If you are talking about consumable, Activate ammunition like the Bane arrows, Ooze Ammunition, ect, my table has run that as 2 per Reagent.
That said, they are not very good, and you will get more out of making bombs for the Alchemical Crossbow to get you through the early game.
The Gunslinger's Munition's Crafter only gives the 10 per batch for the L0 ammo, basic black powder shot.
The fact that the Feat leaves special leveled ammo per reagent unchanged is pretty telling as far as precedent goes.
If you want to ask your GM to buff said alch ammo via making more per advanced alch, that's a fine thing to do.
Advanced Alchemy sets the batch size to 2.
For each batch of infused reagents you spend, choose an alchemical item ... and make a batch of two of that item.
If you spend downtime to craft the items, then it would use the batch size for the consumable or ammunition that you are creating. 4 if not specified elsewhere, but ammunition can use the quantity count in the ammunition purchasing table.
I do want to be sure to mention that, ESPECIALLY now that the remaster allows for all commons to be crafted w/o formulas, an Alchemist preparing a few injury poisons to use on ammunition each morning is a good to great idea.
Poisoned ammo is a no action enhancement to existing shots, and if you check the on-level options, there's usually one that is +1 or +2 *above* your class DC. If you use something with a magazine, that's an issue, but aside from that, a poisoned bolt is often better than trying to make ooze ammunition, ect, work IMO.
Goblin Burn It might mean that Elemental Ammo Fire is potentially worth it as the 1 persistent dmg will be boosted by 2x, however, at a glance I would still use the Alch Crossbow loaded w/ fire, as it's still alchemical and should be compatible.