While there are other factors to consider when setting up an accurate compound bow for hunting, all bowhunters want to shoot as fast an arrow as is practical. A fast arrow has a flattest trajectory possible, and that’s a good thing, for several reasons, the two biggest being the leeway in aiming at a distant target at an unknown range, and the fact that the faster the shaft, the more kinetic energy it has when it reaches the target. There are several factors that go into the arrow speed equation. When shooting a compound bow, all things being equal, they are:
1. Draw weight: The more draw weight you pull, the faster the arrow will fly. The rule of thumb is that for every one pound of draw weight your bow is reduced, raw arrow speed is reduced 1½-2 feet per second (fps).
2. Draw length: A longer draw length creates a longer power stroke than a shorter draw length, allowing the bow to store more energy. The rule of thumb was that for every added inch of draw length, you increase raw arrow speed approximately 10-15 fps.
3. Arrow weight: The rule of thumb is that, using a 70-pound draw weight bow, for every 3 grains of added arrow weight for arrows weighing near 350 grains, you will drop raw arrow speed by 1-2 fps, and for arrows weighing closer to 450 grains, you’ll see a drop of closer to 4 fps for every 4 grains of arrow weight added.
4. Bowstring weight: Adding weight to a bowstring (peep sight, string silencers, string loop) will affect raw arrow speed, but not by much. Generally speaking, adding 20 grains of overall weight to the string will only deduct about 5 fps off the raw arrow speed.
Many bowhunters don’t quite understand the complexity behind bow speeds. They see a speed rating listed on a website, and assume they will get that raw arrow speed, or maybe a little better, if they buy that bow. But that rarely happens, and here’s why.
There are two standard methods of estimating — and selling — the raw arrow speed of a compound bow. The IBO method sets up a bow with an arrow weighing 5 grains per pound of draw weight. The second common speed rating is the ATA rating, which uses a 30-inch draw length, 70-pound draw weight, and 350 grain arrow. Thus, when a manufacturer touts its bow as having a speed of, say, 350 fps, the truth is that a hunting weight arrow of 400-450 grains from that same bow will initially leave the bow much slower – especially if the draw weight and draw length are significantly reduced. There are several online arrow speed calculators that are fun to play with, including http://backcountrybowhunting.com/calculator/ and https://archerycalculator.com/estimate-bow-speed/, among others. However, you have to shoot your hunting weight arrow through a chronograph to know exactly how fast it is flying. And remember, in bowhunting speed is good – but it is far from everything.
