Feeding and handling problems have been recognized as a major contributor to low production of renewable cellulosic ethanol in the US, which achieved only 7% of nameplate capacity in 2016. In this work we compare the flow behavior of pine forest residues and corn stover at various particle sizes and moisture contents in instrumented pilot-scale hopper tests and instrumented shear testers to continuum finite element method (FEM) and discrete element method (DEM) models. The shear testers include a Schulze ring shear tester, a custom large Peschl-style tester, and a modified Johanson direct shear tester. In addition to measurements of normal force and torque, the shear testers are also instrumented with arrays of pressure transducers. Modeling approaches include a Drucker-Prager model, a micropolar hypoelasticity model, and DEM simulations employing non-spherical, deformable particles. Results from physical experiments indicate that continuum elastoplastic models, such as Drucker-Prager models, do not account for the full complexity of biomass flow, and that more advanced rheological models are better able to predict nuances of the flow behavior, especially the compressive stress field.