I used the poly rope he uses and I put 36" of rope in my 25 7/8" arrow. I went from 346 gr to 592 gr. I tried useing about the length of the arrow and an extra 4"and was getting erratic flight. I believe do to the rope packed down in the shaft and was sliding on the shaft. when I release the rope would slide towards the noc making it act stiff with the weight being in the rear end of the arrow. Then it would slide forward towards the front of the arrow making it act week. So I added more rope till it stoped sliding. The was solved and flew straight. I weighted the rope and it weighed about 4gr per inch. It has some trendous penitration, I shot with my broadheads at a 4ft Styrofoam block and the arrow with the rope penitrated about 3/4 of arrow length deep. The arrow with out rope pentrated about 1/3 the length of the arrow deep. They were both shot from 20yds.
I forgot to mention that my bow is 42lbs at my 24 3/4" short draw.