I grouped my magnets in pairs and taped them together with masking tape. Along with marking the poles, helped them to avoid smashing. But also meant they wouldn't scratch the abs when removing them
Marc
Here's the boys blaster in operation with Brian's scope.
http://rs1262.pbsrc.com/albums/ii605/mistersea1/e11%20ref/20161226_150437_2_zpsrqvsaabc.mp4?w=160&h=160&fit=clip
Marc