How Gel-Test Guppy Metrics Can Be Used to Evaluate an Expanding Hunting Bullet’s Likely Field Performance, Part 5: Empirically Predicting Meat Damage Using the Guppy-Metric I(V).

By Scott Fletcher

“Too much of anything is bad, but too much good whiskey is barely enough.” – Mark Twain

An expanding hunting bullet that preserves edible meat can be as desirable to hunters as one that produces a large wound volume or consistently exits big-game animals on a broadside shot. This article discusses the Guppy-metric I(V) and how its test value can be applied to empirically evaluate a bullet’s potential for producing meat damage, as indicated by data obtained on the 2023 zebra management hunt.

The vast majority of hunters process and consume the meat of big-game animals. Meat damage produced by an expanding hunting bullet can be a primary consideration in its selection. In North America, the preferred shot placement for meat preservation is on the lungs because it keeps the desirable shoulder meat, heart, and liver from being damaged.

Standard practice for trophy hunts in Africa is to place the shot on the animal’s shoulder both to debilitate its mobility and potentially take out the heart as well as both lungs. The primary intent for this shot placement is animal recovery, as the trophy fee is charged for a wounded but unrecovered animal. A recovered animal’s meat is processed for human consumption, with a portion of the trophy fee allocated as compensation for the meat damage caused by shot placement.

Damaged meat is simply bloodshot tissue caused by the hydraulic fracturing of capillaries from passage of an expanding hunting bullet. Damaged meat has a putty-like texture/consistency and can be scraped away from edible meat with a knife (as opposed to being cut). A geotechnical engineer’s interpretation of the hydraulic fracturing mechanics within the capillaries that produce bloodshot tissue is described in section 11.18.1 on page 38 of the 2023 huntreport and in an article found here.

The Guppy metric representing the qualitative degree of inedible bloodshot meat (BSM) is I(V). (Refer to Guppy Techand theGuppymodel.) I(V) is the calculated dimensionless ratio of the modeled bloodshot tissue volume V(S) divided by the inferred volume of the actual hole made by the bullet, V(PS). The intent of I(V) is to numerically assess an expanding hunting bullet’s ability to produce a high-pressure blood-compression wave, as indicated by a large volume of modeled bloodshot tissue relative to the modeled volume of the actual bullet hole. A high I(V) value represents more meat damage due to a more violent, rapid bullet expansion indicative of such a high-pressure blood wave.

One of the performance criteria for the management hunt was each 30-caliber bullet passing through shoulder tissue had to produce a volume of BSM qualitatively judged to be acceptable. Conversations with multiple South African professional hunters (PHs) indicated a 308 Winchester firing a 165 Barnes TSX produced low meat damage. Out of respect for their opinions, this cartridge-bullet combination was included in my gel testing. These PH’s are practitioners who hunt for a living, quick to identify which cartridge-bullets work (and which ones don’t). Modeling why such a cartridge-bullet combination produced such low meat damage was a necessary “reality check” to properly interpret and judge the field applicability of I(V).

A 308 Winchester (Win) case, loaded with a .30-caliber, 165-grain Barnes TSX (TSX), was selected as the wounding performance-standard cartridge. The 165 TSX was also tested at 135 yards (123 m) to determine all Guppy-metric values, including its I(V) value. 

Photo 18 identifies the 308 Win cartridge loaded with a 165-grain Barnes TSX as well as the 300 Win cartridges loaded with the bullets evaluated on the management hunt. Left to right: a 308 Win case loaded with a solid copper 165-grain Barnes TSX; a 300 Win case loaded with a 200-grain bonded-lead cell Woodleigh Weldcore protected point (WWC); a 300 Win case loaded with a 240-grain Sierra Match King that has been modified with a hand-installed poly tip (TSMK); and a 300 Win case loaded with a 220-grain cup-and-core Sierra Pro Hunter (SPH).

As shown on Table 2, all of the I(V) test values of the 30-caliber candidate bullets referenced in Photo18 were significantly greater than the 5.6 value of the 165 TSX, indicating each would likely produce significant to excessive BSM. The closest I(V) value was 10.2 obtained by the 200 WWC, almost double. The I(V) of the 240 TSMK was 15.1, almost triple. The 240 TSMK’s magnitude was intuitively judged to be representative of the explosive terminal performance expected from the rapid expansion of its frangible, cup-and-core match-bullet generic design.

The (IV) test values indicated the only bullet judged to even have a chance of producing BSM judged to be acceptable was the 200 WWC. Field judgements of BSM produced by this bullet would be necessary to provide context to its I(V) test value.

Conversations with Afrikaner hunters and game-farm owners had indicated the judgement of “acceptable” meat damage was highly subjective. Such judgements were typically made “by eye” with no quantitative determination of either the BSM’s volume or its weight.

The qualitative and highly subjective judgement about the BSM produced by bullets used on the management hunt required impartial assessment by an individual knowledgeable with standard skinning-shed procedures and game-meat processing in South Africa. The PH on the management hunt had 24 years of such experience and was tasked with determining if the volume of BSM was considered acceptable by industry standards. The following narrative and photo sequence describe the skinning-shed procedures typically used to evaluate BSM.

Each zebra was suspended by its hind legs in the skinning shed. The carcass was skinned, noting the bullet’s entrance and exit points as well as the size of the surrounding bloodshot tissue. Photo 19 is of the entrance hole of a front-quartering shot on Zebra Z-7 by a 200 WWC; Photo 20 is of the exit hole. The hide still remaining on the carcass is to the left in both photos.

Any shoulder affected by the passage of a bullet was typically sliced along the zebra’s rib cage and rotated away to expose the BSM created by the bullet. Photo 21 is of Z-7’s nearside shoulder, rotated to the right to expose the BSM. The oval-shaped slice line is visible on the carcass in the center of the photo. The nearside ribs are exposed within the slice line. The actual bullet hole through the shoulder tissue is on the upper right on the shoulder-portion of the slice, with the very-dark red BSM extending down and to the left. Photo 22 is of Z-7’s farside shoulder, rotated away from the carcass.

BSM was scraped away from any exposed shoulders and carcass and allowed to drop on to the skinning-shed floor. Photo 23 is of BSM from both shoulders of Z-7, with the BSM from the nearside shoulder at the top, and the BSM from Z-7’s farside shoulder is at the bottom. The boot in the photo is intended as a reference scale. The PH judged that the volume of BSM was acceptable.

Seven zebras taken on the management hunt had a shot though at least one shoulder to enable an assessment of BSM. Table 5-1 identifies the results of the PH’s BSM judgements as well as key field and bullet data.

Four of the seven zebras (Z-1, Z-7, Z-8, Z-9) were shot with a 200 WWC. The impact velocities of these bullets were within plus or minus 100 feet per second (30.5 mps) of the test impact velocity of 2632 fps (802 mps), indicating the field BSM results were representative of the 200 WWC’s I(V) test value of 10.2.  In all instances the BSM produced by this bullet was judged to be acceptable.

One zebra (Z-3) was shot with a 240 TSMK. Although the shot was broadside, the bullet was deflected laterally through its thoracic cavity by a nearside rib. The result was only the nearside shoulder was evaluated for BSM. Photo 24 is of Z-3’s nearside shoulder, and Photo 25 is of the BSM that was scraped away, boots for scale. This BSM volume was judged to be unacceptable.

Two zebras (Z-2, Z-5) were shot with a 220 SPH. This bullet visually produced more BSM than either the 200 WWC or the 240 TSMK, to the degree that no effort was made to scrape it off for a photo. Photo 26 is of Z-2’s farside shoulder; Photo 27is of Z-5’s nearside shoulder, and Photo 28 is of Z-5’s farside shoulder. In all instances the word used by the PH to describe the observed BSM was “excessive”.

The 220 SPH’s I(V) value of 11.2 (Table 2) was only 12% greater than the I(V) value of the 200 WWC. This increase can subjectively be considered as “modest”. Simply based on I(V) “numbers”, the BSM produced by the 220 SPH should have been only modestly greater than the BSM produced by the 200 WWC. However, the terminal violence associated with the BSM produced in Z-2 and Z-5 was subjectively far more than 12% compared to all zebras shot with the 200 WWC, even when the impact velocity of the 220 SPH on Z-2 was over 200 fps (61 mps) less than its test impact velocity. The reason for this disparity is likely the same as the one described in Part 3 for under-predicting both the 240 TSMK’s and the 220 SPH’s field wounding: the additional volume of V(S) affected by weight-loss shrapnel was not included in calculating V(ST). As a direct consequence, this volume reduced the 220 SPH’s calculated I(V).

These skinning-shed observations indicate bullets capable of producing significant weight-loss shrapnel, such as the 240 TSMK and 220 SPH, can also produce significant BSM. The implication is the greater volume of shrapnel created by spalled jacket and core shards likely produces a greater volume of BSM. This assessment underscores the importance of including the radial limits of these shards in gel fracture measurements. The resultant increased Guppy-metric volumes calculated from these shard limits better represent both the wounding and the meat damage potential of the tested bullets.

The skinning-shed assessments by the PH indicated the 200 WWC produced BSM considered to be acceptable every time it was used. This result indicates bullets with I(V) test values of about 10 or less will likely produce a reasonable amount of BSM. Based on the 165 TSX’s established reputation for low meat damage and its I(V) value of 5.6, expanding hunting bullets that produce I(V) test values progressively smaller than 10 can be expected to produce progressively smaller amounts of BSM. Likewise, expanding hunting bullets that produce I(V) test values progressively greater than 10 can be expected to produce progressively greater amounts of BSM.

This article, like the four articles prior, have described a process where numbers generated from the shape of fractures in 20% synthetic gel made by passage of an expanding hunting bullet have been used to both conceptually explain and empirically predict wounding reality. Although the process is “new”, the reality it empirically predicts was observed well over 100 years ago by Colonel Townsend Whelen, a US Army Ordinance Corps officer with a lifetime of big-game hunting experience. Colonel Whelen’s field wound observations and assertions of how a bullet creates such wounding are the context for this entire article. Summary conclusions and the context for how to interpret this process and its results are presented here.