[JimRed]

This was the weakest part of the stock as it had been drilled & inletted as well. Breakages were common.

When the fighting went hand-to-hand and they used it as a club?

[elcid1970]

Likely just ordinary wear & tear, in & out of saddle scabbards, etc.

A clubbed musket is a formidable arm; the lightweight Henry not so much.