A new process for continuous manufacturing of composite propellants has been developed using Twin Screw Extrusion (TSE). The effects of TSE-processing on the burning rates of an ammonium perchlorate (AP)-based composite propellant have been characterized over a wide composition range (79 to 87 wt. % AP) and a wide range of screw speeds (45 to 85 RPM) using a quadratic model for an experimental Response Surface Analysis (RSA) based on the Kowalski, Cornell, and Vining (KCV) algorithm. Using Student's T-test, it was determined that burning rates obtained from strand-burning rate tests at 3.5 MPa, 7.0 MPa, and 10.5 MPa are affected only by the individual ingredients, the interaction between the coarse AP particles and the binder, and the screw speed. Measured burning rates were found to be 40% to 100% higher than Petite Ensemble Model (PEM) predictions, which was accounted for by modifying the PEM through a power law relationship with pressure that includes a rule-of-mixtures dependence of the exponent and coefficient on the weight fraction of coarse and fine AP particles. The resulting modified PEM reduced differences between the predictions and experimental data by 79% at 3.5 MPa, 83% at 7.0 MPa, and 78% at 10.5 MPa.