From Guns and Gears, page 154:
"Unless otherwise stated, these rounds come in packs of 10 that cost 1 sp and have light Bulk. The only weapon in this section that works significantly differently is the growth gun, which grows back a gob of its own ammunition once per round, ensuring you always have enough ammunition to fire a shot every round."
They do not seem to be either magical or alchemical ammunition, which means all you need is the Craft skill. Munitions crafter won't work here since they're not alchemical ammo/
Guns & Gears pg. 151
Because making rounds of firearm ammunition requires creating black powder, you need the Alchemical Crafting skill feat to make them.
Munitions Crafter
If you use a batch of infused reagents to create basic level-0 ammunition such as black powder cartridges or black powder doses, you produce 10 rounds of ammunition.
Yes, you can use Munitions Crafter to make ammo for your Beast Gun.
Even though beast guns don't use black powder?Guns & Gears pg. 151
Because making rounds of firearm ammunition requires creating black powder, you need the Alchemical Crafting skill feat to make them.
Munitions Crafter
If you use a batch of infused reagents to create basic level-0 ammunition such as black powder cartridges or black powder doses, you produce 10 rounds of ammunition.
Yes, you can use Munitions Crafter to make ammo for your Beast Gun.
Ah, I missed the note under Beast guns that said "they rely on magic rather than black powder" and just saw "Beast guns aren't loaded with the same ammunition as other guns, but they do still use ammunition". Yeah, it seems you'll have to buy them. Sorry for the confusion.