This was an odd weapon test.
The Never Ending legendary effect was added to a harpoon gun and a 10mm, placed in qasmoke for testing.
The harpoon gun’s ammo type was set to none. Ammo type set a none makes this unusable in V.A.T.S.
Now the harpoons you pick up (from the guns) are more guns.
Fun bug, not a script.
FH DLC Needed.