Hi,
1937 - 1942 .955 copper, .030 tin, .015 zinc - weight 3.24 grams
1942 - 1979 .980 copper, .005 tin, .015 zinc - weight 3.24 grams
1980 - 1981 .980 copper, .005 tin, .015 zinc - weight 2.80 grams
1982 - 1996 .980 copper, .005 tin, .015 zinc - weight 2.50 grams
1997 to date copper-plated zinc - weight - 2.25 grams
And you thought it would be easy :-)
Have Fun,
Bill