In linearised continuum elasticity, the elastic strain due to a straight dislocation line decays as O(r −1 ), where r denotes the distance to the defect core. It is shown in [7] that the core correction due to nonlinear and discrete (atomistic) effects decays like O(r −2 ).In the present work, we focus on screw dislocations under pure anti-plane shear kinematics. In this setting we demonstrate that an improved decay O(r −p ), p > 2, of the core correction is obtained when crystalline symmetries are fully exploited and possibly a simple and explicit correction of the continuum far-field prediction is made.This result is interesting in its own right as it demonstrates that, in some cases, continuum elasticity gives a much better prediction of the elastic field surrounding a dislocation than expected, and moreover has practical implications for atomistic simulation of dislocations cores, which we discuss as well.