Having it bore scoped will end the speculation.

 

[Tozguy]

Muzzle coppering is too prevalent to be explained by an occasional rough spot. Why would so many bores be rougher at the muzzle than elsewhere? The original question is an invitation to speculate about muzzle coppering...why should we want to put a different spin on the question or put an end to it? Almost all of what we read anywhere about fouling, cleaning, breaking in a barrel, etc is speculation. Thats all we have. I too would like to see some borescope observations on the muzzle coppering that we are speculating about. It would be a big help in figuring this out.

 

[shortgrass]

I've scoped barrels that are rough from one end to the other, an "occasional" rough spot? Most factory barrels have, if not a few, many tool marks in them that easily collect bullet jacket! jonbearmans' question never has been answered here, is this a custom tube or a factory barrel? This 'vapor thing' is the different spin if bore condition has not been previously verified. As to "why would so many bores be rougher at the muzzle than elsewhere" , it's because you can't see 'elsewhere' without scoping. Eliminate the obvious first, than look elsewhere if need be.

 

[VooDooMagic]

Alright then, it is a custom barrel which scopes great. Now what...

 

[shortgrass]

Well,, nice of you to come across with some more relavent info. I've been shooting custom barrels for 35 yrs. I've been in the gunsmithing business for the last 18 (and am professionally trained, I might add). Over those last 18 years I have fitted (threaded, chambered, and crowned) hundreds of custom barrels (Kriegers, Harts, Shilens, & Broughtons ) and have never encountered this phenomenon. I've chambered some of those really high intensity cartridges that should vaproize copper easily (like the 6.5mmx.300WSM). The only time I see this is in factory barrels. Might be your barrel isn't 'scoping' as good as you think it is.

 

[Tozguy]

Voodoo, your first post titled muzzle coppering asked whether cutting the barrel shorter would eliminate the muzzle coppering you were experiencing. Obviously if we assume that the barrel is copper fouling the whole length then, no, cutting the barrel shorter will not eliminate it. I am sure you had that figured out by yourself.
It was to the acedemic side of your question asking for our explanations on why copper fouling occurs at the muzzle (and not elsewhere) that I responded to. This in the interest of determining whether cutting back a muzzle fouling barrel just might solve the problem. It is a question that I would like to have an answer for as much as you do. I have shared my thoughts here with you and my provisional answer is yes. That I ever actually put my theory into practise and cut a barrel to cure muzzle coppering is another story.
It is obviously good advice that you diagnose the problem correctly before cutting your barrel but then there is no reason for me to think you haven't.

 

[RonAKA]

Alright then, it is a custom barrel which scopes great. Now what...

Custom barrels are often lapped to leave a slight choke in the last bit of the barrel. So it may be just lapped less in this area, causing it to copper more. Cutting it off, may remove the choked part, and potentially impact the grouping.