7.62x39 cases- copper clad, copper plated copper washed


#1

Today i was given a 10 rd. stripper clip of 7.62x39’s clip has a 31 in a circle. cartridge headstamp of 31 over a 65, copper washed with a black extractor grove. why the black extractor grove?


#2

Because the case was drawn from a copper plated steel strip and the extractor groove was machined after drawing and had to get a corrosion protection since the bare steel got exposed there.

Your cartridges are Chinese.


#3

The case was drawn from a copper-clad steel cup. When the extractor groove was cut, it exposed bare steel, so lacquer was applied to prevent rust.

This is typical for this caliber and case material. A notable exception is North Korean 7.62x39mm which have the entire steel case copper plated after the extractor groove is cut. Early Soviet and Chinese steel cases that were brass plated also appear to have been done after the extractor groove was cut, but why this was not done the same way with copper is unknown to me. Perhaps using copper-clad steel was easier on the tooling compared to bare steel.

AKMS


#4

EOD, we need to clarify the definitions of “copper-plated” and “copper-clad”. They seem to be used interchangeably but are two totally different things…

I beleive in this case, “copper plated” is incorrect.

AKMS


#5

AKMS–Here is the note I have added to the listing of case materials:

NOTE


#6

[quote=“AKMS”]EOD, we need to clarify the definitions of “copper-plated” and “copper-clad”. They seem to be used interchangeably but are two totally different things…

I beleive in this case, “copper plated” is incorrect.

AKMS[/quote]

AKMS, what would be copper-clad in your view?


#7

Just to jump into the mix…From what I recall:

Ron’s above description of “Bimetallic Copper Plated Steel” is generally called “cladding”. Mechanical and thermal applications of energy are used in the process. Electroplating copper onto the steel is also called “copper washing” and is an electro-chemical process. I have seen “plating” used to generically describe both processes. I would guess the mechanical process would be a more efficient way of getting copper on your steel in the volumes involved with ammunition manufacture.

As an interesting application of clad materials, U.S. coinage in .10, .25, .50 and $1.00 denominations are made from a pure copper core and copper-nickel outer layers (other materials for the $1.00) . The interesting part is the process used very successfully is “explosive cladding” (or “explosive forming”) where huge sheets are laid out and a precision layer of AN-FO is detonated on top of it. Now that’s probably a fun job…

Dave


#8

EOD,

DaveE. pretty much summed it up. Cladding is the mechanical application of copper to another metal (steel), usually done through rolling the two sheets together under pressure. Plating is an electrochemical process. “washing” is also known as “flashing” or “flash coating” in the plating trade and although uses the same process as plating, results in a much thinner coating, used where better adhesion is required for another type of metal. I.e., a steel automotive part might be copper “flashed” before being chrome plated. The copper sticks to the steel better and the chrome sticks to the copper better.

This information comes from my local plating shop.

So, as I see it, “bi-metal” = cladding, and “copper washed steel”, while technically incorrect, = copper plating.

To confuse the subject even more, I beleive the material used here in most cases is actually “gilding metal”, a copper alloy, and to be the most precise, copper clad steel cases and projectile jackets are actually “GMCS” - gilding metal clad steel.

AKMS


#9

Ok so there are just different names to the same procedures.

  1. galvanic applied copper = copper washed
  2. pressure heat type pressed on copper layer= copper plated

#10

No, you are misunderstanding. They are not the same. In fact they are quite different processes.

  1. Galvanic applied copper layer = copper plated.
  2. Pressure heat type pressed on copper layer = copper clad.

The end result is the same: you get a layer of copper applied to a base metal, usually steel, but how it is done is different.

Copper “wash” is a thin layer of copper plating, insufficient for wear or corrosion resistance.

AKMS


#11

AKMS, I am confused now.
How is the “washed” done if not galvanic?


#12

It is done galvanic, but for a shorter period of time. When a piece of steel is being electroplated, the longer it stays in the acid solution with a copper anode, the more copper molecules adhere to it.

“wash” = thin layer.

“plated” = thick layer.

The person I spoke with at the plating business was not able to give a specific point where a wash becomes plating.

AKMS


#13

OK I tossed these things at a magnet…any an every part stuck quickly…Took a knife and drug a ‘line’, and it looks shiney, cant tell if it turned ‘silver’ or not…


#14

That is becaue both the projectile jacket and case are steel, not to mention the core of the projectile is also steel.

AKMS