American barrel making began in the late 1600's or very early 1700's, with many gunsmiths making muskets and fusils, while German immigrant gunsmiths started making rifles in the 1720's. (perhaps earlier, though extant records can not verify this..) Remington began as a rifle barrel making concern in 1816, when founder Eliphalet Remmington made his first rifle, using a purchased lock, but making the rest himself.
I am inclined to believe that the auction house was probably right in their estimate. 1840 to maybe 1860, but more probably earlier than later, based on the comparatively small caliber.