Field flask id

[Toccoa]

Hello,
I am trying to solve a small mystery. I have a small, zinc canteen. You could call it a hip-flask.
It measures 15 x 11 cm. It has scew cap. No markings. One side is convex, one side is slightly hollow.
Might it be home-made civilian? The flask was part of an old ww2 collection comprising mainly of Dutch, Uk/Canadian and some German items.
What do you think?
Thank you for looking, regards.

[08SMLE48]

Interesting, I’ve never seen anything like this. The flat side really throws me off. Hopefully someone comes along with an ID of it!