The round on the left is a British .303 inch ball Mark VII. If you give it a good clean you should be able to read the headstamp.
The clip of five are German 7.92x57mm ball rounds as you supposed. They were made in August "(8") 1916 ("16") by GM, who as far as I know have not been positively identified. The "S67" idicates a brass case with 67% copper content.