"John McCorkle that states on page 154:

We took a number of the pistols that the enemy were using which were a very large caliber pistol"
Kind of sounds like it might have been the caliber you are describing. It would indeed be a large caliber. I did find some of what were described as French Dragoons but they looked more like they belonged to the late 1700's than the middle 1800's. Flint locks and not modern at all. FC