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!

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Find many great new & used options and get the best deals for WWI Trench Art Large Brass Artillery Shell 75mm Oak Leaves Acorns Hammered Vase at the

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