How Important is the Spine shooting a Crossbow?

Discussion in 'Crossbows' started by chieffan, Mar 3, 2017.

  1. chieffan

    chieffan Weekend Warrior

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    Have read a lot of different information on arrow spine. I have been shooting the Carbon Express CrossBolt arrow and have good groupes. I like the Bohning Bolt Vanes and have re-fletched my new arrows with them. I checked the spine in water with dish soap added, with the odd vane marked on the nock. They seldom ever come up with the same side up so I am thinking that there is no real difference in the spine on any of these arrows. I did put the odd vane in the same position as it was already marked. Arrows weigh in at 472 with 12.5%. Bow is 150 lb Jackal, rated at 315 fps. From a rest it will shoot a 2-3" group from 30 & 40 yds. depending oh how much the shooter moves around. With this, I don't think there is any need to worry about spine in any arrow I chose. Am I right or way off base ? ?
     
    Last edited: Mar 3, 2017
  2. Arkyinks

    Arkyinks Weekend Warrior

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    Because the shaft is so short, spine is not so important with crossbows. If you were trying to tighten a group up a 1/4 inch spine might be an issue. FOC and total weight will effect flight more than spine. Spine is a relation to weight per inch.
     
  3. randy3003

    randy3003 Weekend Warrior

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    Arky is absolutely correct. because of the shorter lengths of our xbow bolts there is very little arrow flex there for controlling it with a heavier or lighter spine isn't nearly as important as the weight of your arrows. Remember heavier is quieter and of coarse lighter is faster therefore allowing you to shoot through smaller shooting windows because of less drop in the flight path of the arrow.
     
  4. Cottontop

    Cottontop Weekend Warrior

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    I couldn't disagree more. Depending on distance and poundage, correct spine(and where it is indexed) will mean the difference between busting nocks at 50 yards and getting a shotgun pattern. Granted, I will never attempt a shot at a live animal at 50 yards but, having that arrow flight as true as possible at long yardage will transfer every bit of energy where it is needed at any distance.
     
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  5. Arkyinks

    Arkyinks Weekend Warrior

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    In carbon bolts you will not notice a spine rating. In carbon arrows you will see spine ratings like 340 or 400 ect and for length of arrow and draw weight you will select the best spine rating. In vertical bows the shaft is at the mercy of the string because as soon as you release the string the shaft is unsupported and absorbing the power.

    A bolt is laying on the rail of an xbow during launch and some of the flex is transferred to the rail and as well the string is supported as well. Lighter bolts (gpi like 7) will flex more than a heavier gpi (gpi like 13) bolts. Most xbows will give you a minimum bolt weight but this does not mean most accurate. The total weight and FOC will affect how the bolt reacts to the launch.
     
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  6. Cottontop

    Cottontop Weekend Warrior

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    I totally understand spine ratings. The point I am making is if you have a spine tester( preferably one with a dial indicator) you place the arrow between two points in this case the rollers should be about 19 to 20" apart depending on your arrow length. A weight is placed on the center of the arrow(about 2 pounds) to cause a mild deflection. At this point you rotate the arrow shaft until the dial indicator reveals the highest point( this is the spine of the arrow) you mark this spot and glue the cock feather along this axis. By indexing all your arrows in this manner you will find your groups will shrink dramatically. Even though crossbows shoot off a rail there is still quite a bit of flexing that goes on between launch and flight. There is also quite a bit of difference between recurve limbs and compound limbs with regard to spine.
     
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  7. tynimiller

    tynimiller Legendary Woodsman

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    Just watch slow-motion videos of bolts....and it will confirm this.
     
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  8. Arkyinks

    Arkyinks Weekend Warrior

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    Looked for some slow motion videos of bolts but could not find one that showed the bolt flexing. BUT I did see some cables and strings bouncing around made me wonder how they did not come unstrung. I have seen wooden shafts out of recurve vbows still wobbling when it hit a 30 yard target.
    As far as indexing the spine to save a 0.0002 in of flex I do not know that it will gain you much more than a warm fuzzy feeling. I index my Snuffers (a 3 blade coc bh) with my vanes so they pass through the same hole with just a tickle. Do not know that it makes a huge difference or any at all but it makes me happy and all my bh's on compound, recurve and xbow are that way. Is it necessary??? Does it make a difference in flight or penetration??? Not really sure but I do know FOC makes a huge difference and heavy has benefits to a point.
     
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  9. Cottontop

    Cottontop Weekend Warrior

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    I agree with you on heavy FOC. Most of my crossbow arrows start in the 18% class and go up from there. My longbow arrows run 21 to 25% Compounds around 13 to 15% Indexing does have merit if you are looking for pin point accuracy. I know there are some who are happy with hitting a grapefruit at 50 or 60 yards, I want to hit bottle caps every time.............
     
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  10. randy3003

    randy3003 Weekend Warrior

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    I don't believe anyone who's shot for any length of time would shoot a 500 spine bolt at 350+ ft/sec. I was only referring to the difference between say a 340 and 300 spine arrow. This little difference is miniscule compared to a 300 grain hunting arrow and one of 400+ grains @ 30 plus yards. A heavier arrow has much more kenetic energy then a lighter one, therefore dispatching the deer in a much more ethical manner. Where a lighter one is quicker but ethically should be used at shorter ranges (say 40 yards or less) . I personally shoot heavier arrows out of my blind (440 grins) @ 375 ft/sec because my bow is fairly quick and has 133ft /lbs kenetic energy. I am very proficient out to 60 yards. And have taken many deer at 50+ yards. My bow shoots both spine the same basically. This is why I say weight over spine, using ones common sense of coarse.
     
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  11. chieffan

    chieffan Weekend Warrior

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    I think most agree that weight and FOC is more important than spine. Apparently my bolts have a low FOC at 12+%. Without changing everything from the bolts up, just how much would the FOC change if I would go from the 100gr to 125 gr. BH ?
     
  12. Arkyinks

    Arkyinks Weekend Warrior

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    Most likely a % or two depending on bolt length. Most of the time with lighted nocks I have to have 100 gr brass inserts with 125 gr bh to get my FOC over 15%.
     
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  13. chieffan

    chieffan Weekend Warrior

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    Will have to check in to getting some brass inserts and do some p;laying around with them. Don't want to do any changing right now as the season is about over. I have been using Carbon Express Cross Bolts, Bohning 3" Bolt fletching and 100 gr NAP Spitfires for crossbows. The mechanicals shoot the same as the field points. Haven't figured the kinetic energy yet. Haven't shot a deer yet either which will probably tell me more than anything.
     
  14. Cottontop

    Cottontop Weekend Warrior

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    Chieffan, After reading your first post, you can do a lot better then 2-3" groups at 30 to 40 yards. If you get time see about getting a few arrows from wyverncreations.com. Dave sells single arrows( Black eagle executioners) very reasonable. I am willing to bet you will see a marked improvement over what you are shooting now. The factory arrows are not indexed but by just moving your nock from vane to vane you can find where the arrows will group tightly. I get my bare shafts from him and fletch with 2" blazers with a high helix and as a result cannot shoot the same spot at 40 yards without damaging an arrow. That is with my slowest setup, a Excalibur 330 matrix shooting a 20" 440 grain shaft at 309 fps. The 20" arrows come assembled with 92 grain brass inserts. I use 100 grain points.
     
  15. Arkyinks

    Arkyinks Weekend Warrior

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    I have bought some bolts that I could not get the inserts out without busting the carbon shaft. So I found some Victory Xbolts with brass inserts to begain with.
     

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