This is a thing I never gave any thought about until about half an hour ago when I couldn't unfold an equipped mp7 I had hot keyed from a 2x1 slot in my rig. I could not unfold it because it would be 3x1 in inventory, thus too large for the slot. Even if it's equipped, it sits in that slot.

Obviously the biggest question about this would be "what about when you unequip the gun?" I say just disallow the player from unequipping the unfolded gun and give a message saying that it must be folded back up to put it away. Alternatively, it could drop the gun like a magazine would be dropped when the rig is full, for quicker switching to another weapon.

This wouldn't be any meta-changing addition or even something half of players would even notice/take advantage of. But I don't see the realism in not being able to use my stock because my weapon would be too large for the pocket it's not in.

EDIT: Some rephrasing for clarification