50/75gr. brass inserts and arrow balance

[Modad2010]

So i have a 54" Toelke pika - 40# at 26.5". I have now great arrow flight with full length centershot 600's using 75 gr. insert with 145gr. points. (50/75 break-off inserts) I also have one arrow that is cut to 29" flying great with the 75gr. insert and 175gr points. Then I have a 28" shaft that wouldn't shoot any point 100 - 250 grns. worth a damn using the 75 gr. insert, but after breaking the insert off to get it to 50 gr. I get perfect flight using a 200 gr. point. (seems to fly even better with a snuffer that weighs in at 198.4 gr) I am wondering if the extra length of the insert at 75 stiffened the arrow too much and by breaking off the insert and moving that weight to the point somehow evened out the balance. The fletching on the 28 incher would corkscrew all the way to the target with the 75 gr. insert no matter what the point weight. I really like the idea of using a 200 grain head due to all of the great broadhead options available in that weight. Has anyone else ever had something like this occur?

[ScottinPA]

The insert length does have an effect on the stiffness, similar to footing.  Look at Stu Millers calc.  He accounts for insert length over the standard.  Change it in the spreadsheet and you can see how it changes the spine.