D. João IV, 1641, Meio Tostão (50 Réis), prata, Cruz cantonada e cercada por pon

[Luis Cozeto]

Lisboa ,
D G REX.P
Diâmetro: 21,00 mm
Peso: 2,79 gr.
A.G.- 46.03

[Figleaf]

An interesting piece. Gomes says it should be 22 mm, 4.1 gram. At 2.79 gram, your coin is significantly (32%) underweight. Assuming that both you and Gomes got the weight right, the possibilities are a) underweight flan and b) clipped coin.

The argument for clipping is the straight (filed?) edges at 1-2 and 4-5 o'clock (top picture). The argument for thin flan (or end of batch) is the diameter, that suggests the coin is about the right size.

Peter