His corps, the relics of his father Rob's band, behaved with great activity; with only twelve men he succeeded in surprising and burning, for the second time, the fort at Inversnaid, constructed for the express purpose of bridling the country of the MacGregors.
What rank or command James MacGregor had, is uncertain.

He calls himself Major; and Chevalier Johnstone calls him Captain.

He must have held rank under Ghlune Dhu, his kinsman, but his active and audacious character placed him above the rest of his brethren.

Many of his followers were unarmed; he supplied the want of guns and swords with scythe-blades set straight upon their handles.
At the battle of Prestonpans, James Roy distinguished himself.

"His company," says Chevalier Johnstone, "did great execution with their scythes." They cut the legs of the horses in two--the riders through the middle of their bodies.