German WWI Artillery shell casings brass and steel Identification

Hello and thanks for taking time to read this, I have two artillery casings, one brass and one steel that appear to be the same size, can anyone confirm that caliber? 77mm? Too, did Germany resort to steel late in the war? Thank you!

Stewarts Military Antiques - - German WWI 7.7mm Artillery Shell & Casing, 1917, INERT - $225.00

German WWI Artillery shell casings brass and steel Identification

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