Ben,
I have no difinitive word on the manufacture of this rifle, but it may be a pre-war target competition rifle utilizing a Remington base barrel. The information on the Pa man may be a gunsmith who manufactured the rifle or re-worked it, possibly changing the caliber or giving it a faster rate of twist, which would improve the accuracy. As far as the notion of being difficult to carry, a large target rifle like this which utilized weight to hold a steady aim would be caried in a wagon. I have read a biography on Patrick Clebourne that states his snipers/sharpshooters would carry a lighter regular musket on the march while their heavy precision arms were brought in the wagon train, and only manhandled for the short distance to the roost.