Gary,

My guess is that Model Nº51 was mostly exported to Iberian countries where pigeon shooting was more common and money was less abundant. By the seventies Belgian and Italian over/unders were removing the Spanish side-by-sides from the clay and pigeon grounds in most Southern countries in Europe and the Americas. I use my Nº51 mostly on feral pigeons and goes many more times to the field than my bespoke Nº53.

Regards.

EJSXS