world war one - What was this 1917 shell casing used for

Bought this shell from an antique store. Would like to know the history behind it, as in what it was used for? (The casing is about 16 and 1/2 inches in length)

1962.033.010 - Shell, Artillery

Large calibre markings (The Western Front Museum)

Large calibre markings (The Western Front Museum)

World WAR 1 Trench Art Shell Casing Bullet Leaves Hammered Carved 1917 Paris, France - Canada

Were the howitzer, about 100mm brass shell cases from WW1, reused or just wasted after having been first fired? - Quora

1917 75 Mm Ww1 Mortar Shell Casing