i was shooting a 2213 alum. arrow; 30" length; and 4" vanes with a 100 grain broadhead but have changed to a 2413 alum.; 28.5"; 3" vanes and was wondering if i should change my broadhead grain weight up or down??

I think you should try what you have and see what the results are. Buying broadheads is, IMO, a total waste of money if what you already have will do the trick.

WELCOME to the forum.:welcome:

I would try what you have first. But if the others flew well you may have to go up on BH weight because of your stiffer spine with new shorter arrows. But give the 100's a run first.:peace: