Short draw archers can have problems their longer draw brothers and sisters don’t have with speed, kinetic energy (KE) and trajectory.  In this post I discuss recent KE and trajectory results from two of my bows. 

Warning:  This post contains technical content.  If you notice any inaccuracies, please bring them to my attention. 

A bow set-up’s speed rating by itself doesn’t necessarily mean too much.  For instance you don’t see anyone touting speed ratings under 200 fps as that isn’t too impressive these days.  I have a 1994 Hoyt Spectra Fastflite with round wheels that flings aluminum arrows at a blinding 187 fps.  That bow has shot a cut-on-contact Magnus Stinger through a 132 pound feral boar so well that it took two hands and a little back and leg muscle to pull the arrow out of the ground on the other side.  Translating that speed and arrow weight into something usable, such as kinetic energy, allows us to compare our bow’s performance to some generally recommended standards.  Note:  There is some discussion out there regarding KE versus momentum.  I’m not going to touch on that here, but you may wish to check out Archery Report’s ongoing discussion of the subject.

  • Kinetic Energy Recommendations
    • <25 ft lbs = Small Game (rabbits, squirrels, etc.)
    • 25-41 ft lbs = Medium Game (deer, pronghorn, etc.)
    • 42-65 ft lbs = Large Game (elk, bear, feral hog, etc.)
    • >65 ft lbs = Dangerous Game (cape buffalo, grizzly, etc.)

Also, and in balance, there is the consideration of trajectory.  I say “in balance” as a bowhunter has the option of shooting hewn logs with a trajectory arc like that of a volleyball going over the net or screaming pencils with a comparatively flat trajectory.  The hewn logs will have greater KE (although in my calculations there is a point of diminishing returns) and the screaming pencils will have less.  Why does it matter?  It matters, because in the field we don’t always know the exact yardage to the critter.  The shot on that feral hog was about 12 yards.  That bow is not the one I’d want on a modern day mule deer hunt over open, western terrain.  Combining misjudged yardage with an extreme trajectory will likely result in a missed target.  Dave Holt gives an excellent visual description of this in his books Balanced Bowhunting and Balanced Bowhunting II.  Additionally, this article, Arrow Buyer Help – Speed and Kinetic Energy from Hunter’s Friend is a great resource.

KE and Trajectory Results

Using the same set-ups presented in Short Draw Bow Speeds and Technical Discussion here are the KE and Trajectory Results.

Note:  KE can be computed by the following formula, (Arrow Weight x (Speed x Speed))/450800.  For example ((376.8 grains x (274 fps x 274 fps))/450800 = 62.75 ft/lbs.  Also note that the first KE figures given below are initial KE calculated using this formula.  As the arrow slows terminal KE will be less.  The terminal KE and trajectory figures given below at the indicated yardages are calculated using Archer’s Advantage software. 

2009 Bowtech SWAT – 376.8 gr arrow

  • 26 5/8″ measured to AMO standard
  • 69.75 lbs (maxed out)
  • 14.6 gr on string (Fletcher TruPeep 8.8 gr, string loop 5.1 gr, tied string nocks .7 gr)
  • 376.8 gr arrow
  • 274 fps (three arrow avg)
  • 62.75 foot pounds KE (initial, actual)
  • Calculated downrange KE and trajectory:
    • 20 yards – 8.9 inches drop, 58.1 ft/lbs KE
    • 30 yards – 20.3 inches drop, 55.9 ft/lbs KE
    • 40 yards – 36.6 inches drop, 53.9 ft/lbs KE
    • 50 yards – 58.1 inches drop, 51.9 ft/lbs KE

2009 Bowtech SWAT – 360.1 gr arrow

  • 26 5/8″ measured to AMO standard
  • 69.75 lbs (maxed out)
  • 14.6 gr on string (Fletcher TruPeep 8.8 gr, string loop 5.1 gr, tied string nocks .7 gr)
  • 360.1 gr arrow
  • 279.3 fps (three arrow avg)
  • 62.31 foot pounds KE (initial, actual)
  • Calculated downrange KE and trajectory (Note that these calculated results seem suspect when compared to the above set up – a lighter arrow in this case should not equal greater KE, but I’m reporting the results as they were generated.):
    • 20 yards – 8.1 inches drop, 60.8 ft/lbs KE
    • 30 yards – 18.5 inches drop, 58.5 ft/lbs KE
    • 40 yards – 33.5 inches drop, 56.2 ft/lbs KE
    • 50 yards – 53.1 inches drop, 54.0 ft/lbs KE

2006 Reflex Highlander – 376.8 gr arrow

  • 26 1/2″ measured to AMO standard
  • 67.25 lbs (maxed out)
  • 69.1 gr on string (1/4″ G5 Meta-Peep 6.5 gr, SIMS Super String Leeches 56.8 gr, string loop 5.1 gr, tied string nocks .7 gr)
  • 376.8 gr arrow
  • 259 fps (three arrow avg)
  • 56.07 foot pounds KE (initial, actual)
  • Calculated downrange KE and trajectory:
    • 20 yards – 9.7 inches drop, 53.2 ft/lbs KE
    • 30 yards – 22.2 inches drop, 51.2 ft/lbs KE
    • 40 yards – 40.1 inches drop, 49.3 ft/lbs KE
    • 50 yards – 63.6 inches drop, 47.4 ft/lbs KE

2006 Reflex Highlander – 360.1 gr arrow

  • 26 1/2″ measured to AMO standard
  • 67.25 lbs (maxed out)
  • 69.1 gr on string (1/4″ G5 Meta-Peep 6.5 gr, SIMS Super String Leeches 56.8 gr, string loop 5.1 gr, tied string nocks .7 gr)
  • 360.1 gr arrow
  • 263.3 fps (three arrow avg)
  • 55.38 foot pounds KE (initial, actual)
  • Calculated downrange KE and trajectory:
    • 20 yards – 9.7 inches drop, 49.7 ft/lbs KE
    • 30 yards – 22.2 inches drop, 47.8 ft/lbs KE
    • 40 yards – 40.1 inches drop, 46.1 ft/lbs KE
    • 50 yards – 63.5 inches drop, 44.3 ft/lbs KE

More Technical Musings

For a later-to-be-announced 2010 adventure I’m trying to deliver 62-65 ft lbs with my set up based on the outfitter’s recommendation.  The new Bowtech SWAT puts me on the edge of that.  The Highlander is quite a bit short of my goal.  It’ll be my back up on this adventure.  My dilemma is whether or not I want to up the ante even more and switch to a reliable, economical solution; aluminum arrows.  I know there are a lot of good carbon/aluminum and aluminum/carbon options out there, but when I compare $50 per dozen, raw shaft, for aluminum to $100+ per dozen for carbon/aluminum or aluminum/carbon (raw shaft) the solution is obvious for me. 

So, putting Archer’s Advantage’s tools to use with a hypothetical set up in the Reflex Highlander, the potential with the lightest aluminum arrow with the proper spine, a 2412, weighing (computed vice actual) 400 grains would deliver 64.7 ft lbs initial KE with a downrange KE and trajectory as listed below.  This is another situation where the generated results are suspect and would have to proven.  For instance, when compared to the results above the arrow drop with this heavier arrow is less at 50 yards than the other two set-ups.   However, KE is significantly higher which is good.  A test arrow would have to be made, weighed and shot through the chrony and then that information fed into Archer’s Advantage to verify the results. 

  • 2412 Aluminum Arrow in the Reflex Highlander (calculated using Archer’s Advantage) 
    • 20 yards – 9.3 inches drop, 57.8 ft/lb KE
    • 30 yards – 21.4 inches drop, 54.6 ft/lb KE
    • 40 yards – 38.3 inche drop, 51.6 ft/lb KE
    • 50 yards – 62 inches drop, 48.7 ft/lb KE

With the SWAT just reaching the lower edge of the desired KE I will be using a full cut-on-contact broadhead, the 4-blade, 100-grain Magnus Stinger for this adventure.  If you have concerns about your delivered KE, regardless of quarry pursued, I recommend the same strategy.  I get a lot of people asking me why I shoot 67.5-70 lbs when, according to them, 50 or 60 lbs will get the job done.  Truth be known I’d shoot in the low 70’s if manufacturers made limbs in the 65-75 lb range.  Typically people who ask me this start out at 28.5 inches or more in draw length and are already exceeding the speed and KE delivered by my set-up even when they are shooting less draw weight.  In my opinion, and this is just my opinion, for short DL archers shooting the most draw weight one can safely and accurately handle is the best way to go.  This is one of the reasons I consistently hit the gym.  Safe and accurate are keys here – if an archer can’t draw his or her bow while sitting in a chair with both feet off the ground then he or she is shooting too much draw weight. 

I’d like to keep the flattest trajectory possible, but it is very important to set myself up with the best penetration possible also.  Note that the minimum difference in drop between any of the four set-ups from 20-30 yards is 10.4 inches on the SWAT’s 360.1 grain set-up.  If I aim at the center of a standard 8 inch kill zone any yardage estimation error greater than about 4 yards (one inch drop per yard) will drop the arrow more than the distance from the center of the kill-zone to a miss – 4 inches.  Due to this I try to mitigate yardage estimation errors by participating in 3D shoots without the aid of my range-finder.  I estimate the yardage, shoot and then range the target to see how close or far away my estimate was.  I also try to use that tactic in addition to shooting with a partner who is superior to me at judging distance so I have the opportunity to judge the range, discuss any “trouble spots” a particular target is posing (long, dark, brushy tunnel vs. open and sunny for instance) and learn from the experience.  Shooting with my friend Gary Martin who has taken the archery Super Slam (defined as harvesting each of North America’s 28, now 29, big game species) accomplishes this.

Recommended resources: 

happy hunting, dv

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