[oregeezer]

I don't have any trouble with the gerund and the participle. As a speaker of American English for over 75 years I would not recognize either of them! The sense of both sentences is the same (as are sewing machine/ machine that sews and dog for hunting/ dog that hunts) the grammar is of little practical use except as a device for teacher's who are unsure of their ability to utter good English sentences. Don't worry about the tense; teach them the sense!