# Spine Ratings



## 3-D Junkie (Sep 13, 2005)

In another thread there was some disscussion about spine as related to long range and short range accuracy. I have some input and questions about this subject. First off let me start by saying that I am no engineer, heck I didn't even graduate from high school, and I know there are people who will read this that have probably forgotten more about archery than I may ever know. But I am hoping to get some answers from people who really know this subject.

Now to start I want to define what spine is so those that don't understand can learn from this also. Shaft spine is: a shafts resistance to flex or deflection under a given load, when that load is, applied to an end of the shaft. 
And so we don't stray from the subject we will assume that all shots are taken indoors with no wind and from a hooter shooter to take out the nature and human error arguement for now.

Here are my thoughts and questions. 1) I believe that if you have a shaft that is spined "correctly", That for the most part any shaft with that same spine should shoot with a nearly identical degree of repeatability. Now when I say repeatability I mean that one arrow type will have a certain degree of group consistancy. and another arrow may be of a different weight or diameter, or made of a different material, so it will hit a different mark, but would still have nearly identical grouping.

I want to know if this is correct or not. And if not, WHY?


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## nuts&bolts (Mar 25, 2005)

*Spine rating for an arrow to match a bow and a shooter, not distance*



3-D Junkie said:


> Here are my thoughts and questions. 1) I believe that if you have a shaft that is spined "correctly", That for the most part any shaft with that same spine should shoot with a nearly identical degree of repeatability. Now when I say repeatability I mean that one arrow type will have a certain degree of group consistancy. and another arrow may be of a different weight or diameter, or made of a different material, so it will hit a different mark, but would still have nearly identical grouping.
> 
> I want to know if this is correct or not. And if not, WHY?


3D-Junkie:

You are absolutely correct. If you are using a Hooter Shooter, indoors, an arrow with the best match to a bow (draw weight and draw length) will shoot arrow after arrow into the same hole on the target. You may need to rotate the nock to find the best position to get a dozen arrows to hit the same hole (nock indexing). 

The correct arrow spine for a specific bow, set at a particular draw length, set at a particular draw weight, will be accurate at short distances, medium and long distances. You can use software programs (Archer's Advantage, TAP or OnTarget2!) to find the best spine rating for an arrow, as long as you tell the program which bow, what draw weight, what draw length, the model of arrow, the weight of the target tip or broadhead, the length of the shaft, insert or no insert, the brand of nock, and the brand of fletching.

It is a fact that you can manufacture aluminum tubes to be very straight and with a very consistent thickness. The Easton X7 aluminum arrows are very accurate, very popular and much cheaper in price compared to the top of the line Olympic arrows that are combination carbon/aluminum. The only downside to aluminum arrows are the weight, i.e, much heavier than a carbon arrow.

For indoor shooting at 20 yds, the weight of an aluminum arrow is not an issue. 

For outdoor FITA shooters trying to reach 100 yds with a recurve bow, weight becomes a very big issue. Very few FITA recurve shooters are using aluminum arrows. Most are using the combination aluminum/carbon arrows. The combo arrows must be spined to match the bow being used. Whether a FITA shooter is shooting 30 yds or 100 yds, he/she will use the same arrow because it matches that bow.


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## railbird (May 21, 2005)

The above reply comes from a knowledgeable archer and, just for grins, I will include a link to a very good article on the subject.

http://www.huntersfriend.com/arrowhelp/arrow-selection-3.htm


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## 3-D Junkie (Sep 13, 2005)

*Thank you nuts& bolts*

O.K. now that being established, I will continue.

If different shafts will demonstrate similar repeatability as long as the spine is equal, then isn't it safe to say that if you know your draw length, arrow length, draw weight, ect., that your first issue in choosing the correct arrow to use is matching the spine rating, rather than material, diameter, weight, wall thickness, or manufacturer. And if you agree with that, wouldn't you be better off choosing an arrow by compiling a list of the arrows that will have the correct spine rating at your given shaft length, and choose the arrow from that list that best matches the type of shooting you intend to use that shaft for.


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## nuts&bolts (Mar 25, 2005)

*Exactly, and that's what archery software will do for you*



3-D Junkie said:


> O.K. now that being established, I will continue.
> 
> If different shafts will demonstrate similar repeatability as long as the spine is equal, then isn't it safe to say that if you know your draw length, arrow length, draw weight, ect., that your first issue in choosing the correct arrow to use is matching the spine rating, rather than material, diameter, weight, wall thickness, or manufacturer. And if you agree with that, wouldn't you be better off choosing an arrow by compiling a list of the arrows that will have the correct spine rating at your given shaft length, and choose the arrow from that list that best matches the type of shooting you intend to use that shaft for.


3-D Junkie:

You nailed it exactly. 

TAP, OnTarget2! and Archer's Advantage does exactly what you just said. You plug in the brand and model of bow you have, the draw weight, your draw length, your preferred arrow shaft length, your preferred tip weight and the software will calculate the correct arrow spine. You can ask the software to give you a list of all arrows that fit your requirements. The software will even give you the estimated total weight of the finished arrow.

A lighter weight arrow with the correct spine will fly with a flatter trajectory. The heavier arrows with the correct spine will give a hunter more kinetic energy (knock-down power and pass through capability).


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## Jerry/NJ (Jan 17, 2003)

*Great thread!*

Guys, this is great information as spine is so misunderstood IMO. 

N&B's mentioned computer programs like TAP, etc. which IMO if you mess around with arrows, bows, etc. any amount, is well worth the cost. 
One of the things some may not be aware is a bow's efficiency or "performance factor" in TAP which also affects what arrow is needed. 
An example....my new Tribute bow. I weighed my arrow, shot it thru a chronograph and plugged the draw weight, draw length, the arrow weight, the speed, the axle to axle, and the brace height into the program and it calculates my performance factor, which was 1.3228. This is a high number and shows the bow is extremely efficient in regard to delivering the stored energy to that arrow. I shot a lighter weight arrow and got a 1.31 number so that showed the lighter arrow was not making my bow as efficient as it could be (the transfer of energy to the arrow). To give you an idea of a bow that is not efficient, it would have a performance factor of say for example; 1.100.
Now the reason I tell you this. Today's bows are very powerful and efficient and one bow may require a different spined arrow than another, yet the draw weight and draw length may be the same. You might be saying WTH Jerry?  

OK, an example......I am shooting my Tribute at 62#, 28.5" draw length (I wont even mention using smooth mods) and I am shooting my Mighty Mite at the same draw weight and draw length but yet, they require different spined arrows based on that performance factor. To add to the mix, I could have 2 bows exactly alike except one has a custom made string and this bow will have a higher performance factor than the other one and might require a stiffer spined arrow with all else being equal.
This is one reason I dont even bother to look at arrow companies charts as they are so vague and generic. They dont take all these things discussed into account, they can't without a program to do it like TAP,etc. 

I wrote this not to confuse anyone but to give an insight as to what all is involved in the mix concerning spine selection.


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## nuts&bolts (Mar 25, 2005)

*Solution, buy both TAP and OnTarget2!*



Jerry/NJ said:


> Guys, this is great information as spine is so misunderstood IMO.
> 
> N&B's mentioned computer programs like TAP, etc. which IMO if you mess around with arrows, bows, etc. any amount, is well worth the cost.
> 
> I wrote this not to confuse anyone but to give an insight as to what all is involved in the mix concerning spine selection.


Hi Jerry/NJ:

I solved that problem by buying both programs TAP and OnTarget2!:banana: 

Yup, what Jerry says. The Easton arrow selector gives not the best recommendations, and the charts from the arrow vendors are very approximate suggestions.

Use your favorite archery software, find the best combination of arrow length, tip weight, arrow wrap or not (fine tunes dynamic spine), and vanes/feathers, and then you will be very happy with the results.

Lots of fine bows these days. Each year, the mix gets more interesting. Having a poor match between arrow spine and your bow will have you pulling your hair out wondering "...is it me..." or "...is it the bow..."

nuts&bolts.


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## Iowa3dhunter (Sep 26, 2003)

What if none of the programs have my bow as an option?


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## 3-D Junkie (Sep 13, 2005)

Jerry/NJ this is, in my opinion, what archery talk is supposed to be about.
Now back to the issue, given that matching arrow spine is obviously a crucial factor in acheiving maximum performance from your bow, wouldn't it stand to reason that manufacturers of arrow shafts, and bows, make it easier for the average archer to realize the potential of the equipment they make. 
I don't believe that this would be a hard thing to do, and it would reduce negative feedback about good equipment. There has to be hundreds of people every year that buy a new bow of excellent quality, but the person belives the bow is crap because they are shooting an underspined or overspined shaft, and can't get any consistency from their setup. Or vise/versa, they have a bow that they know is good but buy a dozen arrows, at $175 or more and can't group nearly as well as they could with their old cheap arrows.

I see a way this can be addressed that would be easy to understand for the average consumer.
First, shaft manufacturers could make charts available for each shaft they manufacture that show the spine rating for that shaft at different lengths in 1/2 inch, or 1 inch increments. 
Second, bow manufacturers could give a proper spine recommendation chart for thier bows by draw weight in one pound increments, and draw length in 1/2 inch or 1 inch increments.

This way you could buy a new bow and once you have it set up to your liking, a lot of the guess work in finding the proper arrow is eliminated. We all know the the archery products industry is supported mainly by hunters, but the average hunter has no clue about what spine really is or how to choose the correct arrow for their rig. 

These are just my .02. Let me know what you think!


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## [email protected] (Feb 23, 2004)

>>What if none of the programs have my bow as an option?

OnTarget2! products have fairly complete databases for 2002 thru 2005 products and model years (bows, arrows, nocks, vanes, sights). 

2006 databases are in the works. 

If you find your bow is not listed, OnTarget2! products allow you enter your bow data and save it in a custom user record. Collecting the data usually isn't a problem, because most companies publish what is required on their websites. 

If you have a really old bow, then you'll have to get out your tape measure and have access to a chronograph. In lieu of a chronograph, and if you're using Software For Archers or Tapes And Charts, you'll need a couple of good sight marks and let the program calculate your velocity.


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## nuts&bolts (Mar 25, 2005)

*OnTarget is a great piece of software*

3-D Junkie:

OnTarget has all the information you are looking for. The software is easy to use and you can plug in hundreds of combinations of arrow lengths, any brand you like, all imaginable combinations of field points, target points, broadheads, arrow wrap or no arrow wrap, all brands and sizes of vanes or feathers, or you can ask the software to find the optimum arrow model for your specified bow, draw weight and draw length.

The bow manufacturers and arrow manufacturers will not publish free charts with the degree of specificity you described any time soon. Fortunately, the archery software vendors have taken the time to do it for us in a user friendly format.


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## Spotshooter2 (Oct 23, 2003)

3-D Junkie, the standard is already set to figure spine using a 2 pound (I believe) weight in the center span of 26 inches. THis is the industry standard


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## Steel Magnolia (Jan 2, 2005)

*Spine ratings*

Only one company that I know of will publish their spine tolerances. That is Carbon Tech. I shoot CT arrows exclusively and I can tell you that each batch is a matched set with +-.005 spine tolerance amongst them. The CT Hippo's are just the finest fat shaft and the CT Cheetah's are definately the fastest and most accurate. Just my .02 cents.

Steel Mag


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## 3-D Junkie (Sep 13, 2005)

Sharpshooter, I know Easton publishes these numbers but the rating you are talking about is a static spine rating and is not the same as dynamic spine.
I believe that a dynamic spine rating is what would be more beneficial to archers.
There is a link to an article on this subject, posted by railbird earlier in this thread. This is good info and I suggest anyone who doesn't understand the difference to read it.

NUTS & BOLTS, I really appreciate your input on this subject, I am going to look into this software and will most likely get it. I just wish manufacturers would take the time to publish this info. I just don't believe that most archers, especially those that use there equipment for hunting, and don't compete, will spend the money to get this software. In fact most probably don't even know it exists. And even though most of us here on AT eat, sleep, and breath archery, those that don't should still be able to make the most of their equipment.


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## Black Snowman (Dec 26, 2005)

Easton makes an effort. They have a free software that lets you plug in the numbers and get an approximation. But there are many archers out there that don't have internet access, or don't want to do the kind of research we do.

They are dependant on their local archery shops to do the homework for them and pay for it, usually in cash.  Hopefully the people in the shops actually know what they are taking about and have invested in the proper tools and done the research. From several of the posts here I get the impression that this isn't always the case.

This is why I work on all my own stuff. Cars, motorcycle, guns, and now bow. I'd rather learn it and know it so I know it's done right and can spot it when it's not. It's a lot of work, but I enjoy it, it saves me money, and it gives me piece of mind.

Everyone not willing to do so just needs to remember "Buyer beware."


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## chrstphr (Nov 23, 2005)

[email protected] said:


> >>What if none of the programs have my bow as an option?
> 
> OnTarget2! products have fairly complete databases for 2002 thru 2005 products and model years (bows, arrows, nocks, vanes, sights).
> 
> ...


actually i tried ontarget and i think archers advantage. both software did not have my bow listed. I am a minority olympic recurce shooter and my hoyt aerotec was not a bow choice. All the hoyts listed to choose from are compound. i have yet to find a software that i can use. In fact i had trouble getting most of the software to let me blank out the cam settings and compound settings to get any kind of reading. I realise that i am way in the minority shooting recurve but found that statement to be quite true about the software not having my 2004 hoyt aerotec. For compound shooters i can see how awesome the software is, but not recurve.


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## nuts&bolts (Mar 25, 2005)

*OnTarget has a recurve setting*



chrstphr said:


> actually i tried ontarget and i think archers advantage. both software did not have my bow listed. I am a minority olympic recurce shooter and my hoyt aerotec was not a bow choice. All the hoyts listed to choose from are compound. i have yet to find a software that i can use. In fact i had trouble getting most of the software to let me blank out the cam settings and compound settings to get any kind of reading. I realise that i am way in the minority shooting recurve but found that statement to be quite true about the software not having my 2004 hoyt aerotec. For compound shooters i can see how awesome the software is, but not recurve.


chrstphr:

OnTarget does not have a listing for a specific recurve bow, because the force draw curve is a function of the limbs, and not the riser.

Plug in the arrow shaft model, brand of nock, brand of sight in OnTarget. 

Goto the spine match page, and under the "cam" button, pick "recurve" on the scroll down menu. 

Under ATA, plug in 66 for short limbs, 68 for medium limbs or 70 for long limbs if you are using the 25-inch Aerotech riser.

Plug in your draw length and draw weight on the fingers.

Now, you can play with different arrows (carbon or aluminum), play with tip weights, wrap or no wrap (plug in as additional weight at nock end), etc.

OnTarget actually works quite well for recurve. TAP also has a recurve setting as well.


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## [email protected] (Feb 23, 2004)

Chris,

With OnTarget!, do the following to "create" a recurve...

On The Equipment tab..

In the Bow Specs frame...
1) select "Recurve" from the Cam Style combo box.
2) set Overdraw Length to 0.0
3) set Axle to Axle to your bow length...66.0, 68.0, 70.0, etc.
4) enter your brace height, draw weight, and draw length.

In the Weight On String frame...
1) enter 0 in the Peep and D-Loop fields (assuming FITA style)
2) probably 3 or 4 for Nock Point, if using a tied-on nockpoint.
3) uncheck the Release Aid check box (assumes fingers).

In the Performance frame...
You'll have to fudge the IBO velocity. You probably already have a general idea of how fast your bow is with the arrow you're using. Just change the IBO velocity until the program's Calculated Velocity agrees with your "known velocity".

Save the stuff you've entered in a custom user record file...so you don't have to re-enter it. Reload the same user record file again when you start the program.

Instant (well almost) recurve! 

Data entered on the Equipment tab will automatically be transfered to the other program tabs when you click to them...like the Spine Match tab.


LOL...nuts&bolts types faster than I do.


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## Spotshooter2 (Oct 23, 2003)

I dont know if any companies do a dynamic spine test since that would have to be done on an arrow that is shot. I think you are over thinking the whole issue of spine.


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## blue thunder (Jan 20, 2003)

Thank you guys.I have just purchased the On Target 2 and you have provided me with a ton of information about the program.As was said earlier,this is one of the best threads I've read since I came to AT.


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## nuts&bolts (Mar 25, 2005)

*Great program*



blue thunder said:


> Thank you guys.I have just purchased the On Target 2 and you have provided me with a ton of information about the program.As was said earlier,this is one of the best threads I've read since I came to AT.


You're going to have a lot of fun with OnTarget2. I was a little apprehensive in the beginning, but once you get the hang of it, you will find that it's a lot of fun working out all the different combinations to try to fine tune this or that.


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## KYShooter (Jun 23, 2004)

Nuts- I noticed above you mentioned using both TAP and OnTarget. What advantage is there to using both programs? I have TAP, and am familliar with it, great program, Ive looked at OnTarget, and it looks very nice also, but what is the advantage to having both?


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## nuts&bolts (Mar 25, 2005)

*No real advantage, both are great programs*



KYShooter said:


> Nuts- I noticed above you mentioned using both TAP and OnTarget. What advantage is there to using both programs? I have TAP, and am familliar with it, great program, Ive looked at OnTarget, and it looks very nice also, but what is the advantage to having both?


KYShooter:

I bought TAP first. Was waiting for the unlock code. Got impatient, and bought ONTarget2 on a whim. OnTarget2 was a little harder for me to figure out how to use, so started using TAP. TAP is Very intuitive, pretty easy to figure out. 

I saw great reviews from AKDoug for OnTarget2, whom I respect very much, so I tried to teach myself OnTarget2. I like OnTarget more and now use it most often. 

One difference between the two programs. TAP does assume the arrow length to be end of shaft to end of nock groove. OnTarget assumes the arrow shaft length to be the length of shaft only, not including the nock distance.

If you are ever interested, Pinwheel does offer a free trial.


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## Black Snowman (Dec 26, 2005)

*Another thumbs up for OnTarget2!*

Even though it didn't include my bow (Cabela's PL-1.5) my sight (because it can't be marked) or the arrows I had chronographed through it (Beman Mirage 7032s) I still bought the OnTarget2! SFA because it was so powerful and informative, and I know this won't be my last bow or set of arrows.

I found it a little confusing at first but I was able to figure it out without the instructions. I'm sure I'm missing out on some things so I'm going to go back and eek some more details from help file. It will take a little time but I'll be able to get the most from it.

I had already ordered new arrows (Super Carbon Magnum 55/70s) so I decided to see if I needed to make any adjustments to the setup. I plugged in all of the info. I thought I was going to need more FOC and get a heavier point but it turns out the configuration I'll be getting has the perfect dynamic spine for my bow's setup and the 100 gr points I had chosen. So, that makes me think I should look into using a mechanical broadhead with this particular arrow if I decided to use it for hunting.

It also told me I have energy to spare out at 60 yards that I could trust a mechanical to do it's job, even with such a light arrow. So it just saved me several sets of arrows and hours of experimentation and even gave me information I couldn't estimate on my own. Well worth the $25 to me.


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## 3-D Junkie (Sep 13, 2005)

Spotshooter2 said:


> I dont know if any companies do a dynamic spine test since that would have to be done on an arrow that is shot. I think you are over thinking the whole issue of spine.


 I dont think that it would have to be done on an arrow that is shot. I don't know if such a mchine exists but one could be made to measure dynamic spine. Instead of hanging a weight on the center of a horizontal shaft, momentary pressure could be applied to one end of a shaft and a given amount of resistence to the other and the deflection could be measured.
I know some may think that this is crazy talk, but its not that hard of a thing IMO to measure. Is it possible to overthink this? I say no. Manufacturers spend millions each year developing this great equipment, thats better, smoother or faster than last years stuff. It does not matter how much energy your bow can put out if it can't do it with repeatability. You will just miss faster. I believe that the first bow and shaft manufacturers who make this information accssible will gain a major market share over those that don't.


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## [email protected] (Feb 23, 2004)

Black Snowman,

Sorry I missed that one. :embara: The Cabela's bows (PL-1 & PL1.5) will be in the next database release.


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## Spotshooter2 (Oct 23, 2003)

DYNAMIC SPINE is how much the arrow does bend when fired. This depends upon stiffness (Static Spine), string force, fletching, nock weights, etc.) "Weak" and "Stiffness" are often used in terms of Dynamic Spine. 

It is more difficult to determine Dynamic Spine than Static Spine because all the simple formulas don't work with such a massive force acting down the shaft. Consulting a Machinery's Handbook or other Engineering manual will give beam formulas to determine Static Spine, but when dealing with a large compressive force, "all bets are off."

Here is the definition for Dynamic spine. your momentary pressure will not work to test this because how much pressure do you put on it . Also when shot the arrow is put through varying degrees of momentum as the string advances. Also on an arrow that is shot dynamic spine is affected by tip weight and to other degrees arrow fletching , nock , arrow wraps. Me I am just going to get the arrows that are suited for my setup and go and shoot them and not worry about dynamic spine.


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## XMAN (Jul 2, 2003)

N&B: What about On Target 2 verses Archer's Advantage?
Mike


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## hoggin03 (Oct 24, 2005)

nuts&bolts said:


> If you are ever interested, Pinwheel does offer a free trial.


Where can you download the free trial? I'd like to see the software in action.

*****Scratch that - I figured it out!*****


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## nuts&bolts (Mar 25, 2005)

*Haven't tried AA, but I do own TAP and OnTarget 2!*



XMAN said:


> N&B: What about On Target 2 verses Archer's Advantage?
> Mike


I haven't tried AA. I own TAP and OnTarget2!

TAP is very intuitive and easy to learn. OnTarget2! has a fuller interface, but once you get the hang of it, pretty easy to use. Lately, I use OnTarget2! exclusively.


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## hoggin03 (Oct 24, 2005)

Maybe one of you guys could help me out when you have a minute?

I downloaded the trial version of the spine selector. I punched in some info to see what it suggests for arrows. Could someone with more experience than me try this to confirm what it is telling me? Here's my info.

Switchback XT
Hunting usage
Carbon arrows only
31" AtoA
7.75 brace height
70 pounds
29"
27.5" arrow
peep sight
string loop
NO brass nocking points
release
100 grain 3-blade broadhead

Thanks for the help!!!


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## nuts&bolts (Mar 25, 2005)

*You should be looking for something in the 0.360 spine range*



hoggin03 said:


> Maybe one of you guys could help me out when you have a minute?
> 
> I downloaded the trial version of the spine selector. I punched in some info to see what it suggests for arrows. Could someone with more experience than me try this to confirm what it is telling me? Here's my info.
> 
> ...


hoggin03:

You should be looking for something in the 0.360 spine range.

I would suggest the Easton Axis 340s where end of shaft to end of nock groove is 29-inches. If you cut Axis 340s at 27.5 inches, the 100 grain broadhead is not heavy enough, and the shaft would be too stiff.

Another suggestion would be the GoldTip XT Hunter 7595 where end of shaft to end of nock groove is 29-inches. If you cut GT 7595 at 27.5 inches, the 100 grain broadhead is not heavy enough, and the shaft would also be too stiff.


Both of these shafts give you approximately 10% FOC balance.

I prefer to go with 12-15% FOC balance, but you would need to purchase heavier broadheads, and a shorter arrow.


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## hoggin03 (Oct 24, 2005)

nuts&bolts said:


> hoggin03:
> 
> You should be looking for something in the 0.360 spine range.
> 
> ...


Thanks a lot, nuts&bolts! I really appreciate your help.


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