Copper shell

[fortierdan]

I've recently started collecting different cartridges, and I got a whole slew of the from my father. While going through them all, I've come across a 12 gauge shotgun shell that appears to be made of copper. It's got 12 for the gauge, and the number 92 stamped on the bottom along with a small symbol that is a square separated in half with a notch in the middle. (Sorry, my camera is broken right now otherwise I'd have a picture to go along with this.) There is also a clear plastic plug in the top covering a piece of paper with the letter Z on it (Possibly a 2).

Can anyone tell me anything at all about this? Where it may of come from, when it could of been made? Anything at all?

 

[sunray]

Copper was used before brass. However, it's possible that your cases is brass with the copper coming out.
"...clear plastic plug..." Indicates a post-W.W. II case.
"...12 for the gauge, and the number 92..." Might be Pretoria Metal Pressing Ltd Pretoria, RSA or O.J.F. (Osterreichische Jegdpatronenfabrik) Kremsach(Austria, I think).
"Z" is used by Zbrojovka Brno, Brno, Czechoslovakia on head stamps.
I'd bet the square is the key though.