What part of the a muzzleloader serves as a platform for supporting the action and barrel?

The part of the muzzle loader that serves as a platform for supporting the action and the barrel is THE STOCK.
The fire arm is divided into three main parts, which are: action, stock and barrel. The action load and fire the ammunition and also ejects the spent case while the barrel is the part of the fire arm through which the projectile travels. The stock is the platform for supporting the action and the barrel and it is the part that is held by the shooter.