The role of crystallographic grain size and microstructure of an austenitic stainless steel (A316LN) is studied via in-situ mechanical testing in an SEM and digital image correlation to measure displacement and strain fields. The latter ones are directly measured on a mesh supported by the grain boundaries as imaged by EBSD. This experimental analysis is applied to five microstructures of the same cast material but subjected to different heat treatments. Differences in the strain distributions that can be attributed to the grain size are observed. The full-field measurements allow in turn for a direct, local and quantitative comparison with crystal plasticity finite element simulations of the same experiments based on the same mesh. A weak correlation between the plastic strain and the Schmid's factors, which are computed with macroscopic or even local stress evaluations, emphasizes the role of inter-grain strain incompatibilities or grain boundaries. However, a good agreement in the major slip system evaluation between experimental observation and computations is observed.