I guess most of us use arrows that run 8-12 grains per pound -some go lighter and some go heavier -with 10 ggp about average. Try one of your carbons and see how the bow feels in your hand. You put too light of an arrow on a longbow and it will let you know about it. You'll swear the handshock running up your arm to your jawhas made a couple of teeth swap holes. [8D]

With wood and aluminum, you need to get within 5 pounds of the spine your bow likes with the tip weight you want. With a 20 pound spine range, carbon really won't do much to tell you what spine your bow would like though. You'd be able to narrow it down a lot better with aluminums.

Check out the spine chart at Arrows by Kelly. It seems to work really well for most folks. http://www.arrowsbykelly.com/Spine_Charts.htmlBut again, just like all arrow charts, it's only a starting point. The only way to know for sure is to experiment with different spine arrows. Usually won't be more than a couple of sizes either direction from what the chart calls for.