^^^

Historically, "gun axes" functioned just like bayonets except instead of a piercing blade, a single bladed Axe head was affixed to the front of the gun near the muzzle. Out of bullets, take your gun and swing it like an Axe.

Same general concept could be used to design FF style gun axes, in which the shaft of the axe is the body and barrel of the gun part. For some reason I see the melding of a pump shotgun with a large two handed battleaxe being the most fitting combination.