I think the point here underdog is that you haven't given any plausible reason why it shouldn't be taken off the timer other than "unforeseen consequences".

You said it would be too powerful on the opener. And something about AoE. But what you've failed to realise is that you can already keep ammo up indefinitely for both those scenarios (or any, actually) just by using quick reload. The ammo timer is 30 seconds, quick reload has a 15 second recast and refreshes the timer. All this change would do is make it so you don't have to constantly spam quick reload to keep a stack of 5 ammo up. Which as it stands doesn't make sense anyway because ammo generally doesn't magically vanish from guns after 30 seconds.