Wow I actually liked it a lot, so much I may even consider playing it again!
I think it might have been something obvious and I missed it, but after opening the panel, I notice I can drag gun, armor, etc. I think I get that and it works, but how do I drag the corresponding bullets into the corresponding gun to load it? I am pretty sure I was matching up the right kind of bullets with the right kind of gun. I tried pressing R and nothing happened as well. What might I have missed?