I have been fiddlefarting around with a bunch of different arrows to shoot out of my Kanga longbow. The bow is 55#s at 28". I started out with 2016s at 30 inches with a 125gr head. I have tried 2117s 2217s XX75s in a 500 spine, port orford cedars and Carbon Excells in a 400 spine. To my surprise and delight all of these shafts shoot reasonably well. I've been trying to find the arrows that shoot the best though.Reasonably well won't do when I go to the woods. I thought I had what I wanted when I shot a few 2217s cut to 28". They were a bit too short though, I need at least one more inch to clear the shelf with a BH. I fletched a few cut at 29" and tried them. Results were OK, not great. So back to experimenting. I read somewhere,(here?), about putting rope or cord into a shaft to increase weight and not effect spine, so I tried it. Yesterday when I got home I grabbed 3 of my XX78 2016s cut at 29". I then took a piece of nylon cord and fed it into the nock end of the shafts. Doing so added 110 grains to increase total arrow weight to 595grs. Out of all the stuff I've been throwing at mt target I think these are the ones I like best. at 20 yards I can consistantly put 3 arrows into a 4" group and they are hitting with authority. Its a big improvement over the 2016s,(which always flew well), without the added weight. I think its time to stop experimenting and go with what I've got. i think I'll try to go stick one into a hog this weekend.
Honestly I don't know Jeff. My best guess is because the weight of the cord is distributed throughout the length of the shaft, and is very pliable, the amount of deflection remains the same. I saw plans to build a homemade spine deflection tester and now I'll have to build one I guess just to find out. I can't remember where I heard of doing this. I do know that so far I like the results. It may take me a few days to get my spine checker built but I'll let you know the outcome. It may very well have an effect on spine and i'm just not aware of it at this point. Ya know, I could have gone through the rest of my days without wondering about this, THANKS A LOT! LOL!
Again, I just don't know and I don't know how to find out. I think, and this is pure speculation, that because the weight is distributed through the entire length of the shaft that dynamic spine will remain constant as long as the inserted weight is pliable. I wish I knew where to find out for certain although I will likely shoot these arrows regardless of the outcome of my research. I guess if I can't find a way to determine dynamic deflection I'll just punt! Its sure got me curious now.
I did the same thing but with heavy gauge weed eater cord, didn't affect my spine at all, just added more weight to the arrow!
The term "dynamic bend" or "dynamic spine" is used because the degree of bending is difficult – if not impossible – to determine without high speed photography. To measure the static spine, an arrow shaft is supported at two points, and a weight is suspended from the middle. The static spine is a measure of the deflection a shaft. The Easton arrow chart states use of a 28 inch span and a 1.94 pound (880 gram) weight. Deflection is measured in inches. (A 29 inch bare shaft, without pile or nock is used for measurement.) The degree of static bend of an arrow, is called the "spine" of the arrow. The degree of static deflection gives a good indication of the dynamic bend of an arrow – stiffer arrows bend less – but the spine does not give a measure of the actual degree of bending when an arrow is shot from a bow. Thats as good as I can come up with on short notice.
Greg. That is the exact reason why it does not effect the spine. Now if you inserted a smaller dia. shaft the spine would change due to the stiffness of the extra shaft.
