Ammo casings is one of the items one often find while searching on battlefields. I have a thing for damaged and exploded casings of any caliber and am always happy when I find a torn example. Here is some of the ones I saved this season.
Two WW1 7.62 Mosin casings.
Two Russian 12.7mm casings from IL2 Sturmovik or the DP Machinegun.
A German 20mm FLAK.
Russian 14.5 mm for a heavy machinegun.