  We examine the exchange of angular momentum between the component spins and
the orbit in semi-detached double white dwarf binaries undergoing mass transfer
through direct impact of the transfer stream. We approximate the stream as a
series of discrete massive particles ejected in the ballistic limit at the
inner Lagrangian point of the donor toward the accretor. This work improves
upon similar earlier studies in a number of ways. First, we self-consistently
calculate the total angular momentum of the orbit at all times. This includes
changes in the orbital angular momentum during the ballistic trajectory of the
ejected mass, as well as changes during the ejection/accretion due to the
radial component of the particle's velocity. Second, we calculate the
particle's ballistic trajectory for each system, which allows us to determine
the precise position and velocity of the particle upon accretion. We can then
include specific information about the radius of the accretor as well as the
angle of impact. Finally, we ensure that the total angular momentum is
conserved, which requires the donor star spin to vary self-consistently. We
calculate the angular momentum change of the orbit and each binary component
across the entire parameter space of direct impact double white dwarf binaries.
We find a significant decrease in the amount of angular momentum removed from
the orbit during mass transfer, as well as cases where this process increases
the angular momentum of the orbit at the expense of the spin angular momentum
of the donor. We conclude that, unlike earlier claims in the literature, mass
transfer through direct impact need not destabilize the binary and that the
quantity and sign of the orbital angular momentum transfer depends on the
binary properties. This stabilization may significantly impact the population
synthesis calculations of double white dwarf progenitors.
