Quoting from a dealer of the IBS barrels;
“15/16" Octagon barrels fit the T/C 15/16" Hawken Pennsylvania Hunter & Carbine, Cabela's Hawken, Investarms Hawken, Lyman Trade Rifle, Lyman Deerstalker & Carbine, by adding an extra barrel lug it will fit the Lyman Great Plains Rifle.”
Disregarding...