Arrow weights
 

I don't find information about arrow spine and weights for crossbow like is available everywhere for compounds and longbows. My crossbow was advertised with a speed of 320 or some such, maybe a bit more. Three arrows came with the package, and they chronograph at 280. Very accurate though. I called the manufacturer, who told me (you wont be suprised), that if I want more speed to use lighter arrows. OK, fine. So what weights are proper and safe for a round wheel 150 pound crossbow? Reading further, the book warns against using improperly spined or weights of arrows, but that's no help. Any info on crossbow arrow selection will be appreciated.