I've fitted brass tips to fiberglass rods also; but use another approach. I use the brass tip to measure how much needs to reduced, mark with a fine tip Sharpie. I place blue painter's tape at the mark, I then take a tubing cutter and make a series of cuts from the tape to the end of the ramrod, estimating how deep to go with the tubing cutter. I take a sharp chisel and remove some of the fiberglass, top, bottom, then the 2 sides, then make it octagonal. then I take a file and make it round. Trial and error fit from then on. I epoxy the tip on, then drill and put a small brass brad thru the tip/ramrod. I use nippers to cut the brad and peen it,then file the brad smooth. I use a fine grit sandpaper to remove file marks. I use the same method on wood ramrods too.