Ballistic Knife (5e Equipment)
From D&D Wiki
Martial Melee Weapons
A ballistic knife looks and functions just like a normal knife, but it secretly has a high tension spring powered blade that can be shot up to 30 feet away with incredible velocity. It is illegal in most countries.
Special. You can press a switch on the knife to cause it shoot outwards, making a special melee attack with it with a reach of 30 ft. which deals 4d4 piercing damage on a hit instead of its normal damage. Hit or miss, once you make this attack the knife becomes unusable as a weapon until you spend an action to rewind it.