I've noticed shooting Simmons broadheads like the intercepter I can go a little lighter in point weight and I'm wondering since it is a long broadhead it is weakening the spine a little or is it something else?

Theoretically, it's moving more weight further out on the end of the shaft, so it would weaken the shaft slightly.  Practically, not enough to make a difference. 

I agree with Orion.  Only the part of the broadhead that sticks out further than a field point of the same weight will affect spine more than the field point itself.  The amount of the broadhead sticking out to the sides has no more effect on spine than a field point of the same weight.  So unless you have an extremely long broadhead, the effect should be negligible.

A tip I just learned on here...make a broadhead "bareshaft" with the fletching cut down to 1/8", to check the tune.

Absolutely.

Not only is the weight moved a little further out but the overall arrow length is longer. Look at it this way, if you had two arrows with the identical field tip weight; the longer shaft will shoot weaker. Shorter arrows will act stiffer all things being equal.

My own test with broadheads on 1/8" feathers (on stripped quills) usually shows the broadhead needs about 20 grains less weight to bareshaft the same as a field point 20 grains heavier. Vented heads for reasons I don't know shoot a little more stiff than non-vented heads. Maybe a different bow weight or draw dynamic would change that; but this is how it works for me.

As was mentioned before... this is minor variantion that is unlikely to effect the good flight characteristics of a feathered shaft. But those who want a tuned arrow to the highest degree possible might be interested in knowing.

Quote from: BAbassangler on December 16, 2025, 09:25:30 PMA tip I just learned on here...make a broadhead "bareshaft" with the fletching cut down to 1/8", to check the tune.

I have to try that...

I learned this many years ago from my friend and TG member Art Butner(artcher1). Art was an expert in arrow making from simple cane and hardwood shoot arrows to commercial or homemade doweled and split shafting.
The spine weight given on a particular bare shaft is for a complete arrow of 28" with a 125 grain point up front. At least this is for wood arrows. I'm, not familiar with carbon or aluminum arrow shafts. You can change the actual spine by adding or subtracting length and adding or subtracting tip weight. By shortening the length you increase the dynamic spine value of the arrow and by increasing the length you decrease the dynamic spine value by 25# per inch. By increasing the head weight you decrease the dynamic spine value of the arrow and by decreasing the weight of the head you increase the dynamic spine value by 25# for each 25 grains of point weight.

Quote from: Pat B on December 17, 2025, 10:27:47 AM25# for each 25 grains of point weight.

Even I can do that math...I'm switching to wood!

 "by decreasing the weight of the head you increase the dynamic spine value by 25# for each 25 grains of point weight." Nope. Must be a typo there somewhere. 

Sorry, just mean it's a grain/lb...easy math.  Al and carbon; each shaft is different, and I haven't had one yet be 1:1