Lyman™ Great Plains Rifle Signature Series - .54 Caliber Percussion - 6034001The . 54 Caliber Lyman Great Plains Rifle Signature Series Muzzleloader is the latest iteration in the Great Plains line of rifles. Lyman has offered the Great Plains Rifle since early 1980. The GPR was engineered to be authentic in design and accurate on the range and in the field. Many of the standard design features of the Great Plains Rifles will be carried forward in the Signature Series, which is made in cooperation with Davide Pedersoli of