I found this stuff at the hardware. (Talondale found it online)I have been putting it in my arrows to dampen the sound. They add about 10 grains for a 30 inch arrow. Nice stuff. Maybe everyone knows about it already. I didn't so I thought I'd let ya'll know.
http://www.dap.com/product_details.aspx?product_id=356
great idea
Picked some up today. Need to figure out how to get it inside the shafts as it's a smidge tight. Took an arrow in with me to the hardware store to see if it would fit and I could get the end in but it looks like it will take a little work to fit inside a XX75 500 (2016). Almost went with some window screen spline, the .190" was close but a little loose and heavier than the backer rod but you got 100' for the same price of 20' of backer.
i used great stuff foam
Isn't that a little messy Ray? I can't even look at that stuff without getting it all over me, even if I wear gloves.
Try sticking it in the freezer for an hour. Maybe a little easier to push it into the shaft.