17 Pr steel ammo crates

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For the rest of MLU, I'll answer the question. Old .303BR small arms ammo used to come in crates much like the one pictured.

The wooden crates had a stiff metal strap across the end pivoting on two screws. Take out a safety pin, sometimes on a string, and the straps roll off the ends of the top panel. The contents are now exposed.

The metal cannisters are much different. The two recessed heads attach to cross locks. Unscrew the handwheels, the tensioners loosen, they can be turned out of the way, and the end panel removed. Later 76.2mm CVRT rounds came two to a case with similar closures. There would be some sort of dunnage or packing inside to hold the rounds from rattling.