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Bi-Metallic Corrosion?

This has been a difficult topic for me to find anything on....

Lets see if I have this correct, Copper & Lead are "Noble" metals....or very close to them, so how can they react with steel, causing corrosion if left in a rifle barrel on a long-term basis?

Anyone have any ideas on this?

Curious......

'toes
 
Brass is made up with copper and zinc. It's the zinc that's an issue. Boats use sacrificial anodes made of zinc so that the zinc gets eaten away not the more expensive running gear...
 
Hi,
I work as a plumber and roofer and we see this all the time.
Basically copper and brass will make steel corrode.
Aluminium will make steel corrode.
Moisture and specialy saline moisture helps a lot in that chemical reaction.
Nd
 
aj300mag said:
Google Dissimilar Metal Corrosion... ;)
+1. And Remember a truism a former boss of mine told me: "The whole world is a battery waiting to happen." Anytime you work with dissimilar metals you have the possibility of an electrical potential and electrolytic corrosion. One I worked with for years was KMonel fasteners threaded into steel - the electrical potential of that matchup is on the order of 0.7 volts....
 
Some of it makes sense to me.....yea, I've been a plumber too. I understand Galvanic reaction, and how it would differ from Bi-metallic reaction. Yes I understand that some of the "least" noble metals are zinc and magnesium......yet the only brass used in my firearms is the case, and it does not go down the barrel, nor does it leave anything in the barrel. The only brass bullets I've heard of are used in 50 cal or larger. I've never used anything except copper jacketed bullets witch I'm sure are low in impurities. Yes we fire gun powder down the barrel, but other than graphite and nitro-cellulose (and other chemicals-and this depends upon single or double-based powder), I still don't see the correlation.
I understand anodes corrode, cathodes do not...and in a moist enviroment, the barrel steel could possibly become the anode....? Not sure on this one. Dissimilar metals do react with each other, but with two of them being copper and lead.....low on the "corrosion" scale....it's difficult for me to just "except" without a better explanation.
I HAVE seen copper-jacketed lead bullets "expand" (it was the lead expanding!), and THIS confuses me too! Of course! ;)

Lead expands with time??? Anyone else seen this??? Found an old loaded round in the woods, and the lead tip has out grown the copper jacket??? What is with this, and how do you explain it???

And what is the "white" oxide that forms around the lead? Yep, I nailed it-"Oxide", but that's still not a true answer....."Lead-Oxide"? Is that even an answer??? I HAVE seen the same material in rifle barrels that folks didn't clean often enough.....I have one friend that stores his rifles behind his wood stove in his shop.....frightful-scary to me. Worse possible place you could store a rifle if you ask me, other than the family chlorine pool...
 
littletoes said:

Well, this is not theoretical, cuz when I took chemistry, the professors were still trying to turn lead into gold...

... but from a practical point.

A long time ago, I needed to move my 18 tons of loading junk, and 90+ firearms very fast (an angry divorce in the works).

So I quietly found new digs with a decent basement/work shop area and my friends and I did a frantic 2 day weekend "move". Everything was put in the basement and left there while I moved in furniture, etc, etc, etc.

A longtime later, I got to hanging up rifles on the wall, and opened the case to a quality, 30 calibre, 1,000 yard match rifle. It had not been cleaned in the panic :(

There was a white fuzz all through the bore of the stainless barrel - I don't mean something light - I mean the bore was full, all the down the barrel, like what you see on the yogurt you left in your desk drawer from last summer :( :( :(

I'll skip the description of the rants, screaming, tears, self guilt, and emotional pain (and visions of a new $$$$ barrel)... I put a chamber plug in it, filled the bore with Hoppe's #9, and let sit with the barrel up for four days.

When I ran the first patch through it, sludge came out... then I did a normal cleaning. When the barrel was checked with a bore scope, there was absolutely no sign of anything - nothing at all.

There was no damage - the fur was a tin/copper interaction with normal moisture, aided with the chemicals left behind from burnt powder and primer residue.

So, that is what happens in reality.
 
littletoes said:
...Copper & Lead are "Noble" metals....or very close to them, so how can they react with steel, causing corrosion if left in a rifle barrel on a long-term basis?

Dissimilar metals have an electron exchange potential which varies according to their atomic structure. The Noble metals merely denote metallic elements that resist corrosion in moist air. In a rifle barrel there's more going on because of the presence of other elements (iron, chromium, molybdenum, sulfur, carbon) which make up the barrel's metal matrix, along with leftover stuff from the passage of bullets and combustion of propellants and priming compounds.

Mercuric primers used to cause dramatic corrosion because of the (relatively) high reactivity of mercury and it's compounds in the presence of air. With lead-based priming compounds the potential is greatly diminished but it's still there, make no mistake.

So-called stainless steels can still rust under the right (wrong?) conditions. Some stainless alloys are worse than others in this respect.

Bottom line is you want to eliminate the leftovers as much as possible while also preventing water vapor and oxygen from reaching what's left, including your bores. That's why a light coating of a good gun oil is a good idea once you've cleaned a bore.

I myself use ATF fluid, mostly because I bought a quart for breaking bores in (PM me please if you want to discuss this) so I have a lot on hand that otherwise would go to waste. My car's a manual shifter, just like my bolt guns....
 
I've used Kroil for years, clean with it mixed in with Shooter's Choice too. I definitely think it makes later cleanings much easier.

Mercuric primers produced salt when fired, and isn't it the chromium content in stainless that prevents the rust, but produces a steel that is too soft? Too soft for barrel steel, I think.

CatShooter-That is real interesting! I've seen "white" powder like substance, but never a barrel completely fuzzy.

But why does lead expand with age??? I've got an old bullet somewhere around here.....need to take a pic.
 
littletoes said:
I've used Kroil for years, clean with it mixed in with Shooter's Choice too. I definitely think it makes later cleanings much easier.

Mercuric primers produced salt when fired, and isn't it the chromium content in stainless that prevents the rust, but produces a steel that is too soft? Too soft for barrel steel, I think.

CatShooter-That is real interesting! I've seen "white" powder like substance, but never a barrel completely fuzzy.

But why does lead expand with age??? I've got an old bullet somewhere around here.....need to take a pic.

Your second paragraph should bring some serious responses.
 
littletoes said:
I've used Kroil for years, clean with it mixed in with Shooter's Choice too. I definitely think it makes later cleanings much easier.

Mercuric primers produced salt when fired, and isn't it the chromium content in stainless that prevents the rust, but produces a steel that is too soft? Too soft for barrel steel, I think.

CatShooter-That is real interesting! I've seen "white" powder like substance, but never a barrel completely fuzzy.

But why does lead expand with age??? I've got an old bullet somewhere around here.....need to take a pic.

Mercury primers didn't contain or make salts.

Mercury Fulminate is an organometalic explosive - Hg(CNO)2 - when it explodes it leaves carbon dioxide, nitrogen, and metallic Mercury vapor. The waste was metallic Mercury vapor. It didn't attack the barrels, it attacked the brass case, making them brittle and unusable for reloading.

It was the chlorate primers that attacked the (plain) steel barrels and rusted them in no time.
 
dkhunt14 said:
Nosler partitions used to be brass. I think I saw Remington bullets in brass.

All "copper" bullets are a mild brass called guilding metal - 95% copper, and 5% zinc.
 

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