Samples were sealed inside 0.2 mm diameter borosilicate capillaries in an Ar-filled glovebox. 16-hour scans were conducted on a Bruker D8 Advance with monochromatic Cu Kα1 radiation (λ = 1.54056 Å) in Debye-Scherrer geometry to obtain high quality data for structural refinement. A LaB6 internal standard was ground into the CuBiSeCl2 mixture to extract accurate lattice parameters during refinement. 12 hour scans were conducted on an X'Pert Panalytical diffractometer with monochromatic Co Kα1 radiation (λ=1.788965 Å) in Bragg-Brentano geometry to quantify the extent of preferred orientation in pressed pellets of CuBiSeCl2. Rietveld refinements against CuBiSeCl2 PXRD data were conducted using TOPAS Academic V5. The background, lattice parameters, atomic positions, and atomic displacement parameters were refined against the data, a Chebyshev polynomial function was used to model the background, and the peak shapes were modelled using Stephens orthorhombic functions. Structural refinement parameters are available in the Supporting Information (S17).