I use for carbon shafts isolation foam that is used under laminated floors. I cut a rope of it of the lenght of my arrow shaft. You can cut it very easy on the weight you want. I wanted 45 grains, which resulted in a width of 2/5 of an inch.
Then I get a wire or thread through the shaft, knot it to the foam, spray it with silicone spray and pull it trhought the shaft by pulling on the wire or thread. You have to use silicone spray in order to make it move smooth trough the shaft. It doesn't affect the spine, stays on it place and I like it.
After a few 100 shots it might crawl towards the point a little bit (like 4 inches) but I saw no negative reactions from the arrow.
This an interesting thread!
I dont opload frontweight, because I want to keep my FOC low because I am a 3D shooter. Shooting wit 25% FOC on 60 yards is not the way.