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Discussion Starter #1
I have heard people on AT say that changing the head weight on an arrow will change the spine. Why is that? The shaft didnt change. Is it the compession multiplying on the walls due to the exess head weight? Eastons charts don't list a difference for 100 to 125 heads. Whats up with this?:confused
 

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The important thing about arrow spine is how the arrow bends at launch. Certain situations, like finger release, benefit greatly when the arrow bends just right. Finger release causes the string to take a curvy path, so the arrow literally has to bend around the rest on its way out.

The force that actually causes the arrow to bend is compression due to its inertia (objects at rest want to stay at rest). The string lurches forward, pushing the nock end, but the point end of the arrow wants to stay put. So the arrow bends.

If you have two arrows with the same stiffness as measured on a stationary gage, they will have the same spine (deflection with a 2# weight suspended at mid span of 28", or something like that). If one arrow is heavy aluminum, and the other is much lighter carbon, the two will bend differently during launch. The lightweight carbon arrow will have much less mass to overcome, and will therefore bend less. The relatively heavy aluminum will bend more, because of the difficulty in getting all that mass moving.

A heavy point does the same thing. If you have an arrow with a 90 grain point that is giving you "stiff arrow" probems, you can increase the point weight and cause it to bend more at launch. This makes the arrow act as though it had a weaker spine, even though a static (unmoving) test will measure the same spine as before.

There are all kinds of things in archery that are measured with no motion, even though the dynamic situation is the one that matters. It is just too difficult to measure things as they accelerate 1/4 the speed of sound over less than 2 feet.

Scott
 

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Discussion Starter #3
Beezaur, Thank you. I do shoot fingers at 72#, 30" draw, dual cam. I am shooting 2514's with 100 gr points. They group well, but....the farther out I shoot, the farther to the left they fly. Never bothered me hunting, wasn't till I started competing that I noticed it. They are 29 and 3/4" long. TY for your reply.:) PS I have shot the same with Beman ICS hunter 300's and they too go left, same length. Is it my spine or my head weight or my rest, or what. Appreciate the help. TY! Bow is tuned good too, by the way.:confused:
 

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This might not be the most scientific, but here goes. Take a good length of conduit. A little flexible right? Shake one end up and down. The opposite end will flex a little okay? Now tape weld, or otherwise attach a weight of several ounces(results will vary depending on the weight and length of conduit). Now, with the weight on the opposite end on the conduit, wiggle your end around. The conduit will probably flex more and take longer to recover.

A possibly better, but similar example is a good graphite fishing rod. Take a good rod by itself. Give the handle a good snap(as if casting) with your wrist, but then stop it short quickly(an action similar to knocking on a door where your hand starts and stops quickly). The tip will bend a little from the inertia, but snap back into position right away. Now, tie a sinker or heavier lure to the end of the rod and give the handle another sharp snap. The rod will flex/bow more, and take longer to "recover." Correct? It seems to take less effort to make the rod or conduit flex with the extra weight on the end doesn't it? Does is seem like the "spine" of the conduit or fishing rod is what we might call weakened?

Hopefully that's clear enough to get the right idea.

peashooter
 

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Hollowpoint, I just read your last response. Are the arrows that are flying left broadhead tipped or fieldpoint tipped? Your bow may be tuned pretty well, but shooting at extended ranges can show very minor tuning errors-ones that would never show at close range. It's even possible that your sights are just slightly off. If you're off by a 1/4" at 20 yards, you could be shooting to the left quite a lot at some extended ranges you might be competing at.

Those 2514's are pretty stiff shafts, but you're proably putting out some pretty good power with 72 pounds at 30 inches. I would try tweaking the rest very slightly, or maybe making sure the sights are perfectly set up.

One thing I just though of. If you're using a multiple pin sight where all the pins have the same gang windage adjustment, some pins could be off. I've used a multi pin sight where I had to be careful when tightening down the pins. They were plastic, and if I cranked one much different than the other it would flex, and cause windage problems. Not sure if this applies to you or not.
Good luck.

peashooter
 

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Discussion Starter #6
Peashooter, TY for the response.:) I do not use sights. They go left with field, as well as broad heads. I have just recently caught myself holding to the right to make up for the drift. I have not shot the broadheads at a distance of more than 40 yds. (i wont hunting either), but they do group with the field points. I am currently shooting with a center rest flipper. I use 5" helical feathers. The bow in is a 02 pro-tec with 3000limbs. 240'ish FPS with theses arrows(if that makes a difference). Did not have this with my old 2 cam PSE, set up similarly.:confused: :confused: TY for any suggestions.:) GREAT FORUM!
 

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If you shoot barebow how do you know the arrow didn't go where it was pointed?
 

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Have you condsidered purchaseing Archers Advantages software, which has an arrow selection program, which is simply amazing. (Perry would agree!)
In fact, with the program, you can use a draw board and enter YOUR bows power stroke into the data base, and it will tell you which arrows from all companies are properly spined for you. It is not perfect, but better than anything out there. You can even input different tip weights and the program will tell you how that chnages spine.
With the 3000 limbs, I would guess that the 2514's are overspined. 2512 may be a better arrow for that set-up???? There is a group of archers out there that prefers to shoot arrows which are slightly underspined. I am in that camp. Good Luck!!
 

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Discussion Starter #9
Cambow, thank you. I went to my pro shop today and they put my set up in their computer. I am not shure if it was Archers Adavantage or not. Anyway, you were right on the money with the 2514's being too stiff for the limbs. With my set up they recomended 2512's with a 100 gr tip. He also said that with 125's on the 2514's it would help. I have tons of field and BH's in 100gr, so I got them fletching up some new shafts for me. FOC is improved with the 2512's also. My FOC was below 9% with my old setup. Thank You for the info!:) :) :) Shoot Strait>>------->
 

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Discussion Starter #10
Ian said:
If you shoot barebow how do you know the arrow didn't go where it was pointed?
Ian, after 13 yrs of shooting hundreds of arrows a week this way, I DO know how to aim. You don't NEED sights to tell you if something is not tuned properly. To answer your question, Left and right I line up with the arrow. If center shot is set up properly it should not go to one side or the other. (Unless yor spine is wrong). Elevation, I shoot the gap between where the arrow tip is and where I want it to hit. Examle, at 30yds the point of impact is 4" above where my eyes see the tip pointing at full draw. At 20 it is farther above. 34yds, it is dead on.:D It is really quite effective. :) Shoot Strait, no matter the method.:p
 

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A few grains of point weight does next to nothing for changing dynamic spine out of most compound/ release setups - IMO
Shaft length is a much more viable means to alter reaction.
Just dont do like me, I cut some twice and they are still too short:rolleyes:

Sean
 
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