The self-interaction force of dislocation curves in metals depends on the local arrangement of the atoms and on the nonlocal interaction between dislocation curve segments. While these nonlocal segment-segment interactions can be accurately described by linear elasticity when the segments are further apart than the atomic scale of size ε, this model breaks down and blows up when the segments are O(ε) apart. To separate the nonlocal interactions from the local contribution, various models depending on ε have been constructed to account for the nonlocal term. However, there are no quantitative comparisons available between these models. This paper makes such comparisons possible by expanding the self-interaction force in these models in ε beyond the O(1)-term. Our derivation of these expansions relies on asymptotic analysis. The practical use of these expansions is demonstrated by developing numerical schemes for them, and by -for the first time -bounding the corresponding discretization error.