Belgian shell, but an odd one

[Pickelhaube]

This is a shell i bought last year. It's the shape and size of a Belgian 77 mm shell, but yet its an odd one. This piece should date from just before ww1. Some people said it was an experimental shell while other said the piece had instructional purpuses. I think it's the 2nd option, but maybe somebody here can shed a ne light on this. The only marking on the shell is "R.10"

Greetings

Pickelhaube