Looks well organized. In mortar competition we are required to have individual main charges and boost charges each in individual containers, with the main charges marked differently from the boost charges. We are not allowed to have bulk powder in the ammo box. We do this because there are a lot of mortars firing relatively close to each other and if a spark were to get to some open powder the most (hopefully) that would be set off is one individual charge instead of a whole can of powder. If you are the only mortar on the range and you are working up charges with an adjustable powder measure you are probably all right as long as you don't have any open powder, and close the lid on the box before firing.
For the cannon have your charges made before you get the range for the same reasons as the mortar, and you will also find it more convenient.