MountainDevil makes a good point: you have a lot of wasted vertical space.

I keep bullets and powder in a locked metal storage cabinet. Locked because I have an 8 year old in the house. For large bulky items I picked up an adjustable metal shelve at Home Depot that looks like this:



Both the shelf and filing cabinet are to make use of vertical space.

It looks as though you have carpentry skills, so you could probably make shelves to save $$$.

And btw: You have a nice set-up and a great amount of space!