Muzzle Coppering?
- Thread starter VooDooMagic
- Start date
Ron, that's what I thought but I didn't want to make any assumptions before replying.
When lapping a barrel the slug should not leave the bore. This will most likely leave a short section of bore at each end that is lapped less than the main section (if lapped at all). Evidence that these 'working' ends are cut off before shipping a barrel blank is that the barrel maker will claim 'land and groove tolerances' of 0.0001'' from breach to muzzle. Not much choke in that barrel blank. Do any barrel makers promote choked barrels and provide specs for them?
Further, a barrel blank is often 27 to 30'' long. If the blank is finished to say 22'' by a gunsmith for a bench gun how did the barrel maker know where to put the slight choke that you are referring to?
When lapping a barrel the slug should not leave the bore. This will most likely leave a short section of bore at each end that is lapped less than the main section (if lapped at all). Evidence that these 'working' ends are cut off before shipping a barrel blank is that the barrel maker will claim 'land and groove tolerances' of 0.0001'' from breach to muzzle. Not much choke in that barrel blank. Do any barrel makers promote choked barrels and provide specs for them?
Further, a barrel blank is often 27 to 30'' long. If the blank is finished to say 22'' by a gunsmith for a bench gun how did the barrel maker know where to put the slight choke that you are referring to?
Would the copper vapour theory people please explain a few points for us?
How does the copper jacket get hot enough to vaporize?
The boiling point of pure copper is 4653 F at atmospheric pressure. Granted, the copper alloys used in bullet jackets may vary from this boiling point. Propellant gasses have been reported by Harold Vaughn to be in the order of 5640 F. At first glance, this reflects an opportunity for the copper to be vaporized to some extent. However, there are other considerations.
The chamber pressure of say 50 000 psi would increase the boiling point considerably. How much higher would be the boiling point of copper be at this level of pressure?
Some unburned powder which is known to follow the bullet all the way out of the barrel, would act like a barrier to heat transfer. It is not obvious that the bullet would be exposed directly to the full brunt of hot propellant gases.
Even if gasses hot enough to melt the bullet actually did reach it, is the time of exposure sufficient for the required heat transfer? Could enough heat be transferred in 0.0014 seconds to bring the solid copper from around 75 F, through its melting temperature of 1981 F and beyond its boiling point of 4653 F to produce copper vapour?
If so, why would copper streaks in the muzzle be the only evidence we have of vaporization?
Why would copper vapour, if it existed, condense at the muzzle? If powder continues to burn on its way up the barrel and some even burns after exiting the bore, what evidence do we have that propellant gases are more than a thousand degrees cooler at the muzzle?
Ultimately there might very well be a set of conditions that would vaporize a bit of the copper jacket and deposit solid copper at the muzzle. It seems that these conditions would be quite unusual and far from being common enough to explain the phenomenon.
How does the copper jacket get hot enough to vaporize?
The boiling point of pure copper is 4653 F at atmospheric pressure. Granted, the copper alloys used in bullet jackets may vary from this boiling point. Propellant gasses have been reported by Harold Vaughn to be in the order of 5640 F. At first glance, this reflects an opportunity for the copper to be vaporized to some extent. However, there are other considerations.
The chamber pressure of say 50 000 psi would increase the boiling point considerably. How much higher would be the boiling point of copper be at this level of pressure?
Some unburned powder which is known to follow the bullet all the way out of the barrel, would act like a barrier to heat transfer. It is not obvious that the bullet would be exposed directly to the full brunt of hot propellant gases.
Even if gasses hot enough to melt the bullet actually did reach it, is the time of exposure sufficient for the required heat transfer? Could enough heat be transferred in 0.0014 seconds to bring the solid copper from around 75 F, through its melting temperature of 1981 F and beyond its boiling point of 4653 F to produce copper vapour?
If so, why would copper streaks in the muzzle be the only evidence we have of vaporization?
Why would copper vapour, if it existed, condense at the muzzle? If powder continues to burn on its way up the barrel and some even burns after exiting the bore, what evidence do we have that propellant gases are more than a thousand degrees cooler at the muzzle?
Ultimately there might very well be a set of conditions that would vaporize a bit of the copper jacket and deposit solid copper at the muzzle. It seems that these conditions would be quite unusual and far from being common enough to explain the phenomenon.
Regarding the correlation between bore roughnes and fouling I would say 'no contest'. Paradoxically, bores that are too smooth can also be copper foulers. It would be great to learn how to maintain the optimum level of bore roughness.
It would also be interesting to correlate barrel length with muzzle coppering.
The nice thing about naval guns is you don't need a borescope, just climb in the barrel with a flashlight
It would also be interesting to correlate barrel length with muzzle coppering.
The nice thing about naval guns is you don't need a borescope, just climb in the barrel with a flashlight
DCRYDER
Silver $$ Contributor
I too have had, and am having, this happening. Especially in my 280AI. It has a 27" Shilen Select Match barrel in a 1-8" twist. I have only been shooting 162 amaxs and 168 vlds at 2980fps. I do not own a borescope nor do i want one. I do know that my normal cleaning regiment starts with 4 wet patches of Butch's. With slow steady strokes the rod feels like it hits a brick wall 1" from the muzzle. After a few brush strokes the patch/jag slide smoothly through the entire length of the barrel. I would have to think it is related to friction/heat and is more of a galling thing.
Tozguy said:
Good points. I think if you trust the barrel maker and tell them up front the finished barrel length they should be able to do it. Krieger claims their bores are never bigger at the muzzle compared to the breech.
http://www.kriegerbarrels.com/Barrel_Making__Steel-c1246-wp3379.htm
VooDoMagic: I won't get involved in the reason(s) for the copper fouling at the muzzle: most of the causes discussed are way over my head, but I will say that I've had a couple of big name custom, hand lapped barrels that also copper fouled at the muzzle only, as seen with my Hawkeye. The rest of the bore was copper free. You did not say how many rounds have been fired with the coppering continuing to be a problem. In the barrels that had the problem, copper fouling at the muzzle gradually decreased, and in every example, was not a problem by approx. 100 rds. fired. The last fix I would consider would be to shorten the barrel---- too drastic for me. You may want to contact the barrel maker and put the question to someone who works on the barrels, ( not the person who answers the phone), and ask for their advice. 
Ron,
The Krieger site mentionned flare at the ends but nothing about choke. You are probably right that a barrel maker could put a slight choke at any point in the length of a barrel if they wanted to. Its not obvious that they would accept to even if asked. If muzzle choke is common practice and desirable for accuracy then why do we only hear about it for rimfires and not for centerfifes?
The Krieger site mentionned flare at the ends but nothing about choke. You are probably right that a barrel maker could put a slight choke at any point in the length of a barrel if they wanted to. Its not obvious that they would accept to even if asked. If muzzle choke is common practice and desirable for accuracy then why do we only hear about it for rimfires and not for centerfifes?
Tozguy said:
Choke may be a bit of an overstatement for centerfire barrels. Probably the most important thing is that they are at very most parallel, but if not parallel, then getting tighter toward the muzzle rather than the reverse. Krieger says that theirs never open up. I do believe some centerfire folk believe the barrel benefits from a choke. Here is a good article on barrel making from Border Barrels, if you have not read it before. They admit it is not unanimous that a tightening taper is better. They do suggest some barrel makers measure and grade their barrels based on how they measure. Those guys probably would be able to offer you a choked barrel
http://www.border-barrels.com/articles/bmart.htm
There is an interesting theory out there that barrel ID grows and shrinks in waves when the bullet is traveling up the barrel, and node velocities are when the bullet reaches the muzzle at a point when the barrel ID is tight. The theory is based on the thought that choked barrels shoot better. Personally I have a hard time believing the node theory based on bore diameter. I'm in the Varmint Al camp which is based on the direction the barrel is pointing at exit.
I believe this unique node theory is promoted by a member (or former member) of this forum. A link here:
http://www.the-long-family.com/OBT_paper.htm
Ron, I too found the Varmint Al explanation on barrel vibration and accuracy very credible.
As far as choke goes, it is hard for me to believe that a centerfire barrel would have choke deliberately put in for accuracy's sake. I would not be surprised that some slight unintentional choke in the bore would result from contouring it and that this is not detrimental nor beneficial considering how slight it would be. Nevertheless, wouldn't we have to measure how much choke a barrel actually has to be able to relate it to muzzle coppering?
Frank's comments on copper fouling eventually diminishing with enough firing/cleaning cycles is encouraging for me and hopefully for VooDoo too. The secret to success along these lines would be to be absolutely sure all copper is removed on a regular basis until it stops showing up. The only reliable way to know that all the copper fouling is gone before another firing is by using a borescope.
Voodoo, would it be time for you to share with us what your friends at the range came up with on your original question?
As far as choke goes, it is hard for me to believe that a centerfire barrel would have choke deliberately put in for accuracy's sake. I would not be surprised that some slight unintentional choke in the bore would result from contouring it and that this is not detrimental nor beneficial considering how slight it would be. Nevertheless, wouldn't we have to measure how much choke a barrel actually has to be able to relate it to muzzle coppering?
Frank's comments on copper fouling eventually diminishing with enough firing/cleaning cycles is encouraging for me and hopefully for VooDoo too. The secret to success along these lines would be to be absolutely sure all copper is removed on a regular basis until it stops showing up. The only reliable way to know that all the copper fouling is gone before another firing is by using a borescope.
Voodoo, would it be time for you to share with us what your friends at the range came up with on your original question?
Tozguy: My sampling of muzzle coppering was minimal as I said with only 2 or 3 out of many barrel replacements over the past 10 years, but, the majority of copper was on the tops of all lands, grooves mostly clean. One of those barrels still will get very tiny fine lines of copper in the corners where the lands meet the grooves, and is very difficult to remove entirely, has not effected the excellent results I get with that barrel ( a 6BR 1-8 with 325 rds. fired) so other than keeping it under control I'm not concerned.
Not making a conclusion either way guys but will add a few observations and some more possibilities. From initial observations the latest 6.5mm barrel I installed coppers badly in the grooves (not on top of rifling) for the last 1/2 to 1 inch. BUT this observation is made after some cleaning. It may well have been badly coppered on top of rifling too but that might clean off more easily (see below). To be honest I havn't scoped a barrel before cleaning to see the difference.
It took a 4 ten thousands tighter reamer bushing at muzzle than chamber after trimming 3/4 inch off muzzle end
Indeed I believe when barrel manufacturers lap the bore they do not lap the ends as much (lap doesn't exit). They recommend when finishing a barrel to remove some of muzzle to get rid of this - I may have not removed enough but it shoots very well so am not going to worry.
Comment on cleaning. I also believe a lot of cleaning techniques do not "work" the last 1 inch of barrel as much as elsewhere. I watch a lot of techniques at the range and quite a few people will clean the bulk of carbon etc straight out end of muzzle then when it gets clean they follow the instructions on sweets bottle and scrub back and forward for a minute or so with 7.62 solvent or similar. This copper removing patch works heavily over barrel midlength but doesn't scrub the last inch or two anywhere near as much (if they don't exit the muzzle). Similar to the way the barrel manufacturers lap the bores.
It took a 4 ten thousands tighter reamer bushing at muzzle than chamber after trimming 3/4 inch off muzzle end
Indeed I believe when barrel manufacturers lap the bore they do not lap the ends as much (lap doesn't exit). They recommend when finishing a barrel to remove some of muzzle to get rid of this - I may have not removed enough but it shoots very well so am not going to worry.
Comment on cleaning. I also believe a lot of cleaning techniques do not "work" the last 1 inch of barrel as much as elsewhere. I watch a lot of techniques at the range and quite a few people will clean the bulk of carbon etc straight out end of muzzle then when it gets clean they follow the instructions on sweets bottle and scrub back and forward for a minute or so with 7.62 solvent or similar. This copper removing patch works heavily over barrel midlength but doesn't scrub the last inch or two anywhere near as much (if they don't exit the muzzle). Similar to the way the barrel manufacturers lap the bores.
The concensus was more along the lines of a "friction" related issue laying down more copper at the muzzle. But thanks to all of you for sharing your thoughts and understanding of this phenomenon.
Camac's cleaning observation seems like the missing link to tie some other observations together in support of the 'friction' theory.
If friction is highest in a new barrel, if firing/cleaning cycles eventually (maybe never in some production barrels) wear in the bore, reduce friction and consequently fouling, if one's cleaning technique means less cleaning at the muzzle, it seems reasonable to think that copper fouling, that may have been 'everywhere' to begin with, will take longer to diminish/disappear at the muzzle.
If friction is highest in a new barrel, if firing/cleaning cycles eventually (maybe never in some production barrels) wear in the bore, reduce friction and consequently fouling, if one's cleaning technique means less cleaning at the muzzle, it seems reasonable to think that copper fouling, that may have been 'everywhere' to begin with, will take longer to diminish/disappear at the muzzle.
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