Well maybe its because other brands need other barrel makers that know how to build a barrel suited for a conical to shoot properly?

GM barrels are kind of expensive though and i couldnt see putting a $150-250 barrel on a cva bobcat .. Just wouldnt make any sense. Now if i were building a full out custom muzzleloader then yes, i'd look for an after market barrel liike gm. Who'd pay $4-5000 on a custom muzzleloader that has a cva or tc barrel? lol not me.