Dissimilar metal weld (DMW) joints are widely used in nuclear power plants to connect ferritic steel components with austenitic steel piping systems. AREVA has designed a new narrow gap DMW with nickel-based corrosion resistant weld filler (Alloy 52) to reduce the risk of stress corrosion degradation. Engin-X neutron measurements of the stress-free lattice parameter in small samples removed from a DMW mock-up supplied by AREVA have exhibited wide scatter between different orientations (up to 600 micro-strains). The OU is undertaking research examining the origins of uncertainty in stress-free reference measurements in DMW materials. The purpose of the present experiment is to investigate random errors, beam divergence, spatial variability and systematic rotational effects in d-spacing measurements of stress-free reference samples extracted from the AREVA DMW mock up.