# How does incease in draw weight affect arrow spine??



## scruffy dog (Sep 10, 2006)

I have walk back tuned my bow, ultratec, for center shot, and all has been shooting fine for months, draw weight about 53lbs. If i wind in the limb bolts a turn to increase bow weight to about 55 to 56 pounds, how will this affect the center shot.
I know the result will be to make the spine seem weaker, but will a weaker spine arrow shoot to the right or left, or will center shot remain the same.


thanks.


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## 3D-Nut (Jan 26, 2007)

It can be hard to predict. That couple of pounds might make a big difference if you were borderline to begin with. Sometimes a minor change will affect your tuning quite a bit and other times it just boils down to re sighting it in. If you must increase the spine, you can shorten your arrows or install lighter tips to bring it back to the same spine. If it wasnet border line to begin with, it may very well stay perfectly center shot. Especially if youre just shooting field tips, often times an underspined arrow will still shoot decent. However, when you add a broadhead to the mix, that underspined arrow will manifest itself rather quickly. Any time you make a change you should verify it with a field test. By far the best thing to do is shoot it and find out!


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## scruffy dog (Sep 10, 2006)

thanks,
i set bow up for target, shooting easton acc, but increasing by about 3 to 4 pounds seems to have affected the grouping, not as tight as before, and i'm just trying to work out if the spines are now too weak, or if i need to retune something.


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## VFX_Fenix (Feb 8, 2007)

You may want to consider a bare shaft test. That should give you a pretty clear idea of what's going on with your arrows. I was shooting some 2014's that were grouping pretty well for me, went to shoot a bare shaft and had the shaft hit 5' to the left of my group. If you're arrows are too weak they'll land to the right of your group.

Right handed shooter - 
Weak -> Right
Stiff -> Left

Reverse for the South Paw.


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## Deezlin (Feb 5, 2004)

scruffy dog said:


> thanks,
> i set bow up for target, shooting easton acc, but increasing by about 3 to 4 pounds seems to have affected the grouping, not as tight as before, and i'm just trying to work out if the spines are now too weak, or if i need to retune something.


A weak spined arrow will not show noticeable variations of left or right for a release shooter. If you read Easton's Tuning Guide section on arrow dispersion, you will find it has an effect on grouping.

A weak spined arrow, for a release shooter, will oscillate longer in flight than a properly spined or stiff arrow will. If the flight group of arrows are consistantly of the same spine, but weak, over distance they will average out to a very constant flight path. The same group of arrows will however usually have slightly different frequency of oscillation and will produce extremely large groupings at close distances.

Basically, if you are shooting 20 yards at a given poundage and up the poundage, and your grouping opens up, your arrows are going weak for that poundage. The steering action of a broadhead makes this much worse, too.

This is one of the little tricks that long distance target shooters use to get the most out of their arrows for distance. Now, let me clear up one other point. All shooters should use a properly spined arrow for the poundage, they are shooting. Neither a stiff arrow or a weak arrow will be as forgiving of a bad release. Finger shooters should be more mindful of this than a release shooter. The release shoot can shoot a stiffer arrow because he usually has a more constant release. But, he is giving up some forgiviness of the spine by doing this.

For close range hunters, they should keep their arrows on the stiff side. This will minimize their chance of broadhead steering and maximize their close range accuracy. For open range hunters, they need to have a properly spined arrow and well tuned shooting system.


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