Gage sizes of silver and copper wire

If a wire is a certain gage is that size constant across different
types of metal?

I used my disc cutter with 22 gage sheet copper and 18 gage copper
wire to make discs and jump rings until I had a design that I liked
for a necklace.

I then attempted to make the same design with Argentium silver.

The Arg sheet behaved in ways similar to the copper.

When I went to make the jump rings, the 18 gage Arg silver seemed to
be not as robust.  I can lay the silver and copper side by side on the
table and feel that the copper is larger in diameter.

I know that the copper is stiffer, but it also was bigger.

Is this just a fluke?  Did I get mislabeled wire, or are they supposed
to be different?

I would not use 18 gage wire again to hold the washer shapes
together.  My design has redundency, 3 jump rings hold each pair of
discs.

I have tried to keep everything labeled and separate when I buy new
supplies. My  wire still has the original tag on it from the supplier.
This makes me think that I should get a wire and sheet gage.

Linda