Home Forums Bows and Equipment A heavy arrow that shoots flatter than a lighter arrow! Reply To: A heavy arrow that shoots flatter than a lighter arrow!

Ed Ashby
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Because this is a subject not well understood the following is a follow-up posting I made in reply to a question about how this can be. How does it not defy the Law of gravity.

“Nope, the law of gravity is being well enforced. As you’ll remember from grade school science, the pull of gravity is a constant, not dependent on the weight (mass) of the object. The Gravitational Constant is 32.174 feet/second/second at sea level. A falling body drops at this rate, regardless of its mass.

(1) A higher mass arrow absorbs more of a bow’s stored energy, and will carry higher kinetic energy than a lighter arrow from the same bow.

(2) If more of the arrow’s energy is applied to the arrow’s forward motion then the arrow will travel farther before it drops to the ground. A more efficient arrow design does exactly that; it conserves energy otherwise wasted on ‘non-productive work”, such as recovering from paradox and/or stabilizing arrow flight.

(3) A heavier arrow which derives greater energy from the bow and which also is of a design that makes more efficient use of whatever energy it derived from the bow can have an equal or shorter travel time across a given distance; ergo, gravity has an equal or lesser time to act upon the arrow and the drop at that distance will be equal or less.

As previously noted, several compound shooters who approached me at the ATA reported that they were getting equal or less drop at 20, 30 and 40 yards with a heavier arrow having EFOC than with a lighter arrow at low FOC (and in one case the shooter reported that he had tested to 60 yards, with the same results). The aggregate of reported results indicated that an EFOC arrow in the 24%-25% range shot to the same point of impact as a low FOC (in the 5% to 6% range) that was 150 to 175 grains lighter. This is congruous with the results I’ve had with equally tuned, equal mass/profile arrows; the equal mass, higher EFOC arrows shoot flatter (drop less) than the lower FOC arrows. This can only occur when the flight time is less. Since I was testing with equal mass arrows, equally well tuned, the bow derived force would be equal. For the flight time to be less the EFOC arrow has to be using its bow-derived arrow force more productively than the lower FOC arrow. This additional ‘productive arrow force’ can equally well be applied to pushing a somewhat heavier arrow fast enough to result in a ‘total flight time’ equal to that of the lighter arrow, resulting in equal arrow drop.

Now those compound shooters are generally working with more ‘potential bow force’ than most of us traditional shooters. That means a higher potential ‘useful force’ gain (from the same amount of increase in arrow efficiency), but the effect would be the same for a traditional bow, but to a somewhat lesser degree – dependant only on the amount of available force (at equal arrow efficiency).

It’s all about total flight time. Ask any competition 1000 yard rifleman which .30 caliber bullet shoots flatter (has less drop) at 1000 yards, the 200 grain Match King or the 180 grain Match King, when fired from any of the .300 Magnum cartridges commonly used in 1000 yard competition. It’s the 200 grain bullet, even though it starts out well over 200 fps slower than the 180 grain version. Why? Because it makes more efficient use of the energy it carries. Indeed, beyond 600 yards it will be traveling faster than the 180 grain bullet. The net result is a shorter total travel time to reach the 1000 yard target, giving a sorter time for gravity to pull on the bullet, which results in a lesser amount of bullet drop. Bullets are a far more efficient aerodynamic design than an arrow, which also means that the potential for gains in efficiency are far greater for the arrow, percentage wise.

Hope this helps clear up the gravity question,
Ed”