Bolt double? That's what one might be aiming for! (4)
I believe the answer is:
dart
'bolt' is the definition.
(thesaurus)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for dart that I've seen before include "Small pointed projectile" , "Slender pointed missile" , "Move quickly and suddenly" , "Small arrow" , "Arrow - go fast" .)