  In the hadroproduction of charm (or heavy flavours in general) in the context
of string fragmentation, the pull of a beam remnant at the other end of a
string may give a charm hadron more energy than the perturbatively produced
one. The collapse of a low-mass string to a single hadron is the extreme case
in this direction, and gives rise to asymmetries between leading and
non-leading charm hadrons. We study these phenomena within the Lund string
fragmentation model and improve the modelling in part by a consideration of
hadroproduction data. Applications include heavy quark production in any
collision between hadron-like particles such as \gamma p at HERA and pp at
HERA-B or the LHC.
