Very nicely done on the tommy gun mag case.
One thing - once the size of the case gets past one gun, I'd go with a frame (at least on the hinge) out of a hardwood rather than pine or fir. I'd suggest poplar b/c that's dimensionally stable and easier to work than, say, oak. And for the really big/heavy cases I might consider box joints on the corners, rather than just a couple screws, and floating the bottom into a rabbet.
But that's just me. I tend to overbuild my stuff so I don't have to come back and fix it later.
