How to Select a Hunting Cartridge, Part 2: The Chambering and Bullet Weight.

By Scott Fletcher

“Mad science is, in fact, mad science ……… until it consistently predicts reality. Madness then becomes denying the validity of the prediction”. – Scott Fletcher

Part 1 introduced the notion that a hunting cartridge could be reasonably selected based on an empirical formula relating a cartridge’s bullet weight to the weight of a non-dangerous game animal. Such a relationship is called an empiricism. Empiricisms reduce/approximate complex science and engineering into a simple mathematical equation that reasonably predicts an outcome that can be verified by observation and direct measurement. Empiricisms are common and routinely used in various engineering disciplines.

The following empiricism reasonably relates a cartridge’s bullet weight to a non-dangerous game animal’s weight based on the bullet’s impact velocity:

            EGW is approximately equal to: [(BW)2 x (V) x 7.5] / 1,000,000

Where:

EGW = Estimated Game Weight (non-dangerous), pounds

V        = Bullet Impact Velocity, feet per second

BW    = Bullet Weight, grains

The following notes apply:

1: Do not use this empiricism to calculate dangerous game weight.

2: Actual field weights could vary by 15% or more.

3: The empiricism assumes broadside shots on the shoulder using bullets designed to expand upon impact, with both the lungs and the heart/plumbing directly above the heart as the primary vital organs. Such shots are consistent with a trophy hunt rather than a meat hunt. Animals shot in the lungs should be expected to travel farther because the heart has not been affected and mobility has not been reduced. An increase in travel distance after the shot could result in an increased risk of an unrecovered animal.

4: The impact velocities of the specific (brand-name) bullet selected should conform to the manufacturer’s recommendations.

The equation’s derivation is presented in eBook Chapter 19. Also presented is the methodology of how the equation was empirically related to the weight of each animal based on recommendations/narratives by Robertson, Boddington, and Aagaard.

Note 1) is self-explanatory.

Note 2) identifies the range of weights potentially possible based on the initial calculation. This potential weight range was indicated by data obtained from the Robertson, Boddington, and Aagaard references, as discussed in eBook Chapter 19.

Note 3) recognizes that the majority of the data used to correlate the calculated game weight to an actual animal’s weight were obtained from two African Professional Hunters where shots on the animal’s shoulder to debilitate its heart, lungs, and mobility are considered “standard practice”.

Note 4) identifies a fundamental performance metric for the actual bullet selected. Gel testing shows that a bullet’s wound cavity volume and penetration length both depend on its impact velocity. Reasons are presented in eBook Chapter 10. As this article is written, only one bullet manufacturer (Woodleigh) offers published, recommended impact-velocity ranges for their bullets.

The following is a simple example problem that illustrates manipulation of the empiricism to obtain an estimated game weight (EGW).

Example Problem: An outfitter has indicated the typical weight of a trophy white tail taken at properties under contract is about 300 pounds (136 kg). Typical shots are from blinds at distances less than 100 yards (91 m). Would a 270 Winchester that launches a 130-grain boat tail spitzer at 3100 fps (944 mps) be a reasonable selection?

Example Problem Answer and Discussion: Determining any bullet’s impact velocity first requires going online to identify its BC. Once the BC is determined, online ballistics software can be used to calculate the bullet’s impact velocity at virtually any distance based on the muzzle velocity produced by the cartridge and selected environmental factors.

For a typical .277-caliber, 130-grain boat-tail spitzer, this online process results in an impact velocity on the order of 2900 fps (883 mps) at the maximum expected range of 100 yards (91 m). Substituting the bullet weight and impact velocity into the empiricism yields an EGW of about 365 pounds (166 kg). Note 2) indicates the actual field weight could range from about 310 pounds/141 kg (15% less) to about 420 pounds/191 kg (15% more).

Using an empiricism does not result in a precise, absolute “answer” due to the number of variables involved and the typical gross simplification of the applicable science/engineering. However, a reliable empiricism’s answer can be judged in terms of the risk associated with achieving some desired performance outcome.

In this instance, the EGW of 365 pounds (166 kg) indicates the risk of an unrecovered deer weighing about 300 pounds is likely very low. This interpretation of the calculated weight is in keeping with what virtually every North American hunter positively “knows” is true: the 270 Winchester is an excellent “caliber” where its use on deer/sheep/goats typically results in a recovered animal. As indicated in this example problem, the presented empiricism is judged to typically result in a representative estimate of the non-dangerous game weight capability of any cartridge loaded with an expanding hunting bullet.

What about the 7 mm Remington mag questions posed in Part 1?

An outfitter has indicated the typical weight of a Roosevelt elk cow taken at properties under contract is about 600 pounds (273 kg). Typical shots are at distances less than 350 yards (318 m). Would a 7 mm Remington mag that launches a 154-grain, poly-tipped boat-tail spitzer at about 3100 fps (944 mps) be a reasonable choice? What about a 175-grain, pointed soft-point boat- tail spitzer launched at about 2860 fps (867 mps)?

The 154 grainer has a published BC of .525. From a ballistics program, its impact velocity at the maximum distance of 350 yards would be about 2495 fps (757 mps). Substituting the bullet weight and impact velocity into the empiricism yields an EGW of about 440 pounds (200 kg). If a 15% potential weight increase is considered, the EGW is about 505 pounds (230 kg).

The 175 grainer has a published BC of .427. From a ballistics program, its impact velocity at the maximum distance of 350 yards would be about 2160 fps (655 mps). Substituting the bullet weight and impact velocity into the empiricism yields an EGW of about 500 pounds (227 kg). If a 15% potential weight increase is considered, the EGW is about 575 pounds (261 kg).

These simple numerical evaluations indicate there is an elevated risk of an unrecovered elk cow if the cartridge loaded with the 154 grainer is used, even when a potential 15% weight improvement is considered. Its far-superior muzzle velocity and BC compared to the 175 grainer’s are of no appreciable consequence in terms of a calculated EGW.

The heavier, slower, and BC-challenged 175 grainer results in an EWG that is more than the EGW of the 154 grainer, but is about 100 pounds (45 kg) shy of 600 pounds. Even at the 15% upper-bound EGW of 575 pounds (261 kg), the numerical evaluation indicates using the 175 grainer incurs some risk of an unrecovered, 600-pound animal. Regardless, this simple numerical evaluation indicates there is likely less risk of an unrecovered elk cow if the 175 grainer is used.

With either bullet, there are several ways to reduce the interpreted risk of an unrecovered animal. North American hunters typically aim at an animal’s lungs. A broadside shot on the shoulder with the aim-point on the heart would debilitate the elk’s mobility as well as penetrate both lungs and the heart or the plumbing directly above the heart. Besides debilitating the animal’s mobility, such an aim-point would affect another vital organ, increase the total wound cavity volume, and thus reduce the risk of an unrecovered animal.

Another way to reduce the risk would be to limit the shot distance to increase the bullet’s impact velocity, and thus increase the calculated EGW. For the 175 grainer, limiting its shot distance to about 120 yards (109 m) would increase the impact velocity to about 2600 fps (789 mps), with the EGW increasing to the desired 600 pounds (273 kg). The implication of this calculation is that strategically reducing the shot distance during the hunt to increase both the impact velocity and the odds of hitting the heart significantly reduces the risk of an unrecovered animal.

Some hunters that own a 7 mm Remington mag could now be sideways because they have concluded that this article “says” a 7 mm Remington mag is not an “elk rifle”, incapable of taking any elk, cow or otherwise. Nope.  The calculated EGWs indicate that there is a risk of potentially not recovering an animal in the hunting scenario presented based on the decades-long field experience of an accomplished North American hunter (Boddington) and two African Professional Hunters (Robertson and Aagaard). The risk decreases with an increase in the cartridge’s bullet weight, and can decrease further with a decreased shot distance and an aim point that includes the shoulder and heart.

Each hunting scenario can be different, including paying for a wounded, unrecovered animal. Furthermore, each hunter has a unique tolerance for the risk posed by each scenario. All hunters are free to decide if the degree of risk of an unrecovered animal implied by any EGW calculation is acceptable as well as what measures, if any, are appropriate to reduce that risk. Regardless of the specific cartridge selected for any animal, there is never a 100% guarantee of recovery.

What is presented on hunting forums or videos is simply a snapshot of a unique hunting circumstance. These circumstances could include an impact-point on the spine (intended or otherwise), or a luck-of-the-draw occurrence of “shock”, as discussed here. The outcome described/depicted may or may not indicate consistent/typical performance. (A stopped clock is correct twice a day.) $#!+ happens, and human nature repeatedly indicates folks typically share success, not failure of skill or personal judgement.

What about the 30-06 questions posed in Part 1?

An outfitter has indicated the typical weight of a trophy zebra at properties under contract is about 720 pounds (327 kg). Typical shots are off sticks at distances less than 200 yards (182 m). Would a 30-06 that launches a 165-grain, poly-tipped boat-tail spitzer at about 2960 fps (898 mps) be a reasonable choice? What about a 180-grain, poly-tipped boat-tail spitzer launched at about 2820 fps (855 mps) or a 220-grain soft-point (semi-rounded) spitzer launched at an anemic 2410 fps (731 mps)?

The 165 grainer has a published BC of .447, and its impact velocity at 200 yards is about 2560 fps (855 mps). The resultant EGW is about 520 pounds (236 kg). The 180 grainer has a published BC of .480, and its impact velocity at 200 yards is about 2490 fps (755 mps). The resultant EGW is about 600 pounds (272 kg). The 220 grainer has a published BC of .294, and its impact velocity at 200 yards is about 1880 fps (570 mps). The resultant EGW is about 680 pounds (309 kg).

As with the 7 mm Remington mag example, these calculations show that the EGWs increase with increasing bullet weight despite a decrease in both muzzle and impact velocities. In the case 0f the 220-grainer, the EGW increased despite both a significantly lower muzzle velocity and BC compared to the other choices.  

No EGW, as initially calculated, is at or above the desired 720 pounds (327 kg). However, if a potential 15% increase in EGW is considered, the result for the 220 grainer is about 780 pounds (355 kg), well beyond the maximum animal weight expected. Regardless of this 15% increase, the quick and simple evaluation afforded by this empiricism indicates that selecting the 220 grainer would likely result in the least risk of an unrecovered animal, particularly if it were placed on the shoulder to take out the heart.

Both the 7 mm Remington mag and 30-06 calculation results identify a typical EGW empiricism outcome: the game weight “answer” is lower than what most hunters believe their favorite cartridge is capable of achieving. There is a natural reluctance to accept the notion that their preferred cartridge only launches a “Stinger missile” when a simplistic, “unscientific” empiricism indicates that a cartridge launching a “cruise missile” is likely better. Even worse is the attendant buzz-kill realization that their F-16 rifle really ought to be a B-52 for a particular animal with attendant hunt circumstances. However, such a rifle transformation is potentially feasible, as discussed here.

Regardless of the calculated EGW’s magnitude, the empiricism presented in this article is judged to be applicable for evaluating a non-dangerous game hunting cartridge regardless of the expanding hunting bullet selected. This “one-type-fits-all” approach does not consider either “over-achiever” bullets, as described in an article found here, nor what each individual hunter believes is a “best” bullet. These issues can typically be accommodated by the terminal performance concepts embedded in the empiricism’s notes and are discussed in Part 3, found here.