Effective Arrow Weights

MASS WEIGHT OF ARROWS, as opposed to spine weight, affects many aspects of archery: arrow speed, kinetic energy (hitting power), bow noise, shooting safety, and accuracy. Thus, choosing arrows of the right weight for your bow is critical.

Safe Standards

In the past, when everyone shot recurves and longbows, the standard for maximum bow performance was nine grains of arrow weight for each pound of draw weight. Thus, a 60-pound bow would call for a 540-grain arrow.

With the advent of compound bows, overdraws, lightweight arrow materials, improved bow designs, and the growing popularity of 3-D shooting at unknown distances, the trend swung radically the other way until archers were shooting three to four grains of arrow weight per pound of draw weight and achieving arrow speeds of 300 feet per second (fps) and faster.

But they also achieved negative side effects. When a bow launches a heavy arrow, the arrow absorbs up to 80 percent of the bow's stored energy and the bow is safe to shoot. At the opposite end of the spectrum, when a bow is dry-fired--that is, fired with no arrow on the string--100 percent of the bow's energy vibrates through the string, limbs, and handle, and the force can break the bow. The lighter the arrow shot, the closer to a dry-fire situation--and the greater the danger. A decade ago, during the early years of the speed race, cracked handles and limbs, as well as broken strings and cables, were not uncommon. Nor were cracked heads from flying bow parts.

Trying to cap that trend, the International Bowhunting Organization (IBO), adopted a "five grains per pound" limit in 1991 for all of its tournaments. Also, the Archery Manufacturers and Merchants Association (AMO), which sets standards for the archery industry, developed a chart listing safe minimum arrow weights.

Today you commonly hear that the AMO standard is six grains of arrow weight per pound of draw weight. Yes and no. For a bow with speed cams, 60-pound peak weight, and 30-inch draw length, the standard is, indeed, six grains per pound. But from there it varies considerably. Cam shape, draw length, and brace height all influence bow performance and, thus, recommended minimum arrow weight. For example, for a 40-pound bow with round wheels and a 29-inch draw, the recommended minimum weight is 3.75 grains per pound. For a 70-pound bow with speed cams and a 33-inch draw, the recommended minimum is 8.4 grains per pound.

Weight vs. Penetration

People commonly say, the heavier the arrow, the better it will penetrate. That's true--partially. But it really misses the point, and it's true only for a given bow, Indeed, the heavier the arrow, the more of a bow's energy it will deliver to the target. But will a 600-grain arrow always penetrate better than a 400-grain arrow? No.

Let's say one bow shoots a 400-grain arrow at 270 fps, and another shoots a 600-grain arrow at 200 fps. Will the 600-grain arrow penetrate better than the 400? Not likely. In this example, the 400-grain arrow delivers 64.8 foot-pounds (ft.-lbs.) of kinetic energy (KE), while the 600-grain arrow delivers 53.3. In other words, the light arrow produces 22 percent more KE, meaning it has about that much more penetration potential. Yes, at a given speed, a heavier arrow always produces more KE than a lighter arrow. But a heavier arrow traveling at a slower speed does not.

Additionally, switching from a heavy to a light arrow on any given bow has scant effect on KE. Let's say your bow shoots 600-grain arrows at 220 fps. If you switch to 400-grain arrows, arrow speed jumps to about 260 fps. Do you now have a fast arrow but poor penetration? Again, no. The 600-grain arrow generates about 64.5 ft.-lbs, of KE; the 400-grain arrow, about 60 ft.-lbs. You've lost 4.5 ft.-lbs, of KE, or roughly six percent, but you still have 60 ft.-lbs., enough to blow an arrow through a moose, elk, grizzly, or anything else that walks in North America. If you're shooting a lightweight compound or a traditional bow with marginal energy, then you're wise to maximize penetration by shooting the heaviest arrows feasible. But most modern, high-performance bows store so much energy that lack of penetration is not a concern--regardless of arrow weight.

Bottom Line

Think moderation. At the radically light end of the scale, arrows will be sensitive and hard to shoot consistently, and your bow will be noisy and susceptible to damage. At the heavy end, the arrows will fly like logs with a looping trajectory and no zip.

WEIGHING-IN ON LIMITS

Time to repeal antiquated laws

Several states have a minimum arrow-weight limit of 400 grains. That makes no sense. Certainly the AMO chart (visit sportsafield.com to view this chart)--based on scientific testing and engineering knowledge--doesn't support a 400-grain weight limit. Some people say the weight limit is to assure adequate arrow penetration and clean kills. Again, that doesn't hold water. Bow design, draw weight, and draw length govern a bow's energy, and arrow weight is almost irrelevant. An arrow-weight limit does nothing but impede youngsters and archers with short arms from shooting arrows matched to their bows. It should be abolished.

SA FACT

During the twenty-first recording period for the Pope and Young Club, archers recorded whitetail entries (minimum score 125). Of those archers, 95 percent shot compound bows, and 51 percent shot with draw weights of 60-69 pounds; 79 percent used aluminum arrows.

Source Citation:SCHUH, DWIGHT. "Effective Arrow Weights." Sports Afield 224.2 (Feb 2001): 40. General OneFile. Gale. Alachua County Library District. 23 Aug. 2009
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