Hi Peter,
Not done much riveting but one occasion the formed heads had a sort of collar and the pre – formed heads likewise, if I remember, it was many years ago. I was advised by a fellow member who trained as a school metalwork teacher to buy a riveting snap set from the same source as the rivets. Then one should fit the other properly. Unfortunately my supplier at that time, ol' Chas. Kennion now long gone! So I would need to try what I still possess or get new lot.
Regarding your query, if in doubt, try out what you want to do on some spare bits of identical metals and of course, same thickness(es). You could have some difficulty as JasonB said above, asthe metals are dissimilar, one being soft as chewing gum and the other considerably harder.
HTH and good luck,
John