Ah, I didn't realise you were talking about Dredd. But the answer is the same; the Lawgiver fires one shot at a time in normal usage, whichever ammo it is using, but cone and spray type exploits use full standard execution clips.
Its a general question and the Lawgiver was just an example that tracking ammo is a thing in the game.
In case I want track ammo, but using automatic weapons cause a little ruleswise headache. On the one hand, you may shoot areas, like throwing a grenade in an area (which you have to count), but on the other hand, clips of automatic weapons tend to be bigger like 20-50 bullets.
Crazy idea: area effects of automatic weapons cost number of bullets equal to feet of the size. So a Burst 2 costs 10 bullets and a cone from the auto trait costs 30 bullets.
I am working on my Mass Effect rules adaption of WOIN. The game has collection of very distinct assault rifles and submachine guns (for example different sizes of clips). The ammo tracking should create a distinct feeling for every weapon.
Edit: It also helps to determine which weapons gain the auto trait, if you know that a weapon must have a clip with at least 30 bullets. Weapons with smaller clips gain the burst trait.