I recently ordered half a metre of green 0.8 GZK flatbands to try with 8 and 9.5mm steel balls. I followed some advice I found online of a 22-15mm taper for the 9.5's, and upon fitting the bandset and testing it, the power I got was incredible. From about 15 metres away, I sniped a tin soup can filled with water, and the ball went straight through, knocking it a good 4 feet up in the air, without slowing down that much behind. The shots that missed the can embedded themselves about 1-1.5 inches into the rotting birch log below. Since I still had 8mm steels left, I made a bandset with a 15-10mm taper, excitedly plopped it into/onto the frame and gave it a go. Again, straight through the tin can, although they lacked the satisfying wallop that the 9.5's give. Great adaptable elastic!