sounds/wrblwnd/20mm_1.wav to _4.wav
Check6
HIT_6
M2
Tread
Veng
Vstart
Vstop

Like Dogg said, you only need the 20mm_1 & 20mm_2 for the guns, one for each 'set'
Hit_6: So it only gets hit one time?
M2: is for External gun sounds, it is needed but not in each folder, just in the main sounds folder.
Tread: Yes
Veng: Yes
Vstart: Yes
Vstop: Yes
You can also put in the 30cal_1 sound for the hull gun, as well as Explode sounds for ground battles, since you are on the ground. Hit sounds can be placed in there as well so each GV is different depending on armor.