RE: how many grains of arrow do u need to drop a deer?
 

The weight of the broadhead has absolutely nothing to do with killing power. A head weighing 3 grains would kill just as quickly if you could find some magic material that would be durable, and large enough at that weight. The problem is matching them to your arrows and setup to make them fly right. A 40 grain broadhead would do fine, but good luck matching it to your setup.

RE: how many grains of arrow do u need to drop a deer?
 

BobCo 19-65, Great website! Thanks! So much out there and it's nice to have guys narrow down a search for you. I will be doing my calcs here too.