  The weak field magnetoresistance has seen a revived interest due to the
distinct role played by the momentum-space Berry curvature of Bloch electrons.
While most previous studies in this regard focus on the inter-scattering motion
of semiclassical Bloch electrons in electromagnetic fields, the
intra-scattering effects of the semiclassical dynamics augmented by the Berry
curvature, magnetic moment and shift vector on the magnetoresistance have been
largely overlooked. Here we uncover that these intra-scattering effects, which
are neglected in the field-independent relaxation time approximation to the
Boltzmann collision integral, can be as important as the inter-scattering ones.
Concrete calculations on the two dimensional gapped Dirac model show that the
sign of the negative linear magnetoresistance given by the Berry curvature
alone is reversed when one considers the magnetic moment and shift vector.
