Yes, it’s for a bayonet!
But it’s not common, a little more maybe towards the German border. But not at all from my home.. it is very recently that the hunters started using rifled weapons.
I think it is either a weapon of venery, or a weapon for the colonies in Africa.
Bombonnel, a very well-known panther hunter, used a Lefaucheux pinfire, Cape-gun style shotgun. He was shooting a mix of bullets and buckshot, with one hundred grains of black powder. It’s rather curious, but it was apparently effective.