Not really, because you can get away with less. The 420gr. you refer to is AMO rating.....6 grains per pound of arrow pull. You can go to 5, but no lower. Besides, I was shooting a 29" Easton Carbon Excel w/ 100 gr. tips and it was checking in at 410 gr, and the Excel is a light carbon arrow. If you step up to an Axis, let's say, in a 340, your raw arrow @ 29" would be 276 gr. Add your 100 gr. tip, insert, fletching, nock and so forth..you'll be in that 420 gr range, if not more.



If you get right in the ballpark of 400 gr. you'll be just fine.

The problem with the math you've done is that you didn't take the insert, nock and fletching into the equation. Check out www.eastonarchery.com and mess around on there. You'll learn lots from arrow weights to all sorts of stuff.