Are you asking for number 1 or number 2?
1.) Damage - 20 cannon round have hit your ariplane
Damage - 53 MG round have hit your airplane
2.) MG - 122 rounds remaining
CN - 25 rounds remaining
You are forgetting in your english to describe the source or action of the ammo information so your audience does not have to guess. You are assuming your audience understands your request by refering to the damage window. Number of bullets has two meanings becasue you are not including an action descriptor but, instead a common game function "damage window".
What is your native language by the way?