People in Mongolia today can still hit things with a bow and
arrow from a galloping horse. So a bike/rifle combo should
theoretically be "do-able". Especially if the distances are
short.
Ever ridden a horse? And No, the gals of Shanghai don't
count ;)
Even over relatively rough terrain, the gait of a horse is
fairly rythmic and predicatable ... which allows for reasonbly
accurate trained marksmanship.
The bike OTOH, will only be able to be effective on artificially
level ground. Even the rugby "fields" in Farrer park will
bounce around the rider too randomly for effective fire.
My 2c