And simple logistics of making ammunition.

Making arrows is quite an involved process that requires a whole bunch of quite specialised skills. Especially arrowheads, which need to be made by a blacksmith of some skill, and expensive resources (iron/steel). But making the shafts also needs some woodworking skills, first you need to select the right wood, then it has to be straightened and given the correct shape. The fletching has to be of uniform size, too, and needs to be attached securely and precisely, or the arrow won't fly straight.

Making powder requires the correct grinding and mixing of three simple ingredients, which requires some skill, but can be easily done in bulk. The biggest skill involved is not accidentally blowing yourself to smithereens. Casting lead bullets of uniform size and quality in bulk needs the skill of lighting a fire and handling a pot, in order to melt lead and pour it into a pre-made, reusable mould. This can also be done in the field with very limited equipment.