As you search for your next new bow, look at reviews and the bow makers web sites to understand the bows performance. All makers will list the bows IBO speed. (IBO speed comes from a 70 lb bow shooting a 350 grain arrow) that is an arrow weight of 5 grains per pound of draw.
Because they post the speed and you know the arrow weight you can calculate KE this way
IBO speed x IBO speed x arrow weight of 350 gr. Divided by 450240 (mathematical constant) Here is an example
315 x 315 x 350 divided by 450240 = 77.1 KE.
Since the draw weight they used is 70 lbs, you take the KE and divide it by the draw weight.
77.1 KE divided by 70 lbs draw = 1.10 efficiency.
Efficiency is just the amount of draw weight you have to pull back vs what you get for that effort in terms of KE and momentum. I suggest steering clear of bows that fall below 1.0 efficiency because you have to work harder (pull more draw weight) to get more out of the bow and because most bows today are above 1.0, you don’t have to select an inefficient bow
Outdoor life just did a review of 11 new bows. Using the info from their test (70 Lb bow shooting a 350 gr. Arrow) I derived the following efficiencies.
Bowtech Insanity CPX = 1.28
Darton DS 3900 = 1.25
Strother Wrath = 1.24
PSE EVO 7 = 1.19
Mathews Heli-m = 1.15
Hoyt vector 32 = 1.14
Ross Crave DRT = 1.08
G5 Prime = 1.05
Bear Anarchy = 1.05
Mission Riot = .97
Parker Velocity = .92
Once you find the most efficient bows based on the data, understand that you wont be shooting the 5 grains per pound of draw from the tests and will see even more efficiency when you shoot a hunting arrow weight in the 6, 7 or 8 grains of arrow weight per pound of draw.
But you say you’re not a 70 pound bow shooter (they are becoming rare) and you want to instead shoot 55 or 60 pounds of draw, never fear, the efficiency from the test was a product of draw weight vs KE which was derived from a fixed arrow weight per pound of draw. You can expect that same efficiency with lower draw weights since its inherent to the design of the bow.
Next, go to several dealerships and shoot the bows that are high in efficiency to evaluate their noise and hand shock and comfort. You may find the most pleasing bow is not the most efficient but when you do your evaluation insist (since its your money and you are the customer) that you shoot arrows that are in the 6 or 7 grains per pound of draw weight you plan to hunt with. Don’t let them make you shoot a super light arrow just to show how fast the bow is. Why would you want to test drive a bow that is not in the configuration you will be using???
You may find that while marketing and hype and fan-boy-ism tells you that you should be buying a Mathews or Bowtech, your homework done in advance and your test drive may have you selecting a Darton or Strother because its more efficient and feels better.
In the end, you may be getting the same KE (penetration) from a 50 Lbs PSE or Hoyt than you could get from shooting a 60 Lbs Mathews or Bowtech. Do your homework and forget the hype. Your buying performance, not a brand name. Calculate the numbers, shoot some bows and make an informed choice. You may find that the least efficient and performing bow feels the best in your hands. You will just need to shoot a higher draw weight to get the same KE, MO and speed that you could have got from a more efficient model.
Formerly Retch Sweeny