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Does anyone know why there is always more copper fouling on the tops of the lands than there is in the grooves?
Lots of statements made tonight and many open up topics we should have been talking about for the last 15 years.
This isn't school and I do know the answer but lets talk about it.
 

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After the shot Is a cup and core bullet perfectly round with nice little slices where the lands hit or is it kind of deformed and square with round corners, why?
 

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Ok, here's my lay person thought on the topic.

Where the lands engrave into the bullet, there is more friction/heat and direct contact of copper/steel. The steel being harder, any machining marks on the steel peel off the softer/hot copper and hold it in those machining marks.

Where the grooves/bullet contact, the air inside the barrel is being channeled into and compressed between steel on three sides and copper on one side. At the same time, hot/burning gases are heating/deforming the base of the bullet to form a seal to keep things moving forward. I'd imagine there are some interesting things happening in those grooves near the ogive. Things probably get a little malleable/fluid in there.

Depending upon the diameter of a given projectile, and the hardness of the copper, some of those hot gasses may escape between the bullet/lands (prior to the seal) and may erode/burn off or have an effect on the resulting deformation of the projectile.

Beyond those thoughts, I must claim ignorance.
 

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Lots of statements made tonight and many open up topics we should have been talking about for the last 15 years.
And that's the way it should be. And should stay.
'Politics' happens everywhere but FACTS result in knowledge.
 

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Discussion Starter · #5 ·
Ok, here's my lay person thought on the topic.

Where the lands engrave into the bullet, there is more friction/heat and direct contact of copper/steel. The steel being harder, any machining marks on the steel peel off the softer/hot copper and hold it in those machining marks.

Where the grooves/bullet contact, the air inside the barrel is being channeled into and compressed between steel on three sides and copper on one side. At the same time, hot/burning gases are heating/deforming the base of the bullet to form a seal to keep things moving forward. I'd imagine there are some interesting things happening in those grooves near the ogive. Things probably get a little malleable/fluid in there.

Depending upon the diameter of a given projectile, and the hardness of the copper, some of those hot gasses may escape between the bullet/lands (prior to the seal) and may erode/burn off or have an effect on the resulting deformation of the projectile.

Beyond those thoughts, I must claim ignorance.
Agree 100%. Copper fouling is due to pressure from the .0035" tall lands engraving the bullet.

Remember years ago when we use to talk about making sure all of the copper was cleaned out of the bore before shooting Barnes bullets? Those bullets just didn't like a different kind of copper in the bore.
 

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After the shot Is a cup and core bullet perfectly round with nice little slices where the lands hit or is it kind of deformed and square with round corners, why?
Not sure if the following is what your question was about, but it seems informative regardless.

In this link there is a good photo of a couple recovered Barnes bullets. It looks as though the bullet is deformed by the lands and metal is displaced into the groove.


In this link there are some pretty good photos of recovered cup and core bullets. From the photos it looks like the lands displace material into the softer core instead of pushing it out into the grooves.

 

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Agree 100%. Copper fouling is due to pressure from the .0035" tall lands engraving the bullet.

Remember years ago when we use to talk about making sure all of the copper was cleaned out of the bore before shooting Barnes bullets? Those bullets just didn't like a different kind of copper in the bore.
I always found it necessary to de-copper the bore before switching to jacketed bullets in order to obtain the best grouping.
 

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I always found it necessary to de-copper the bore before switching to jacketed bullets in order to obtain the best grouping.
This is due to all the different types of copper used in both monolithics and copper jacket material. There are 5 types of copper used in bullet jackets that I know of.
Just like there are different hardness ratings in lead there are in copper also. As well as compositions.
C100, C105, C110, C114 etc. Also where the copper comes from matters. German copper is different than Mexican copper for example. The ore is different so it produces a different structure in the metal. All copper is not created equal.
With CBB we are picky about where our copper comes from. To keep consistent performance
 

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I know different jacket / bullet material may need to be cleaned before experiencing good groups with a different bullet and I'm definitely not arguing that it shouldn't . But don't just assume you need to clean between jacket types or even bullet types without testing . For instance , I have shot 120 SST - S&B- Federal Fusion - TNT - and Cavity Back Bullets all through my wife's 16" ARP barrel since initial cleaning and none were bad and most were great groups . That was before she told me I had plenty of guns to play with and to put her scope back on hers and sight it back in with her bullets . So I did just that and sighted it in at 200 yards with 120 SST s . Even though it hadn't been cleaned I shot the best 2 - 5 shot groups I have ever shot with a carbine . I would clean it and sight it in with Cavity Back Bullets but if it ain't broken don't fix it . And my marriage isn't broken so I ain't playing with her gun again until it breaks .

Sent from my LM-K920 using Tapatalk
 

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I know different jacket / bullet material may need to be cleaned before experiencing good groups with a different bullet and I'm definitely not arguing that it shouldn't . But don't just assume you need to clean between jacket types or even bullet types without testing . For instance , I have shot 120 SST - S&B- Federal Fusion - TNT - and Cavity Back Bullets all through my wife's 16" ARP barrel since initial cleaning and none were bad and most were great groups . That was before she told me I had plenty of guns to play with and to put her scope back on hers and sight it back in with her bullets . So I did just that and sighted it in at 200 yards with 120 SST s . Even though it hadn't been cleaned I shot the best 2 - 5 shot groups I have ever shot with a carbine . I would clean it and sight it in with Cavity Back Bullets but if it ain't broken don't fix it . And my marriage isn't broken so I ain't playing with her gun again until it breaks .

Sent from my LM-K920 using Tapatalk
I don't clean between jacket types usually either. Although I have have it thighten up groups with certain cup core bullets. I was sharing that stuff because I think a lot of people think copper is copper. If they are not getting the accuracy they think they should it's something to look at though. Sounds like you've got that figured out :)
 

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I have read a couple of times that switching bullets could have a temporary effect of accuracy for the reason that Yamaraja stated. The recommendation was to shoot a few of the new bullets to "season" the barrel prior to shooting for accuracy. I forget if the recommendation was five or ten rounds.

FWIW, I once worked at a factory that made pneumatic valves and used large quantities of several different types of brass ("copper alloys" as the spec sheets called them). Each batch contained a chemical analysis of its composition. It amazed me that even very small variations in composition could change properties enough to give us problems. Sometimes a particular alloy could still be technically "in spec" and not work well for us. Luckily we were a large enough customer that the mills would usually send us select batches of material that worked best for us (towards the high or low end of certain of particular elements). When they didn't, we would have to change our machining, plating, or rubber molding processes for that batch.
 
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