The 100-Yard Rule
January 04, 2011
For a truly long-range shot, the most important ammunition consideration is sufficient downrange energy. Our technical editor explains how to use 100-yard energy thresholds to pick the right round for that long-range shot.
When hunting in open country, your load needs to carry the energy that's appropriate for the quarry as far away as you're prepared to shoot.
Most conventional hunting ammunition is designed for optimum performance at about 100 yards. This is the average distance at which the great majority of all hunting shots is fired--as reported by countless surveys by numerous wildlife agencies--and therefore, it is the distance from the muzzle that most conventional hunting bullets are designed to achieve their peak efficiency at in terms of upset and expansion.
Hunting bullets are engineered to operate within a particular velocity window, depending on their caliber, weight, and construction. Below a certain "threshold velocity" they don't upset satisfactorily upon target impact. At excessive velocities, they may upset too rapidly and come apart or fragment after only shallow penetration, without retaining sufficient mass or energy to penetrate reliably into the quarry's vitals.
In general, most hunting rifle cartridges are loaded with bullets that enter their window of optimum velocity performance at around 100 yards from the muzzle. If you shoot an animal at extremely closer range, such a bullet may overexpand and fragment and not deal an immediate death blow. At distances beyond the limits of the optimum window, the bullet may upset only partially (or not at all), likewise not delivering immediate killing effect--particularly with an imperfectly placed hit.
You can get a rough rule-of-thumb indication of where the peak performance window actually lies for a particular bullet by looking at the information provided in the data pages of ammunition manufacturers' catalogs for the lowest velocity cartridge loaded with that bullet. These pages typically show data for "Short-Range Trajectory" (or "Average Trajectory") and "Long-Range Trajectory" with zero distances and trajectory profiles for shooting at different ranges.
The most common short-range zero is 100 yards, and the most common long-range zero is 200 yards, which is an indication that the peak performance window for most hunting bullets comes at velocities from 100 to 200 yards from the muzzle. You may find that same bullet loaded in higher-velocity cartridges with the same zero ranges on the data charts, but the lowest velocity loading is the one that gives you the best indication of its optimum performance window.
You can also use this information as a general indicator of the effective range of a particular cartridge loaded with that bullet. For example, the cataloged short-range zero for Remington's 150-grain SPCL .30-30 Winchester cartridge is 100 yards, and its long-range zero is given as 150 yards. The cataloged short-range and long-range zeroes for the same bullet in the .30-06 Springfield and the .300 Winchester Magnum are the same: 150 yards and 200 yards. This data can be interpreted to indicate that the slower-velocity 150-grain .30-30 finds its optimum performance window between 100 and 150 yards at 1,900 to 1,725 fps velocity, and that its effectiveness deteriorates past that. But does this also mean that if you shoot this same 150-grain bullet past 200 yards in a .30-06 or a .300 Win. Mag. its performance deteriorates at the same rate?
Not really. We need to look closer.
Applying The Rule
Everywhere we turn these days, we're bombarded with advertisements and magazine articles about "long-range" ammunition, "long-range" optics, and "long-range" rifles. Most hunting shots still come at close to medium ranges, and being able to make a long-range shot requires special personal preparation and circumstances. But if you're approaching a hunt where you think a truly long-range shot may present itself, the most important ammunition consideration is sufficient downrange energy. Even if your cartridge can deliver pinpoint accuracy at long range, it won't do you any good unless it delivers enough energy to let its bullet perform as designed once it gets there.
I use the "100-yard rule" when selecting long-range hunting loads. As an example, for whitetail- or pronghorn-size game, I take the classic .30-30 as my reference point. A typical 150-grain .30-30 load delivers about 1,300 ft-lbs of energy at 100 yards, which is universally considered appropriate for these animals. A typical 150-grain .300 Win. Mag. load delivers 1,300 ft-lbs at nearly 500 yards.
A 150-grain 7mm Remington UltraMag (RUM) delivers 1,300 ft-lbs all the way out to about 650 yards. These figures tell me the "hundred-yard equality" distance for those cartridges compared to the energy of a .30-30. For bigger game such as elk or bear, I'll select a baseline cartridge such as a 200-grain .338 Federal and compare its 100-yard energy to the long-range energy profiles of the same-weight bullets in a .338 Win. Mag. or .338 RUM.
If we look at the full catalog information cited earlier for the Remington 150-grain SPCL bullet loaded in the .30-30, .30-06, and .300 Win. Mag., we see that the .30-06 matches the velocity and energy of the 100-yard .30-30 at 400 yards, and the .300 Win. Mag. matches about 75 yards farther out. So even though the manufacturer optimizes the long-range trajectory profiles for the two more powerful loads at 200 yards, we can see that their upset performance window (i.e., velocity and energy) at 400 to 450 yards is the same as the .30-30's at 100 to 150 yards. A deer or antelope hit with a 150-grain SPCL bullet at 400 to 450 yards from the .30-06 or .300 Win. Mag. thus suffers the same impact as being hit at 100 to 150 yards with the .30-30. Dead right there.
When making such comparisons, it's beneficial to match calibers, bullet weights, and bullet designs as closely as possible. Subtle differences in upset designs, ballistic coefficients, and penetration characteristics can create large variables, particularly at extended ranges. For example, Remington's .300 Win. Mag. 150-grain SPCL load carries only 1,425 ft-lbs energy at 400 yards, while Federal's .300 Win. Mag. 150-grain Speer Hot-Cor SP load carries 1,643 ft-lbs at 400 yards due to the Speer bullet's slightly better ballistic coefficient, even though the Remington load launches at a higher velocity. At a near quarter-mile distance, that can make a difference.
Or consider this one: Let's say your favorite load for 100-yard hunting in the Eastern whitetail woods is a 6mm 100-grain .243 Winchester, but you have an opportunity for a whitetail hunt in Montana where a longer shot is likely. You go looking for a similar-caliber, longer-range load in the same bullet weight, and your search of the catalog charts shows you a 6.5mm 100-grain .25-06 Rem. that carries about 92 percent as much energy at 200 yards as your .243 Win. load does at
100. That essentially doubles your effective range, but you might be even better off looking at a 6mm 100-grain .240 Weatherby Magnum load that offers 96 percent of your .243's energy at 300 yards.
The kind of direct comparison you should be looking for when considering reaching out from your familiar woodland rifle to an open-country rifle is illustrated by a comparison of the classic Remington 140-grain Core-Lokt bullet in the popular 7mm-08 to the same bullet in the 7mm Rem. Mag. and 7mm RUM. The 7mm-08 is a superb 100-yard whitetail, antelope, and mule deer cartridge, delivering about 2,100 ft-lbs at that distance. The same bullet delivers the same 2,100 ft-lbs at 250 yards from the 7mm Rem. Mag. and at 350 yards from the 7mm RUM. That tells you something useful about the identical bullet with identical flight characteristics and identical upset characteristics in different cartridges.
Handgun hunters can use these same comparison tools. For many years, the most popular revolver
cartridge for woodland whitetail hunting has been the classic 240-grain .44 Magnum, which is an excellent 50-yard load for that purpose. Its energy at 50 yards is about 900 ft-lbs, which is why shot placement is as important to handgun hunters as it is to bowhunters. Need something a little more energetic and long-range to take a revolver mule deer in the open country of Utah or Colorado? A look at the ballistic profiles will quickly tell you that the .460 S&W Magnum delivers energy equivalent to the .44 Mag.'s 50-yard level as far out as 200 yards, depending on the load.
You can also reverse engineer the process if you use rifle cartridges in a hunting pistol such as the T/C G2 Contender or Encore. Simply check the catalog data for your cartridge's energy profile and optimum performance distance in a standard rifle-length reference barrel, and then compare that to the load's measured velocity/trajectory profile from your handgun's barrel to determine how far out it will deliver matching effectiveness.
Major ammunition makers' catalogs have remarkably detailed ballistic information in their reference pages. With a little thought, this information can be used to make a great many sophisticated performance comparisons and evaluations. Plus, in today's world of near-universal computer access, these same manufacturers' websites offer you the capability to make direct side-by-side comparisons of specific loads without having to wade through pages and lines of charts. And you are not limited to only factory ammo when making such comparisons. Handloaders can utilize online ballistic software at bulletmakers' websites or any number of stand-alone ballistic software programs to plug in data for their own loads in their own guns and get exact performance comparisons for any downrange distance as opposed to the "nominal" test-barrel results in catalogs.
If you take the time to apply the 100-yard rule when selecting a cartridge and load for your long-range hunting gun and its long-range scope, you will be confident your bullet will be able to do its job effectively when it reaches its target. Of course, you still have to be able to make that shot.