I used the 5/8" backer rod cut into 24" pieces with 1/2" hot water couplings as dread rings painted in hammered finished copper and they seem to have an excellent movement to them, the only thing that stuck to them was black plasti-dip, paint & latex both peeled or flaked off, see for yourself and hope this helps
For anyone else possibly still looking at this, has anyone tried batting foam and latex? I remember seeing it on FaceOff once (season 10 episode 1 I think?) and the swing/weight was perfect but i think they were kinda big. Debating giving it a go, maybe I'll follow up in a bit.