The bottlecap mine is a powerful improvised weapon. It functions like other proximity mines, activating when any land-based target approaches within 4.6 feet and detonating within 3 seconds, though the target's explosive skill (or lack thereof) will modify the timer. The explosion will maim and kill anything within its 12-foot blast radius once the timer runs out. Like other placed explosives, it cannot be used in V.A.T.S.
Alice McLafferty mentions that some individuals use caps inside explosives, in reference to the bottlecap mine, though she also dismisses such individuals as damn fools.
Note: this item is also craftable via a dialogue option with Veronica, or with ED-E (with at least 1 rank of the Camarader-E perk).
Ranger Station Charlie - Enemy-placed mine; must be disarmed. Located in the room to the left of the entrance behind a pair of fire extinguishers. Only appears after speaking to Ranger Andy about investigating why he has lost contact with the station, or starting Return to Sender.