A recently developed reconstruction technique titled nozzle-throat reconstruction technique is used to investigate graphite nozzle-throat-erosion in two scales of hybrid rocket motors, 30N-thrust class and 2000N-thrust class, using oxygen as the oxidizer and high density polyethylene as the fuel. Thirty seven static firing tests were conducted under varying experimental conditions to confirm the validity of the reconstruction technique results, investigate the conditions at the onset of erosion and to formulate an empirical predictive model of nozzle erosion rate. Results show that nozzle erosion increases the convective heat transfer coefficient to upwards of 2-4 times the value predicted by Bartz correlation. Furthermore, an empirical model is introduced that treats the combustion gas as a single oxidizing agent with heterogeneous rate constants that are distributions of equivalence ratio of the bulk fluid flow. This empirical model predicts the nozzle throat erosion histories in multiple tests to within ± 5%.