Monty....Have you tried Heat Shrink instead of the teflon tape? It fits the 7mm tubes and fits snugly in the 30 cal. cases and 2117 arrow shafts. I glue it to the inserts with ca leaving a space between the ends and fill with GG when inserting in an arrow shaft, for the rifle caeses I fill with epoxy before drilling my flash hole keeping the epoxy just below the case neck and use the Heat Shrink to center the insert, again using GG. This is just the way I do mine. By filing the case with epoxy gives you something more to glue the insert to and as far as the Heat shrink, it has been working fine for me. Just thought I would share my way and maybe someone out there might find it usful for them as well.