If I want contact/pressure between a forearm and barrel, I use neoprene O-rings. Neoprene is soft enough to contour itself to any irregularities and provide constant pressure. It works for me, particularly so with mannlicher-style stocks where the barrel and forearm cap may come into contact with each other.
I placed a 3"x3/4"strip of soft weatherstip foam in a free-float barrel channel one time and it worked wonders.
