Craft ammo in workbench - how to choose if it is created as a new ammo piece or adds on top of what is already in your backpack?

I keep creating ammo on my workbench and it keeps adding to my ammo in my backpack, which I don't want. I craft 10 ammo, and then I craft 5 ammo, and my ammo in backpack goes from 20 to 35. Instead I want a 10 ammo and 5 ammo to be available in my stash, so I can choose them individually for future missions. Is there any way to do this? Can we not create ammo in our stash of sizes we want?