First class run by colt - the one going off like a shot
I believe the answer is:
air gun
'going off like a shot' is the definition.
I can't judge whether this defines the answer.
'first class run by colt the one' is the wordplay.
'first class' becomes 'ai' (Ag - top quality).
'run' becomes 'r' (cricket abbreviation).
'by colt' becomes 'g' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'the one' becomes 'un' (I've seen this in other clues).
'ai'+'r'+'g'+'un'='AIR-GUN'
Can you help me to learn more?
(Other definitions for air gun that I've seen before include "In a rug (anag)" , "Weapon with small shot" , "Weapon that propels a projectile by compressed air" , "Pellet firer" , "Rifle firing pellets" .)