We have used ultra-small-angle neutron scattering (USANS) with contrast variation to measure the porosity over length scales 0.1 - 20 mu m in a composite high explosive, PBX 9501, formulated with a deuterated binder. Here, we explore the effect of varying the pressing intensity on the PBX 9501 microstructure. Samples of PBX 9501 were die-pressed with applied pressures ranging between 69 and 200 MPa at 90 degrees C. Five samples were prepared at each pressure that differed in the fraction of binder that was deuterated, resulting in a change in the neutron scattering length density contrast (Delta rho) of the binder relative to that of the high explosive crystallites and voids. By using this approach to discriminate scattering from voids from that clue to the binder, we determined microstructure and composition that otherwise would not have been apparent. The sample composition was determined by calculating the Porod Invariant as a function of Delta rho and comparing it with compositional estimates obtained from the bulk sample density. Structural modeling of the USANS data, assuming both spherical and cylindrical morphologies, allowed the mean size and size distribution of voids and binder-filled regions to be determined.