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Discussion Starter #1
Can shooting an underspined arrow hurt your bow?

I realize 340 spine out of an RPM 360 70lb draw and 29" DL is underspined, according to charts. I've heard from other shooters, though, that sometimes an underspined arrow still shoots accurately. Would I be hurting anything to try my 31" 340 spine (100 grain point) to see if they will group decently? My primary concern is damage to the bow. If there is no possible bad outcome other than bad accuracy I'll give it a try.
 

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No, you’ll be more than safe. I’ve found most of my bows especially target bows, like a softer spine. Some people will tell you otherwise, but it won’t hurt to try
 

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Don't shoot an arrow that takes you under 5 grains per pound of draw weight. For example, if your bow is set to 60lbs., don't shoot an arrow that is less than 300 grains.
 

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I use 340 spine arrow in my Reign 6, 68.7# and 28.5" DL without problems.
Maybe 300 would be better for U, depending on length of arrow and FOC.

Actually if U try underspined arrow there's no real reason for it 'cause there's speed enough for 5.2Gr/pound arrow.
U get over 320fps speed and it's not actually necessary and are those arrows stabile anymore ?

Did take IRL speeds out from this:
https://youtu.be/z1mfGgnxsQM

If U put 380Gr arrow 5.4Gr/pound into it and it should go 319fps.
 

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I use 340 spine arrow in my Reign 6, 68.7# and 28.5" DL without problems.
Maybe 300 would be better for U, depending on length of arrow and FOC.

Actually if U try underspined arrow there's no real reason for it 'cause there's speed enough for 5.2Gr/pound arrow.
U get over 320fps speed and it's not actually necessary and are those arrows stabile anymore ?

Did take IRL speeds out from this:
https://youtu.be/z1mfGgnxsQM

If U put 380Gr arrow 5.4Gr/pound into it and it should go 319fps.
His question had nothing to do with speed in any way. It was actually a very simple question, will it hurt his bow, the answer is no it won't.
 

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To answer you question, No your bow wont be hurt.
 

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Can shooting an underspined arrow hurt your bow?

I realize 340 spine out of an RPM 360 70lb draw and 29" DL is underspined, according to charts. I've heard from other shooters, though, that sometimes an underspined arrow still shoots accurately. Would I be hurting anything to try my 31" 340 spine (100 grain point) to see if they will group decently? My primary concern is damage to the bow. If there is no possible bad outcome other than bad accuracy I'll give it a try.
With today's bows it doesn't really matter but back in the day, slightly weak was actually easier to tune. Some still side with that. As mentioned, the only true limit is going below manufacturer gpp spec which is 5gpp. Underspined doesn't mean the arrow will break it means the shaft will flex more. If it flexes too much you'll have a hard time tuning but that's it.
 

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An easy way to tell if your arrow spine is optimum is to shoot at the longest distance you are accurate at and adjust the bow weight by turning the limb bolts one turn at a time and see if there is a difference in accuracy. If you get more accurate at lower poundage than you know that you need to cut the arrow down or move up in spine. John Dudley teaches this method and calls it the HIL (horizontal impact line) method. When your arrow spine is correct your groups will shrink horizontally. It is a very simple and cheap way to find the best spine for you. I know you didn't ask for all this in your original question but I would suggest that trying the HIL tuning method would be your next step to find the right spine.
 

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Discussion Starter #9
An easy way to tell if your arrow spine is optimum is to shoot at the longest distance you are accurate at and adjust the bow weight by turning the limb bolts one turn at a time and see if there is a difference in accuracy. If you get more accurate at lower poundage than you know that you need to cut the arrow down or move up in spine. John Dudley teaches this method and calls it the HIL (horizontal impact line) method. When your arrow spine is correct your groups will shrink horizontally. It is a very simple and cheap way to find the best spine for you. I know you didn't ask for all this in your original question but I would suggest that trying the HIL tuning method would be your next step to find the right spine.
I didn't ask for it, but I'm glad you gave the information!
 

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Discussion Starter #10
Additional question:

Just double checked my arrow length, and they are 30 inches, instead of 31 like I thought. This puts me at about 342 grains of weight (8.1 gpi), with just shaft and tip. Will the total with fletchings, insert, and nock be enough to make the arrow safe for 70lb draw? The insert and nock are nothing special; just the typical aluminum insert and plastic nock. The vanes are Blazers.
 

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Additional question:

Just double checked my arrow length, and they are 30 inches, instead of 31 like I thought. This puts me at about 342 grains of weight (8.1 gpi), with just shaft and tip. Will the total with fletchings, insert, and nock be enough to make the arrow safe for 70lb draw? The insert and nock are nothing special; just the typical aluminum insert and plastic nock. The vanes are Blazers.
GPI is the weight of the bare shaft per inch and GPP is grains per inch of draw(weight). So 342/70=4.88 call it 5.
 

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Fleching, and nock will add about 25 grains. I don't know how heavy your insert is but your arrow will be heavy enough to meet the manufacturer recommended weight of 5 grains per pound of draw weight. 70×5=350 grains
 

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With a 29" DL, 70# DW, 31" arrow length, 360 IBO, even with a 100 grain point will be way underspined and probably unsafe.
 

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Unsafe, no it won't be!!!!!!! Not even close.
Yes, a 340 spine 31" long could be unsafe to shoot from his setup. First it is way underspined…..another reason is because arrow spine consistency is not perfect.....another reason is when shooting groups and an arrow hit/slap against another arrow, a underspined arrow is more likely to be damaged....It's always better for arrow spine to be a little on the stiff side. A little Common Sense goes a long way.


The chart below shows he would need a 250 spine at 65-70# and most of these charts are based on Bows around 330 IBO.

Arrow Spine Chart.....http://www.blackeaglearrows.com/arrowsizingchart-a/254.htm
 

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Yes, it could be unsafe to shoot from his setup. First it is way underspined…..another reason is because arrow spine consistency is not perfect.....another reason is when shooting groups and an arrow hit/slap against another an underspined arrow is more likely to be damaged....It's always better for arrow spine to be a little on the stiff side. A little Common Sense goes a long way.


The chart below shows he would need a 250 spine at 65-70# and most of these charts are based on Bows around 330 IBO.

Arrow Spine Chart.....http://www.blackeaglearrows.com/arrowsizingchart-a/254.htm
That's just misinformation. Shooting an underspined arrow is absolutely not unsafe. Heck I've shot 500 spine at 70 with 200gr on the front. And no it's just because I've done it, it's because arrow spine and arrow strength/safety are not dependant on each other. The safety concerns come up when the integrity starts to breakdown like when there's a crack in the carbon or bend in the aluminum.
 

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That's just misinformation. Shooting an underspined arrow is absolutely not unsafe. Heck I've shot 500 spine at 70 with 200gr on the front. And no it's just because I've done it, it's because arrow spine and arrow strength/safety are not dependant on each other. The safety concerns come up when the integrity starts to breakdown like when there's a crack in the carbon or bend in the aluminum.
Everyone has their opinion....I consider your post just misinformation. JMO
 

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Everyone has their opinion....I consider your post just misinformation. JMO
He’s only a bit weak, in no way unsafe.

If you use a target chart instead of a hunting chart he is actually considered good although still on the weaker side.

Arrows don’t start breaking because you put 50grains more tip wait on, and that is basically the equivalent of this set up.


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Actually he is correct. Not unsafe, just not the correct arrow. Damaged arrows are the ones that are unsafe.
An underspined arrow is more likely to be damaged when shooting groups, which is one reason why I consider then unsafe.
 
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