What does "bi-metal" mean in relation to some 7.62x39 ammo? I think I saw this in a Wolf Ammo description.

Quoted: What does "bi-metal" mean in relation to some 7.62x39 ammo? I think I saw this in a Wolf Ammo description.

Steel case, steel bullet jacket, copper wash on the jacket, lead core.

Bi is from the Latin which means two.
Bi-metal means composed of two different metals.
With 7.62x39mm ammo it can be used to refer to the bullets or the case. As the bi-metal bullets are a mild steel jacket that is copper plated. This is done for three reasons cost,corrosion resistance,and to reduce friction. Steel is 8-1/2 cents per pound and copper is $1.78 per pound. So a steel jacket is 21 times cheaper than a copper jacket. Besides 1 Pound of copper can plate 10,000's of steel bullet jackets. The copper plating keeps the steel bullet jacket from rusting. Rust is made up of iron oxide which is a pretty hard substance so it wouldn't take too awful many rusty bullets to wear a barrel out. Copper being way softer than steel, the copper plating is what contacts the bore of the rifle not the steel jacket. So it creates less friction as the bullet is propelled down the rifle's barrel at high speeds.
Bi-metal can also refer to a steel 7.62x39mm case that is plated with another metal. The Russians used copper to plate all cases until they developed the technolgy to use lacquer on cases in the early 1960's and China plated all steel cases with copper till the early 1970's.
Now current imported Russian ammo under the Golden Bear brand has a bi-metal case that is steel plated with brass and the Silver Bear brand has steel cases plated with zinc or nickel.