The weights of these coins are all over the place. They're supposed to be betwen 3,8g and 4,2g (see the uploaded pic), but the variation can be bigger. I weighted some of my coins and these are the results:
20c: 4,23, 4,08, 4,54, 4,04, 3,98
10c: 3,02, 2,92, 3,28, 3,36, 2,99, 2,97, 2,70, 3,03, 2,44, 3,11
Here's the law that rules about the weights of these coins:

Though there is an earlier decree (
https://www2.camara.leg.br/legin/fe...al-1-pe.html) that was supposed to be revoked, the weight variation would be in the window that it had set.