My first bow was a 43# ash american flatbow. I was shooting ash shafts at a friend's recommendation because they "wore like iron". Yup, shot that dozen arrows for 2 years before I ended up losing most of 'em. Broke only one. Then I made up a dozen from sitka spruce. Couldn't understand why I was now hitting 2 ft higher all the time. Went back to the ash shafts and realized I was shooting rainbows. To hit a 20 yd target I looked like I was on the Bonneville Salt Flats for the International Flight Shoot!!!!
When I went back to the sitka spruce shafts and re-learned to shoot, I hit more things at various yardages because I didn't have to compensate for wild arc arrow flight. What I am going the long way to say is that you don't always want to add weight to an arrow. Yes, I agree, the physics proves a heavier arrow penetrates more deeply. But if your arrow is so heavy you have to sky-launch them, accuracy suffers and all the penetration in the world doesn't help poor accuracy.
It wouldn't hurt to get your arrows weighed. If you are shooting more than 13 grains of weight per pound outa that 40 lb bow you may have problems. A little more speed from a 12 grain/lb draw weight would be better, but even 11 grains wouldn't be too bad. When you get down to the 10gr/lb then you are into the target shooter range and may not get enough penetration.
But no matter what weight you choose, fletching style, cresting, finish, glue choice, what-have-you....get'em scary sharp. Make 'em so sharp you get nervous reaching for them, so sharp that if you cut yourself you don't feel it until you are weak from blood loss!
