Pretty much what the title says. Because why not? You cannot use another ammo synthesis until the timer runs down, primary ammo is typically plentiful anyway, followed by special ammo which is rarely in short supply, and heavy ammo is doubtlessly useful but also very expensive to synthesize, and is also variably useful and efficient depending on if you're using rocket launchers or machine guns. Add to that the differences some gear creates with ammo capacity-increasing perks, particularly with Heavy Ammo capacity-increasing perks, you have a wildly erratic range of gains and efficacy for these universally costly and time-locked consumables. If these were made to also generate additional ammo at reasonable rates that were appropriately tailored to the ammo pool/weapon being used, the ammo synethesis experience could become a lot more enjoyable. Between wipes in Raids, the immediate failure tends to also hit ammo you're holding, but if you were steadily generating more through the duration of the ammo synthesis, generation a fresh rocket every 30 seconds, or a round of machine gun ammo every second or two, you'd be ready to go again without much fuss. Whatcha think?