I concur with SDC.
It looks like a Model 1905 FN/Browning mag, but it could be for any one of probably close to a hundred different .25s made in Spain prior to 1939.
FN/Browning mags usually (but NOT always) have the FN trademark logo on the side of the mag near the bottom end.
My second guess, since it looks to be fairly well made, would be an Astra 200, aka (in later years) as "Firecat."