Does a Bullet’s Weight Loss Adversely Affect Its Penetration?

By Scott Fletcher

“Measure what is important, don’t make important what you can measure”.  -  Robert McNamara

The answer to the question posed by the article’s title is “no”, more likely than not, if the bullet used is heavy enough for the weight of the animal it is intended to take and the bullet’s impact velocity is compatible with its generic design.

There are two categories of penetration, defined as either ineffective or effective. Ineffective penetration occurs when a bullet does not completely breach vital organs contained within an animal’s rib cage (thoracic cavity) from any shot angle. Effective penetration occurs when a bullet completely breaches vital organs contained within an animal’s thoracic cavity, and is either retained by the far-side hide or completely exits the animal for all shot angles except full frontal. For shot angles other than full frontal, the thoracic cavity essentially extends from the near-side ribs to the far-side ribs.

Penetration conforming to these definitions is easily identified in a recovered animal. The actual, observed extent of the bullet’s penetration through vital organs in an animal’s thoracic cavity is the sole basis for determining satisfactory performance, not retained bullet properties. As will subsequently be discussed, retained bullet properties only reflect the bullet’s journey through the animal and can misrepresent the demonstrated terminal performance indicated from both field and autopsy data.

Photo 1 shows an unfired 30-caliber, 200-grain bonded-lead core bullet on the left and one shot from a 300 Winchester that was recovered from a zebra’s far-side hide on the right. The bullet initially breached two near-side ribs and was deflected upward into the spine, perforating the near-side lung and the top of the heart. The bullet then breached the spine, removing about a 2-1/2 inch wide (6.4 cm) by ½ inch (1.3 cm) deep notch. The bullet was then deflected downward and perforated the far-side lung before breaching a far-side rib. The zebra dropped to the shot.

Photo P-19 from the 2023 management hunt report shows the penetration path of the bullet identified in Photo 1 through a zebra’s “rib-to-rib” thoracic cavity. Prior to the photo, the zebra was suspended in the skinning shed and had its vital organs removed. The wooden dowel is aligned with the bullet’s right-to-left path, with the entrance hole on the right. Even though the recovered bullet lost 52% of its weight (weight retained = 48%), its penetration was effective because it completely breached vital organs in the zebra’s thoracic cavity and was retained by the far-side hide. The bullet’s weight loss and expansion ratio of only 1.29 reflect its penetration journey. 

Photo 2 shows a jacket on the right that completely separated from the core of a poly-tipped, 30-caliber, 240-grain match bullet, fired from a 300 Winchester.  The parent bullet is shown on the left.  The jacket was recovered on the far-side hide of a black wildebeest. Even though the jacket separated from the core, the penetration from a broadside shot was effective because both the jacket and lead core completely breached the wildebeest’s thoracic cavity and the lead core exited the animal. In doing so, both the jacket and core breached a near-side and far-side rib, perforating both lungs in the process. The wildebeest sprinted 108 yards (98 m) before piling up.

Photo 1 and Photo P-19 demonstrate that all expanding hunting bullets can be expected to lose weight from mushroom spalling during their penetration journey. For a bullet of any generic design, progressively greater bullet weight loss should be expected with a progressively greater impact velocity and the number and size of bones breached. Bullet weight loss is simply a by-product of the impact and penetration/breaching process.

A bullet with a weight appropriate for breaching the vital organs of the animal being hunted has a reservoir of potentially sacrificial weight that can reduce the degree of momentum loss attributed to spalling during penetration. If a bullet is heavy enough for the animal being hunted and is the proper generic design to satisfactorily withstand the expected impact velocities, any sacrificial weight loss can be (and typically is) inconsequential to achieving effective penetration.

The “weight reservoir” of a heavier bullet is also a “shrapnel reservoir”. As discussed in the article on wounding and in the referenced report, the shrapnel produced from a spalling mushroom beneficially increases observed wounding.

The concepts of having a bullet with a sufficient weight needed to breach vital organs embedded in the thoracic cavity of the animal being hunted and matching a bullet’s generic design to its expected impact velocity based on a defined hunting problem were used to select the 2023 management hunt bullets. The methodology to select a bullet of appropriate weight is described in section 8.3.2 on page 12 of the report. The expected hunt impact velocities for each bullet were checked for compatibility with their generic designs, as discussed in sections 9.2, 9.3, and 9.4 from pages 22 to 25 of the referenced report.

A combined total of eleven shots was required to take the ten animals on the 2023 management hunt. The compiled retained bullet and penetration data for each of the three bullets used are identified in Table 5, Table 6, and Table 7 from the referenced report.

As indicated in these tables, effective penetration occurred in ten (91%) of those shots from a variety of shot angles. Bullets completely exited the animals six of eleven (55%) times even though weight loss of recovered bullets typically ranged from 42 to 60 percent (retained weight ranged from 58 to 40 percent). Furthermore, all bullets selected breached either the spine or the neck vertebrae of a zebra. Other bones breached included the scapula, up to three near-side ribs, and a far-side rib. Such performance demonstrates that the bullets selected by the process in the referenced report had sufficient sacrificial weight to allow breaching substantive bones, enabling each to achieve effective penetration in virtually all instances.

The only time where ineffective penetration occurred was the second shot from a 200 WWC into Zebra Z-6, identified in Table 5. The unusual and unrepresentative circumstances associated with this second shot are discussed in section 12.3 on page 45 of the referenced report. The second shot by this bullet produced a drop-to-the-shot reaction due to hydrodynamic shock even though it failed to penetrate through to the far-side hide. Excluding the second shot into Z-6, this bullet exhibited effective penetration from a variety of shot angles, completely exiting zebras in two of the six (33%) total shots taken.

The Professional Hunter (PH) administering the management hunt had 24 years of experience. He was asked to qualitatively rate the penetration performance of the bullets used. His ratings are shown in Table 9 of the management hunt report.

Both the 240 TSMK and 220 SPH have a cup-and-core generic design. This generic design is typically not well regarded by most PHs and hunters for use on African plains game. This judgement appears to be based on retained bullet properties that are typically assessed as marginal to unacceptable, likely primarily influenced by the design’s tendency to both lose “too much” weight and shed its jacket. However, Table 9 shows both of these “heavy” bullets had field penetrations that were judged to be “excellent”, with the lighter “premium”, bonded-lead core 200 WWC obtaining a “very good” penetration rating. The PH’s bullet-specific judgements were made based solely on demonstrated field performance and skinning shed observations, as no retained bullet data, such as weight loss and mushroom diameter, had been obtained.

The PH administering the hunt offered the following unsolicited assessment of the 240 TSMK: “Of all the 300 Winchester bullets I have seen, the 240 TSMK is rated excellent as a trophy bullet. No other bullet is comparable”. Note that this assessment was made with the knowledge that this heavy, highly frangible match bullet had shed its jacket during its penetration journey through the black wildebeest.

The PH’s judgements underscore that any logical and realistic evaluation of a bullet’s terminal performance, including its penetration, should be based on field and autopsy data rather than retained-bullet properties. Applicable field data needed to critically evaluate a bullet’s penetration include shot distance, estimated impact velocity, shot angle, distance traveled after the kill shot, and the relative volume of blood produced that can be judged suitable for tracking. In addition to determining if effective penetration was obtained, applicable autopsy data include the type and number of bones breached, the vital organs breached, the degree of wounding obtained, and the degree of meat damage.

Such field and autopsy data enable any hunter to make an informed and reality-based evaluation of the bullet’s penetration as well as its overall terminal performance. If the bullet does not demonstrate effective penetration or is otherwise judged to perform unsatisfactorily, these data enable a strategic choice of either a heavier bullet of the same generic design or an alternative bullet with a different generic design that better serves a hunter’s personal terminal performance objectives and tolerance for risk.