Archery calculations

Discussion in 'Bowhunting Africa' started by Diamondhitch, Mar 5, 2012.

  1. Diamondhitch

    Diamondhitch AH Legend

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  2. mudslinger

    mudslinger AH Veteran

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  3. Packsy

    Packsy AH Senior Member

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    I have a really good formula for calculating my hunting set up.
    It is.... wait for it.... wait for it..... STRETCH!!! ;)
     
  4. Stretch

    Stretch AH Fanatic

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    It is nice to share this information with our fellow archers. These calculations have allowed me to make changes to increase equipment performance. Currently I am playing with Packsy's arrows to increase her Kinetic Energy. What I discovered is that by adding a heavier broad-head the FOC (front of center) went to 16.4% which is higher than the manufactures recommended 15%. By simply adding a lighted nock or an arrow wrap I was able to bring the FOC within desired spec(14.7%). The result is increased Kinetic Energy and good arrow flight. What did we do b4 the internet?
     
  5. Diamondhitch

    Diamondhitch AH Legend

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    I think it is nice for someone contemplating a new setup to be able to compare apples to apples by converting IBO into the actual speed they will acheive. I was astounded that I could purchase a bow these days that will mirror the performance of my current bow using an arrow just 18 grains lighter after DROPPING 20LB OF DRAW WEIGHT! Ooooooo if I only had the time and money.
     
  6. mudslinger

    mudslinger AH Veteran

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    Stretch, I would not necessarily look a the 15% FOC being the threshold as being the optimum FOC for a set up. I increased mine to over 18% and am very happy. Also, do some calculations on your's and her's MOMENTUM. this is the area you really need to be looking at to see what is going to give you the best set up. Momentum is the ability of the arrow to penetrate, not KE. Do not get me wrong, KE is good, but a large increase in momentum is what you are looking for. i increased my arrow weight by 150 grains and only increased my KE by a very small margin, but my momentum jumped drastically. I did this weight increas also via insert wieght to get my FOC way up. This increase in FOC also made my set up more forgiving, more accurate at longer distances and my bow noise on the shot vanished.
     
  7. Stretch

    Stretch AH Fanatic

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    mudslinger, I have always used 8-15% FOC only because it is the manufactures guideline. My reason for not exceeding the 15% FOC was I assumed there would be extra drop in her arrows making it tougher to compensate especially at the longer distances. Mass X Velocity = momentum makes sense.
    I did notice the leveling off of KE as I added arrow weight yet the momentum continued to increase. I can see momentum as an important factor. We are are going to play with some combinations this weekend. Thanks for the heads-up.
     
  8. mudslinger

    mudslinger AH Veteran

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    Even with me adding 150 grains to the front of my arrow, my pin gap did not widen that much out to 60 yards. Let us know what you come up with on your combos this weekend. It is actually a lot of fun and eye opening when you do some of this playing with your set up, arrow weight and FOC. I have been for a long time a speed freak, but now realize the benefits of a heavy arrow and a lot of FOC. My next biggest project on arrows after this year is finding an arrow that weighs between 800 and 900 grains with a single bevel COC BH with the FOC above 15% for a Cape Buffalo hunt I am looking at in 2014. Should be interesting as the spine I am looking at for an FOC like that is somewhere around .233 spine.
     
  9. Stretch

    Stretch AH Fanatic

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    There is a reason Fred Bear and Howard Hill used heavy arrows. I have never been a speed freak, always leaning toward the heavy side with my arrows. The set-up I am playing with is Packsy's. With her light draw weight (currently 38 lbs) changes seem to have a bigger impact. She has a self-imposed shot distance limit of 30 yards so that tempers the effects of change somewhat. She is working on conditioning to increase her draw weight. Things will change even more. I will know the results.

    Cape buffalo with your bow. Sweet!!! Have you read Dr. Ashby's report on single bevel broadheads?
     
  10. mudslinger

    mudslinger AH Veteran

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    I have the report in my favorites. My PH made the suggestions for the arrow, now I jsut have to find the right combo. I knew the set up was Packsy's and was touchy as far as changing anything. I know that on the 2 trips I have been on, the majority of my shots out of a hide were standing so it should be a little easier to draw standing than it is sitting. I have always told people that if they think thye candle handle the draw weight, to sit down in a chair and if they could not draw the bow back smoothly while not moving the bow arm up or down or right or left, then they are probably good on the weight. I have seen people that could draw a bow standing, but put them seated in a chair and they coud not draw the bow back smoothly without some major bow arm manipulations to get it back.
     
  11. Stretch

    Stretch AH Fanatic

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    Good point. She does practice both sitting and standing positions.
     
  12. Stretch

    Stretch AH Fanatic

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    In order to increase arrow mass I changed Packsy's arrow tip from 75 to 100 grain. I found no appreciable change in point of impact and the 100 grain G5 striker flew extremely well. Her Carbon Express arrow are spine for 30/50 so as she increases draw weight they should suffice with the added tip weight. I am going to experiment increasing arrow weight even more. I plan on adding a 10 grain wrap and was looking at 2 grain per inch weight tubes. Instead of investing in weight tubes right away I had an idea. I plan on picking up some standard air hose tubing at our local farm store. It comes in various sizes so I hope to find a snug internal fit as to reduce movement inside the shaft. It is only a few pennies per foot and will allow me to experiment b4 investing in actual weight tubes.
     
  13. mudslinger

    mudslinger AH Veteran

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    Stretch, sound like you like to tinker also. keep us informed of your findings. I would love to see what you come up with on the lighter weight low paundage set up.
     
  14. Stretch

    Stretch AH Fanatic

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    Ya I like to tinker. just don't start calling me "Tinkerbell":)

    Here is the skinny so far with Packsy's set-up.
    #1-I am going to slowly let her work the bow weight up. I bumped it up 1lb so she is now at 39lbs and she is handling it well.
    #2-Last week I changed her broadhead from 75 grain muzzy to a 100 grain G5 striker. Adding 25 grains point weight made no change in the point of impact and more penetration was the result. Nice. This was a good move.
    #3-Tonight I added 28 grains of tube weight to one of her arrows. At 20 yards she had 5" point of impact drop with very limited penetration difference. Not good. To much weight versus current draw weight. I will visit this again if her bow weight moves up to 43-45lbs.

    Current set-up is performing well FOC is 14% Her finished arrow weight is 332 grain which is 8.51 grains per pound. A relatively heavy arrow at that draw weight. At some point I am going to tinker by adding a 8-10 grain arrow wrap. This may be a good balance. Time will tell.
     

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