Interesting finding. Where from?
Strange tail units, separated linked by metal straps to the body of the bomb were sometimes seen in the 1930s:
here's an example from a bomb devised for the KNIL:
View attachment 180019
To the best of my knowledge, the Jouhandau 75mm projectile had a wooden tail attached by metallic straps ("tenons") to the body - but I have never seen a photograph of it, the mortar itself being relatively scarce.
For the lovers of ww1 Trench artillery, there are 2 very nice, of surprising good quality, video documentaries taken during the French army trials of the various materials, probably in 1917:
https://imagesdefense.gouv.fr/media/catalog/product/video/87753.mp4
https://imagesdefense.gouv.fr/media/catalog/product/video/87754.mp4
(the second one is the best)