If the barrel says Lymans it is an old trade rifle as the new Trade Rifles have no brass hardware in the stock. It is not a great plains rifle. The Great Plains Rifle has two wedge pins, never used brass and also have a 32 inch barrel. The Trade Rifle has a 28 inch barrel. Also the GPR and old one mind you, has a 1-66 twist. The Trade Rifle has a 1-48 twist. That is an old rifle. But what throws me the curve is... the double trigger. The GPR has a double trigger while the Trade Rifle has a single hunting trigger. I almost wonder if that is not a Cabela's Hawken stock and trigger with a Lyman Trade Rifle barrel in it. Same company, interchanging parts. So that really would be my guess.
Someone purchased a Cabela's Hawken which has the brass hardware, and the double trigger. And then might have picked up a Trade Rifle barrel and put that in the stock. Either way, that is a very nice rifle.
That is my Lyman .54 caliber Trade Rifle Flintlock.
That is a .50 caliber Lyman Great Plains Rifle with a 1-66 twist.
That is a Lyman Great Plains Hunter in flintlock. The difference between the Great Plains Rifle and the Great Plains Hunter is the barrel.
that one is a newer Great Plains Rifle in Flintlock. I think that is the .50 caliber model and not the .54 caliber.