The largest copper coin struck within the last 100 years that I can think of right now is a Chinese coin. Issued around 1928 in Honan Province, it weighs around 30 grams and diameter of 40.6mm. Mine is a low grade, weighing at 28.9g. I should have a better one somewhere

Here's a link
http://en.numista.com/catalogue/pieces26402.htmlI reckon it would be hard to top that coin. The Kweichow 1949 1/2 cent coin comes pale in comparison at 17.5g.
A slightly lighter coin but bigger would be the Szechuan 1913 200 cash (guess it's slightly over 100 years old). Diameter at 42.6mm and weighs around 24g. I would like to get it one day - it's not particularly rare I believe.
http://en.numista.com/catalogue/pieces27897.htmlWould like to see if there are any copper coins bigger than these without going over the 100 year limit.