Does it look like a GI front sight? Try letting some Kroil or something like that soak into it. Have no idea of the condition so maybe if well used in the field, maybe some rust in the joint? That would also benefit from the Kroil soaking or any oil for penetration and loosening stuff, like maybe you could get from a auto parts place. Being that it is a commercial gun, I have no firm idea of how it is configured in the front sight but it ought to come off at some point if it is slid over barrel and retained with a crosspin that you remove, like GI. And if you put on a bayonet lug, it might become an instant assault weapon in some areas!