@TimG
Typical large caliber U.S. Navy cases WWII to present are comprised of 40mm L/60 Bofors (Brass and Steel), 3 inch 50 cal (Brass and Steel), 3 inch 70 cal (Steel), 76.2mm Otto Malera (Brass and Steel) 5 inch 38 cal (Brass and Steel), 5 inch 54 cal (Brass and Steel), 6 inch 47 cal (Brass or Powder Bag), and 8 inch 47 cal (Brass or powder bag).
Observations:
40mm Both brass and steel post war. Biggest current user USAF.
3 inch 50 Brass from early 1900's thru WWII. Steel post war.
3 inch 70 Steel only.
76.2mm Otto post WWII. Early cases brass, later cases steel.
5 inch 38 cal Thru WWII brass, steel post war.
5 inch 54 cal scarce from WWII brass, steel post war. Only current Navy Gun. Norris was making steel cases in the late 80's.
6 inch 47 Brass only
8 inch 55 Brass only