Purpose: The goal of this work was to finalize the electron source parameters of a Varian 6 MV BEAMnrc model through the simulation of jaw collimated small fields. Methods and Materials: For nominal field sizes of 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 cm profile data was acquired in water using a stereotactic field diode (SFD) and EBT2 film. To achieve a positional error below ± 0.01 cm a stepper motor driven linear actuator device was incorporated into the Wellhofer water tank. At electron energies of 6.0, 6.1 and 6.2 MeV the spatial distribution of the electrons incident on the target was modelled as a Gaussian. The FWHM was decreased in steps of 0.010 cm from 0.150 to 0.100 cm. DOSXYZnrc simulations were run and profile data extracted for comparison. Results: The SFD and EBT2 profile data were found to be in good agreement with small differences believed to be the result of non‐uniformities inherent to the film. In all cases the measured field sizes were found to be smaller than the nominal and the simulated field sizes adjusted accordingly. At a FWHM = 0.150 cm the penumbral width was much too broad and the smallest field widths wider than experiment. As the FWHM was decreased from 0.150 to 0.110 cm the fit became progressively better, yet worsened at a FWHM = 0.100 cm for all but the smallest field size. Conclusion: Small jaw collimated fields can be used to fine tune the electron source parameters used in a BEAMnrc linac model.