# Arrow spine size?



## #1DEER 1-I (Sep 10, 2007)

Just wondering about spine size. Ive bow hunted for years and not made much sense of what difference the arrow spine size makes. What difference does the spine size make? And what spine sizes do you guys use?


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## bow_dude (Aug 20, 2009)

Spine size is determined by your draw length and bow draw weight. If the spine is too weak, you stand a chance of the arrow breaking on the release and being driven into your arm. With the correct spine, you will see improved accuracy and shrinking of your groups. I am of the group that believes you can under spine but not over spine unless you are shooting a stick bow where arrow paradox comes into play. What is your draw weight and length and then we can give you some parameters to work with. Also, are you shooting stick or compound. You also have to factor in tip weight and if you are shooting fingers or releases. Most arrow charts don't factor in what's on the string, type of release and tip weight. I have found most charts under spine and aren't as accurate as they need to be. I went to a computer aided spine chart years ago and by so doing saw improved accuracy and shrinking of groups.

In answer to your question of spine, I am shooting a 300 spine and a 350 spine with my 70 lb bow with a 27.5" shaft. I am shooting a 400 spine with the same draw but 60 lb bow. The 350 is border line depending upon the tip weight for the 70 lb bow.


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## #1DEER 1-I (Sep 10, 2007)

I shoot a 60-70# bow with a 28" draw length.


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## Fowlmouth (Oct 4, 2008)

I shoot 400's... 28" shaft length at 60 pounds. 100 grain fieldpoints/broadheads.


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## kdog (May 4, 2015)

#1DEER 1-I said:


> I shoot a 60-70# bow with a 28" draw length.


if you are shooting 100-125 grain tips I would stay 350 and up with the arrow cut to 27- 28 inches or so. at 70 that may be pushing it, below 70 and you are fine. that is my best guess, an arrow spine program will get more specific.

I can't shoot less than 350 with a 100 grain tip, and am shooting at 67 pounds, but I am a 30 inch draw. with a 28 inch draw you likely have a bit more flexibility.


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## TPrawitt91 (Sep 1, 2015)

I'm shooting 300's with a 31" draw and 65# draw. Pretty certain 100 grain tips.


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## alpinebowman (Sep 24, 2007)

this is a little misleading. Spine is determined by the amount an arrow flexes over a 28" span with a 2lb weight in the center of the span. the 350 signifies the .350" the arrow bent at that weight. Bow dudes comments are more to find teh correct spine needed for your setup.
And to chime in on mine I also use a 26" 350 arrow at a 27.5" draw with a 132 grains up front on a 62lb speed bow. I have shot a stiff 350 spine for a lot of years with great results.



bow_dude said:


> Spine size is determined by your draw length and bow draw weight. If the spine is too weak, you stand a chance of the arrow breaking on the release and being driven into your arm. With the correct spine, you will see improved accuracy and shrinking of your groups. I am of the group that believes you can under spine but not over spine unless you are shooting a stick bow where arrow paradox comes into play. What is your draw weight and length and then we can give you some parameters to work with. Also, are you shooting stick or compound. You also have to factor in tip weight and if you are shooting fingers or releases. Most arrow charts don't factor in what's on the string, type of release and tip weight. I have found most charts under spine and aren't as accurate as they need to be. I went to a computer aided spine chart years ago and by so doing saw improved accuracy and shrinking of groups.
> 
> In answer to your question of spine, I am shooting a 300 spine and a 350 spine with my 70 lb bow with a 27.5" shaft. I am shooting a 400 spine with the same draw but 60 lb bow. The 350 is border line depending upon the tip weight for the 70 lb bow.


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## alpinebowman (Sep 24, 2007)

This is my old setup to a T and I have shot a 26-27" 350 spine arrow with great results. The only exception would be if you are shooting a speed bow at 70lbs you may want to run the 300 spine in it.


#1DEER 1-I said:


> I shoot a 60-70# bow with a 28" draw length.


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## RemingtonCountry (Feb 17, 2016)

31.5 inch draw, 72 lbs draw weight.

Decent accuracy with 340's in the past, but made the jump to 300's and saw my accuracy improve immensely!


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## alpinebowman (Sep 24, 2007)

I would imagine. I would venture to guess you really need to be shooting 250's with that draw length so a 340 would be really weak.


RemingtonCountry said:


> 31.5 inch draw, 72 lbs draw weight.
> 
> Decent accuracy with 340's in the past, but made the jump to 300's and saw my accuracy improve immensely!


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## RemingtonCountry (Feb 17, 2016)

Definitely, I was shooting the 340's when I was at 60 lbs. I actually have some 250's on their way to see if there in an improvement from the 300's.


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## alpinebowman (Sep 24, 2007)

I imagine they will. I have a friend shooting a 31" draw and at 70lbs with a 29" 250 arrow he is right on to a little weak with it.


RemingtonCountry said:


> Definitely, I was shooting the 340's when I was at 60 lbs. I actually have some 250's on their way to see if there in an improvement from the 300's.


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## bow_dude (Aug 20, 2009)

#1 Deer... still need more information. 60-70 lbs is too vague. Also, need to know the tip weight and what is on the string, (peep, d-loop, brass nock set, kisser button). As well as compound or stick bow and if a compound, type of cam. All this makes a difference in determining the correct spine for your setup.


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## mrkrik (Jan 26, 2016)

I've used OnTarget2 archery software for years to figure out my arrow set up. It seems to work really well as I've always ended up with an arrow that shoots really well. It allows you to change every variable and see how it affects the arrow. It also allows you to print sight tapes and run shot simulations. It takes a little to learn how to use it, but once you do, it's quick and simple. When I buy shafts and build my arrows, I always run it through the program first to decide what to order. A great archery tool.


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## RandomElk16 (Sep 17, 2013)

I am late to the party, and not a long time bowhunter but have dove into it quite a bit...

I started with a 400 spine on a 27.5" draw at 65#. I bumped up to 70# and was told I could stay the same. I noticed my groups got a bit worse so I did some of my own reading... I headed back to the bow shop and asked about a stiffer spine and was told that I should make the switch (this guy clearly more knowledgeable than the last). I know that the draw length and weight is what all the charts show... again, I am an amateur but I can't imagine speed doesn't factor into that. My bow shoots pretty fast..

I moved up to the 340, and all I can say is I am happy I did. My groupings got tighter and I just "feel" like the arrow flies so much nicer. I imagine going to a 250 or a 200 I might feel "overspined" but, after my experiences I would tilt to the heavier spine. In the spring I even reduced draw weight to 65 on a new bow for some experimenting and the 340 still felt better than the 400.


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## High Desert Elk (Aug 21, 2012)

I have shot 400 FMJ's from a 70# w/29" draw cut to 28" with 125 up front just fine. I wonder how much of a safety factor is built into the mechanics of arrows today. A lot I'm sure...

No doubt, a lot of weight up front with a "flimsy" arrow being shot fast can have its consequences. However, a heavy arrow with minimal FOC to absorb more of the bows energy to get it moving matters most. It won't flex the same as a higher FOC. If shooting a lighter arrow, defiantly go with a stiffer spine. If shooting for more FOC, go with a stiffer spine.


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## KineKilla (Jan 28, 2011)

Thread resurrection....

As I am new to archery and am working my way up in draw weight, have any of you used a spine that is the next level stiffer in anticipation of being at that draw weight in the future?

I am currently at a 28.5" draw length, 50# (ish) draw weight shooting 5mm FMJ's with 400 Spine and 100gr tips. My arrows are cut a bit long. I'd guess my arrows are at 29" cut length which is what I asked for since I didn't want that broad head anywhere near my bow hand.

But I digress.....

Most charts put me at a 400-340 spine and anywhere in between. Definitely at a 340 once I get above 55# draw weight (which will be fairly soon if my elbow pain allows it). 

So is it going to be a big negative to start shooting the 340 spine arrows before I get to 55# ? Pros and Cons?


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## middlefork (Nov 2, 2008)

IMO over spined does not create problems. Under spinded will.


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