Addendum: After about 300 firings I now had some rivets - perhaps a total of 10. In terms of quantities, in which there were no problems, this is - I find - negligible. Buy I will continue the blanks.
2. Supplement: The 4th 100 box that I have used was complete scrap: The failure was approximately 50%. When cross-check with Sony, and TDK Maxell- blanks everything went well again, so was not a computer problem before. Well, given the first positive experience so I let the MediaRange blanks 3 stars. Buy I will but not only once more.