IBO versus AMO

Bows are rated by speed in feet per second (fps). This is somewhat of a bogus figure because most will get nowhere near what the rated IBO speed is in real life. IBO speed is calculated using the following criteria:

Total Arrow Weight = 350 grains (5 grains per lb of draw weight)
Draw Weight = 70 lbs
Draw Length = 30"

WHAT IS AMO BOW SPEED ?

Another speed rating is also AMO rated speed which uses different criteria. The Archery Manufacturer's Organization set this standard for evaluating arrow speed. To discover the AMO Speed a bow is set at:

Total Arrow Weight = 540 grains
Draw Weight = 60 lbs
Draw Length = 30"

For today's compounds, speeds over 240fps are considered fast while anything under 220fps are relatively slow. Usually the real figure is somewhere between the IBO and the AMO speed for the average bow and setup.

WHAT IS MY BOW SPEED IN THE REAL WORLD WITH ITS CURRENT SETUP ?

The only true way to see what speed a bow really shoots at is to take it to an archery shop and shoot an arrow using a chronograph. This is a device that is either free standing or more commonly attaches to the bow by a threaded shaft to the stabilizer hole. An arrow is then shot and a digital readout says what the REAL speed of your arrow leaving the bow is.

My bow is setup to the following using Easton XX78 SS 2314 aluminum shafts:

Total Arrow Weight = 490 grains
Draw Weight = 65 lbs
Draw Length = 30"

So how did my Mathews Ultra 2 SoloCam® actually shape up using a chronograph ? ... 247 fps ... !!!

That may not be even close to the 320+ fps it is capable of, but shooting a 490 grain arrow at 247 fps is not all that shabby either. In fact that is an excellent speed for such a heavy arrow.

HOW TO INCREASE SPEED ?

I could increase my bows speed simply by doing the following:

Increase draw weight. I use 65 lbs rather than 70 because I can still have a very slow, smooth draw when hunting, or
Add an overdraw rest to shorten arrow length & size, therefore bringing down arrow weight, or
Use carbon arrows for less weight also.

For the 2004 season I have swapped to Gold Tip 5575 XT Hunter carbon shafts. That alone has reduced my total arrow weight down from 490 grains to 375 grains and I have gone up to a 70 lb draw weight ... a drop of 115 grains total weight and a 5 lb increase in draw weight had some great results to arrow speed. The deer wont know what hit them.

Arrow and Speed Specs for 2004
Using Gold Tip 5575 XT Hunter Carbon Shafts

Total Arrow Weight = 375 grains
Draw Weight = 70 lbs
Draw Length = 30"

Chronograph Speed = 283 fps
Kinetic Energy = 66.71 ft/lbs

MY FINAL THOUGHTS ?

With all that said and done, although speed is right up there, the real figure I look at when deer hunting is the force (kinetic energy) an arrow hits the deer at. This is measured in foot/pounds (ft/lbs). The minimum is around the 40-45 ft/lbs mark for whitetail deer. My current setup is approximately 67 ft/lbs ...

The last point I wish to make is this, I practice with my bow out to 40 yards (and realistically 20-30 yards for hunting) and get the occasional shot if a deer gets within 30 yards but most importantly I love bow hunting and love just sitting out in a tree stand in the woods. You don't need the biggest, badest, fastest bow to do that ...

... but it doesn't hurt either !