Ive you ever got attacked by a gunship in arma you will have heard the explsions of the cannon rounds hitting behind you as you try to run into cover. Now ive you got into a firefight and started taking 40mm grandes from a rifle mounted launcher youll notice the sound is the same.
The cannon round of a helicopter has no sound for its speed, it has no crack or wizz sound, its just as ive something explodes. and does not sound like a actual HE bullet.
go into editor, place a unmaned marshal (nato armored) an place a civilian with zeus being set as player about 300m away (either set to go moe or behin a tank as cover). now using zeus place a nato grenaier besides the marshal, take control of him an shoot a grnae at the civilian, an quickly switch back before it lans to hear it land.
now mount in the marshal, put own a csat soldier somewhere an while howering close to him in zeus tell the marshal to engage him.
Now compare the 2 sounds.
-40mm grenade with about 80m/s, not very much of a woosh.
-40mm cannon shell, with about 10 times as much speed, still no woosh or auible punch behind it as far as speed goes.
Helicopters should rather use 30mm instead of 40mm cannon. But it do not change the fact that such projectiles are supersonic unlike 40mm low velocity grenades used in underbarrel grenade launchers.
Yes there should be some kind if crack. And it should be even louder as those projectiles are bigger, much bigger.
Gentelmans, "panie i panowie", In arma sieries there was allways some sound mood required to fully enjoy gameplay. In arma 3 there is 2 sound mods, fuuly compatibile with other mods. JSRS2.2 and JSRS3 Dragon Fyre. Its best and only solution. Add lots of sounds for events happen in game like tank crushing some fence, hitting some stone, sonic cracks ( i recomend download also JSRS soniccrack tweak for some less loud sonic cracks) and many, many, many more. It is big size, but trust me, its worth it. It is also updated, but currently had no errors since 1.36. BI should recomend this mod, or talk to mod devs and buy it from them and make integral part of game.