So just curious when i picked my arrows i had them spined for 100gr. heads. According to the chart i would still use the same size arrow for 125gr. heads. So how much different in spine could there be if i make the switch?
No way to tell without even knowing what kind of arrows you're talking about. Go to
www.bowjackson.com and click on the Arrow FOC and Weight link. Choose the brand of arrows you've got, then just plug in your numbers. It probably won't be exact, but it'll be close. You can use that tool to build all kinds of model arrows - see what'll happen to your weight and FOC if you switch from 85 gn points to 125 gns, or from 4" vanes to 5" feathers... all kinds of different combinations.