80/20 silver as silver solder

For an extra hard solder for sterling silver, would it be possible to use an alloy of 80% silver and 20% copper or would the melting point be too high without any zinc. Would I be better off by alloying with “cartridge brass” rather than copper to get 80% silver, 14% copper and 6% zinc? I want a silver solder with as high a melting temperature as possible to get the strongest joints possible. I would like to avoid zinc for another reason, as it would make recycling without solder contamination easy, as there is only silver and copper involved. Just a few extra grains of fine silver to account for the lower silver content and I should be good. Thanks for any opinions on this,

ArgentumMoon