If you are experiencing problems with breaking strings then this article may help isolate some issues.
”Strings do break from age or because of a flaw in the string but most string breakages are caused by a problem with the instrument…”
Martin FX MFX650 Bronze 13-56 MEDIUM
Martin FX Flexible Core acoustic guitar strings have a thinner core wire with zinc flashing. This delivers greater player control with sharp attack, increased flexibility and improved harmonic sustain.
Martin 80/20 Bronze is an alloy comprised of 80% copper and 20% zinc. 80/20 bronze strings provide a very brilliant tone when they are initially put on the guitar and mellow over time.