# Underspined Arrow Question



## bowhuntr311 (May 20, 2009)

So I bought a new Z7 this last week. 70lbs 30in draw with 29in arrows.
Easton Axis 400s and Beman ICS 400s with 100gr tips.

I've been shooting them both for years with out any issues out of a 67lb Outback, 65lb DXT. 
So Ive been shooting this new Z7 with the Axis 400s and I can see what looks like clockwise circles in the arrow flight. At 20yards Im getting 1 out 3 arrows that seems to be an inch or two off of where I "thought" it should of been. But its not always the same arrow.

I just got the bow and have only shot it about 45times at 20yards. The proshop paper tuned it and that has been it. No other tuning yet.

Im wondering if these flyers are becuase of shooting underspined arrows. The charts seem to call for 340s but I hoped the 400s would do the same job so I dont have to buy new arrows. I kinda assumed that the 400s out of the other mathews worked they would out of this bow.

Let me know what you guys think.


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## scclimber (May 2, 2007)

the 340 would definately do better with that setup. the z7 has a more aggressive cam than the outback or dxt you are shooting. with most of the new bows, i err on the stiff side. if you are getting odd results now, wait til you screw a broadhead on there.


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## ajstrider (Feb 20, 2009)

Yeah I think you are only going to amplify your problems once you start shooting broadheads. Shooting the 400 spine on your old bows was probably pushing it and now the new bows pack even more kinetic energy which make them even more dangerous to underspine. Your arrow will undergo even more stress and flexing if you put a fixed blade broadhead on there due to its increased resistance placed on the arrow from wind resistance. Once you hit about 62 to 63 pounds of draw weight you should start shooting the 340 spine in my opinion, especially if you have a 30" draw length.


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## konrad (Mar 29, 2009)

A "quick and dirty" test to verify weak spine would be to exchange those 100's for lighter points i.e. 75's.
If the groups improve, you have your answer.


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## Deezlin (Feb 5, 2004)

konrad said:


> A "quick and dirty" test to verify weak spine would be to exchange those 100's for lighter points i.e. 75's.
> If the groups improve, you have your answer.


I agree. I have had the same issue with arrows. Decreasing the point weight and/or bow draw weight will answer your question. I have been have the same problem with some Alpines.


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## b0w_bender (Apr 30, 2006)

Yup lighter points make a difference. 
Adding cresting wraps also increases spine.
Shorter arrows will also be stiffer.
Dropping the bow weight will allow you to test arrow spine. (requires sight adjustment though)

Also take a look at the rest and check for clearance issues. Spaying the rest area with foot powder before you shoot will highlight any areas your fetching maybe hitting since the foot powder will be scratched away on impact.


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## bowhuntr311 (May 20, 2009)

Is there a way to tell if a person has arrows that are too week of spine? Ex. Erratic arrow flight, inability to tune? Im going to try dropping the weight done to 60lbs to see if anything improves, seeings how its the cheapest. I can always pick up a few 340s if that doesnt help.


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## konrad (Mar 29, 2009)

I use Easton Technical’s web-site (shaft selector program) to play with the “what ifs?”
These folks are the undisputed industry leaders and have experienced virtually every bad thing that can affect accuracy.

Go to the link and plug in your numbers.

http://www.eastonarchery.com/products/selection

A chart will pop up that shows you which arrow will work with your bow draw weight, cam configuration, completed arrow length and point weight.
The program says 340 is the correct spine for your current set-up.

You can also drop your bow’s draw weight for experimentation; however, CAUTION contact your dealer to verify how many turns out you can go out on the limb bolts.


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## konrad (Mar 29, 2009)

Of course, there are other issues that can give the symptoms you are describing i.e. rest timing, rest position, vane contact, nock height, etc.
The place to start; however, is using the correct shaft for your application


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## TN.Frank (Sep 9, 2002)

Yep, lighter points would help to "stiffen" the spine a bit so you can tell what's what. If they shoot better with a lighter point then you'll either need to stay lighter or get a stiffer spine to shoot a 100gr tip.


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## KY-Z7 (Dec 21, 2009)

*Z7 spine*

I ran into a similar problem in January when I traded my SBXT in for my Z7.

I had been shooting Beman ICS Hunter 400's in my SBXT for several years without any issues.

With the Z7, the Bemans were grouping OK, but the arrow flight was terrible.

I downloaded the trial version of On Tap. It recommended somewhere around .320 spine for my draw length, poundage, and arrow weight. I can't remember the exact number and my trial version ran out.

I got some Victory HV V3's in .300 spine a couple of weeks ago. The arrow flight is perfect and the groups are great.

Both the Beman's and the Victory's are cut at 28.5 inches. I am using 100 grain tips.

Good luck.


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## bowhuntr311 (May 20, 2009)

So tonight a buddy and I decided we'd try to figure out a work around for having to buy 340 arrows.

I dug out a handful of Beman ICS 400s. They shot great, no erratic flyers, consistant arrow flight. 28.75inches with 100gr tips.

The Axis 400s 29in with 100gr tips were same thing as before. Random arrow flight, and you could see the tail kicking one way every once in the while.
Then I had one arrow splinter at the tip up about 9inches.:angry: I dont think I hurt any shafts with another to cuase it.

And I couldnt find any 75gr tips so I couldnt test that either. 

So now my questions are:

Could too much force on a week arrow be a cuase for the splintering and if so wouldnt it want splinter in the middle where the most flex would be?

Why do the Bemans seem to fly fine at 70lbs and at low 60s and the Axis dont fly well either way? Possible that bemans are just much better and/or stiffer even though both 400s?


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## bowhuntr311 (May 20, 2009)

Anybody?


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## konrad (Mar 29, 2009)

*wealthy cat*

Beeman is made by Easton Technical.

If the arrow is hitting the target in the middle of an oscillation, it is the same as flexing it between your hands.
I suspect the carbon matrix had already been damaged from an earlier event (i.e. hard contact with another arrow).

Easton strongly suggests “rolling and flexing” while listening for cracking sounds, running a soft cloth over the entire shaft length testing for splinters and twisting the shaft to see if it gives after EVERY shot to check for damage. 

One of my favorite things to read is “A carbon arrow is either straight or broken”. This is a totally wrong idea about carbon composite construction. An arrow can indeed still be straight and critically damaged. 

While the Beemans are apparently flying OK, the Easton web-site clearly says the 400’s are too weak. Current compound bow design always dictates erring to the heavy side when choosing shaft spine, not the light.

Hey, you already dropped a grand on the Z, what’s another couple of hundred bucks for an independently wealthy cat like you?


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## bulldog18 (Jan 20, 2006)

I just made some arrows for my friend with a z7 at 29/70. You need a .300 spine shaft. The problem is that the new z7 as well as the reezen have a extra hard cam on them. They are putting more energy into the arrow and with a weaker spine they can splinter. It is not worth the risk of shooting a weaker spined arrow to cause damage to your arm, bow and arrow.


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