  We investigate magnetotransport across an interface between two Weyl
semimetals whose Weyl nodes project onto different interface momenta. Such an
interface generically hosts Fermi arcs that connect Weyl nodes of identical
chirality in different Weyl semimetals (homochiral connectivity) -- in contrast
to surface Fermi arcs that connect opposite-chirality Weyl nodes within the
same Weyl semimetal (heterochiral connectivity). We show that electron
transport along the arcs with homochiral connectivity, in the presence of a
longitudinal magnetic field, leads to a universal longitudinal
magnetoconductance of $e^2/h$ per magnetic flux quantum. Furthermore, a weak
tunnel coupling can result in a close encounter of two homochiral-connectivity
Fermi arcs, enabling magnetic breakdown. Above the breakdown field the
interface Fermi arc connectivity is effectively heterochiral, leading to a
saturation of the conductance.
