Ok guys. Thanx a lot for your interest! I met the owner today and had some talk about the shell. He told me that is totally empty in the inside. He also told me that he thinks if it might be post war. It's more likely to be WW2 era Italian naval shell though. It used to have an outside layer of the material shown at the updated attached photo. He removed it all except the one shown in the photo (he formed Leros on the shell!). So the fact that the shell used to have an extra layer might be helpful. We couldn't go and measure the diameter. I'll try to do so soon.Please check the new photo below and the Leros shape (in order to admire the style/idea of forming Leros on a shell found in Leros).