"will an arrow fly right with a 50 grain point?" It might if you make it longer. This is kinda like the thread where Eric Jensen is asking about spine advice. To make a lightly spined arrow which is 8gpp, you either need a really lightly spined shaft,or a really long shaft. Either that, or just hide the effect of an overly stiff arrow by using big feathers. Bamboo may not be the best choice for a shaft like this- the skinny ones are often just 1 year old and therefore easy to break. As Jack says, dowelled fir or Sitka spruce may be good.