Crossbow bolt FOC

Discussion in 'Crossbows' started by jesse300, Nov 30, 2017.

  1. jesse300

    jesse300 Newb

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    I am shooting Carbon Express Piledrivers and have a FOC of 4%. So far they are accurate,but the group could be tighter. Will increasing the FOC make a noticeable tighter group? I currently shoot 100 grain broad heads. My hold overs on the scope are perfect 20, 30&40yards. Should I try to increase the FOC or “If it ain’t broke don’t fix it”?

    My setup is the Crosman Sniper 370, Piledrivers, NAP Shockwave 3 blade 100 grain. Nikon crossbow scope.

    Thanks and sorry for the ramble.




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  2. chieffan

    chieffan Weekend Warrior

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    I shoot the Carbon Express Cross Bolt, 20" with 100 gr, spitfire mechanicals for cross bows. Arrow weight 470 gr+ and have FOC in the 11-12% area. Out to 30 yds the group is about coffee cup size. I replaced the factory vanes with Bohning 3" bolt vanes for crossbows. When you say tighter group, what is your group like now? Are the arrows going into the target straight or angled off some?
     
    Last edited: Dec 23, 2017
  3. jesse300

    jesse300 Newb

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    They seem to hit the target straight, at 30yards I am averaging 2” groups. Maybe I should just leave it alone, since it’s consistent. I am new to the crossbow.
     
  4. Arkyinks

    Arkyinks Weekend Warrior

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    If it is really 4% your groups should be huge! But if you can group then do not mess with what works.
     
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  5. jesse300

    jesse300 Newb

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    If you are getting 11% I wonder if I figured incorrectly.

    I may measure it again to be certain.



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  6. Cottontop

    Cottontop Weekend Warrior

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    I have three different setups (3 different bows) all of my arrows are 18% or heavier. What formula are you using to figure front of center? The only reason I ask is there are a few variations.
     
  7. chieffan

    chieffan Weekend Warrior

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    Sorry for the delay in getting back. the formula I sued is: %FOC = (100 x (A-L/2)) /L .
    A is the balance point from the center of the knock and L is the length of the arrow from the center of the knock to the end of the shaft.
     
    Last edited: Mar 3, 2018
  8. 4315bowh

    4315bowh Newb

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    I was shooting Piledrivers with 100 gr Ramcats; 3 shots, 3 deer (one dropped in her shadow). Then I put on 36 gr lighted nocks and my target bag started moving around on me. Couldn't get any consistency. Checked FOC; <4% on lighted nocks; >11% on original nocks. I'm redesigning my bolts to get extreme FOC (EFOC) of >19%. I'l repost after I try them out.
     
  9. Sharpshaft

    Sharpshaft Newb

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    Hi Jesse300, did you ever recalculate the FOC? I'm interested in finding it out for the Carbon Express Piledrivers. Does anybody else have them and have a momento to calculate it for me? :moose:
     
  10. wayne73

    wayne73 Newb

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    i just set up my first crossbow and bolts 20" pile drivers with 100 grain rocky mountain first cut broad heads. i ended up with 460 grain over all and about 6% FOC .. nothing custom added straight from box to scales.. how i calculated FOC 21" inch long total from tip to tip so center would be 10.5". balanced was at 11.75" forward then i used the calculator here. https://archerycalculator.com/arrow-front-of-center-foc-calculator/
     

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