Beam simulation has been used to estimate scattering from large surfaces by calculating the scattering from the individual subsurfaces and then summing over these subsurfaces. Previously physical intuition and comparison to method of moments (MoM) calculations were used to determine beam simulation's region of validity. Here the MoM operator is used for a direct comparison of beam simulation to MoM. The improved speed of comparison allows a more in-depth analysis of beam simulation at a lower computational resource cost. Scattering from one-dimensional random surfaces with Gaussian height distributions will be specifically examined to verify and clarify earlier beam simulation validations. Although one-dimensional surfaces are an oversimplification for most applications, they are well studied and are likely to give insight into higher dimensional applications.