What is It?

[Marine A5 Sniper Rifle]

This is a picture of Canadian snipers training. What the heck is that device they are using?

51384

[Ken The Kanuck]

Kind of looks like a training mount to me, the solider is centre to the rifle, could it be that the device sets the elevation to a desired height and this familarizes the shooter to the correct placement of the rifle sight?

Just a guess mind you.

I do remember seeing a device which used a spring and nail to train shooters with a Lee Enfield, maybe ammo was considered expensive back then?

[Marine A5 Sniper Rifle]

Beats me. I never seen anything like it.

[barretcreek]

Thinking same as KTK. Wheels look oval.