I started thinking about the use for such an item... Should the items fly straight towards you, or do they turn in corners? That'd make them actually useful in other ways as another means of setting off traps. Here's something that might happen:
XXXXXXXXXXXXXXX
X..@...k....m..
X.XXXXXXXXXXXXX
X: Wall
.: empty space
@: player
k: kobolt
m: BIG mine, armed and dangerous
You summon the activated big mine!
The kobolt is hit by the big mine! The mine explodes! The kobolt is hit by the explosion! The kobolt panics! The kobolts left arm is severed! The kobolts right arm is severed! The kobolts left leg is severed! The kobolts groin is severed! The kobolt is severed! The kobolt dies with the sound 'BLLAAARGHFNARF'!
You are hit by the explosion! Nothing happens!