The Jaeger rifle, per se, began as wheel lock versions in the 16th century but probably converted to flint ignition late in the 17th. The first known rifle makers of German extraction who specialized in the type seem to have arrived in North America around 1710...give or take a decade. Most quickly gravitated to longer barrels with smaller bores fairly quickly. As to when they would have been in use here I'd have to make a WAG of about 1730ish. Rifles of the type were sent during the various wars against the French during the 1750-1763 period and German (usually called Hessian) Jaegers were active during the AWI era as well. Original pieces generally had much slower rifling than Pedersoli's modern copy but a fast twist doesn't prevent it's use with patched round ball, just keep powder loads moderate.