The most-often quoted figure that I've heard for shot-string length is approxamately 11 feet at normal Trap range, which would be about 35 yards or so. (16 yards from the house, then add reaction time.)
Little spheres are not very aerodymaic, so they slow down quickly - that's why shotguns have such limited range. If you figure that each pellet disturbs the air for the ones behind it, and that it's addative, the ones at the back have more 'work" to do.
very interesting video - the puffs of orange paint at the start are a nice touch....as anyone that has had that called, "LOST!" can attest!