The market is narrow: Lamy refills like the M30 or M32 fit with some adjustment but write only moderately well (the M30 is felt-tip-like, the M32 rated as critical). The M30 does not fit in the LeGrand. Workable alternatives from personal testing include the Schneider Topball 850 with a wider stroke and good writing behaviour — adjustment also needed here. In general the comfort of a fountain pen for heavy writing is regarded as superior to a rollerball, so this is a niche issue with limited supplier choice. Anyone wishing to experiment should test various gel and ink-roller refills as well as fibre refills, and possibly keep Montblanc's original refills for occasional premium use.