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.45ACP vs. 9mm: Part II

By Charles Schwartz
April 23rd, 2018

In Part I of this examination of the “.45ACP vs. 9mm”, an “apples-to-apples” comparison of the respective lethality of the 9mm and the .45 ACP was undertaken using similar non-deforming projectiles as typically found in their military full-metal jacket round nose configurations. In that comparison, the 9mm NATO 124-grain FMJ (M882) edged out the venerable .45ACP 230-grain FMJ (M1911) by a small 2.03% margin in terms of the probability of incapacitation, or P[I/H], proving conclusively that the old maxim of, “They all fall to .45 ball.”, fails to hold up to even the most cursory examination. In “Part II”, the .45ACP and the 9mm cartridges are examined from the standpoint of how the use of expanding designs (that is, JHPs, or jacketed hollow points) effects their respective lethality.

For those with little familiarity with the mechanics of how JHPs function, a brief explanation is certainly in order. Typically, JHPs function by expanding (increasing their initial pre-impact diameter) after striking soft (animal or human) tissue. This expansion, which increases the amount of tissue damage produced by the bullet’s passage through tissue, occurs when soft tissue, composed primarily of water, proteins and other trace organic compounds, enters the expansion cavity of the JHP at high velocity. The water present in those tissues produces hydraulic forces as it slams into the bottom and sides of the expansion cavity. If the velocity of the soft tissue entering the JHP’s expansion cavity is high enough, the resulting hydraulic forces produced by this action exceed the yield strength of the alloy that the JHP is made of and the walls of the JHP’s expansion cavity deform radially (and hopefully uniformly) outward in all directions resulting in an increased bullet diameter. The expanded JHP’s increased diameter makes direct contact with the tissue surrounding the bullet’s path causing traumatic damage to those tissues. FMJs, of any caliber, tend to pass through soft tissue with minimal damage due to their smooth, rounded profiles producing minimal damage along the way. Jacketed hollow point bullets that expand, with their increased cross-sectional areas and typically stellate shapes with rough or jagged edges, tend to damage more tissue per unit of distance travelled and have higher rates of deceleration which results in greater strain energy related damage to nearby surrounding tissues. Since a bullet’s sectional density is defined as the mass of the bullet divided by the cross-sectional area of the bullet, as the JHP deforms, its sectional density (measured in pounds per square inch) decreases as the mass of the bullet remains the same (hopefully) while the cross-sectional presented area of the expanding JHP increases. The expansion of the JHP also increases the amount of braking force acting upon the leading portion of the bullet causing the bullet to decelerate rapidly limiting its maximum penetration depth.

In order to make an “apples-to-apples” comparison of the .45ACP and the 9mm NATO using JHPs, the mechanics involved in projectile expansion require that we start with projectiles in both calibers having a similar initial sectional density, structural design, impact velocity, and expansion ratio. A JHP’s expansion ratio, one basic measure of a projectile’s terminal ballistic performance, is obtained by dividing the bullet’s expanded diameter by its initial, or pre-impact, diameter. To meet these comprehensive requirements, the Hornady .45ACP 230-grain XTP JHP +P and the Hornady 9mm 147-grain XTP JHP were selected since they are of the same structural design and source of manufacture and have similar sectional densities and subsonic impact velocities. The initial sectional density of the Hornady .45ACP 230-grain XTP JHP +P is 0.161181, which, at 96.73% of the initial sectional density of the Hornady 9mm 147-grain XTP JHP of 0.166634, makes both projectiles nearly identical to one another in that particular respect. The first commercially available JHP designed in 1990 to meet the F.B.I. test protocols, the Hornady XTP JHP is designed to offer moderately controlled-expansion to approximately 150% of its nominal projectile diameter meaning that both the Hornady .45ACP 230-grain XTP JHP +P and the Hornady 9mm 147-grain XTP JHP should produce similar expansion ratios and corresponding post-impact sectional densities if they do not fragment excessively and retain their most of their initial weight. In the tests presented in this article, both the Hornady .45ACP 230-grain XTP JHP +P and the Hornady 9mm 147-grain XTP JHP produced similar expansion ratios. In this case, the Hornady .45ACP 230-grain XTP JHP +P produced an expansion ratio of 1.319 while the Hornady 9mm 147-grain XTP JHP produced an expansion ratio of 1.389.

To correctly analyze these test results, we must look once more to the personnel incapacitation model produced within the Biophysics Division of the US Army Ballistic Research Laboratory at Aberdeen Proving Grounds in 1961 under the direction of Dr. A. J. Dziemian. A predictive personnel incapacitation model correlated against thousands of Wound Data Munitions Effectiveness Team (WDMET) wound data collected during the Vietnam War, the US Army Ballistic Research Laboratory’s Probability of Incapacitation model relies upon the incremental kinetic energy expenditure of a projectile over a penetration depth of 1 to 15 centimeters, or ΔE15, to predict the probability of incapacitation, P[I/H], for a random munition strike to the COM (e.g.: the thoracic or abdominal cavity) of an enemy combatant or an assailant. The US Army BRL incapacitation model takes the form of,

P[I/H] = [1 + e -(-a + b(logΔE15))]-1,

with the model’s coefficients, ‘a’ and ‘b’, being dependent upon the tactical situation with respect to either an “assault” or “defense” combatant response modality being modeled. Greater values of ΔE15 equate to greater strain energy storage in the tissues surrounding the expanded JHP’s path of travel increasing the likelihood of tissue damage and the probability of incapacitation. Using the US Army BRL P[I/H] model, the test data for both calibers is listed below along with the predicted Q-model penetration depth, total wound mass and volume, as well as the US Army BRL probability of incapacitation for up to three random consecutive projectile strikes to a combatant’s upper torso/abdomen within a 30-second time frame.

Hornady 9mm 147 gr. XTP JHP (90282)

Test Platform: Glock 17
Barrel Length: 4.49 inches
Test Media: water
Test Distance: 21 feet
Average Expanded Diameter: 0.493 inch
Expansion ratio: 1.389
Retained Weight: 146.0 grains (99.32%)
Impact Velocity: 998 feet per second

Predictive Terminal Performance Analysis
Maximum Penetration Depth: 19.34 inches
Wound Mass: 1.818 ounces
Wound Volume: 3.024 cubic inches

Cumulative Probability of Incapacitation within a 30-second time frame:
1st shot P[I/H]: 67.01%
2nd shot P[I/H]: 89.12%
3rd shot P[I/H]: 96.41%
ΔE15 : -182.062 foot-pounds

Hornady .45ACP 230 gr. XTP JHP +P (#9096)

Test Platform: HK USP45
Barrel Length: 4.41 inches
Test Media: water
Test Distance: 21 feet
Average Expanded Diameter: 0.595 inch
Expansion ratio: 1.319
Retained Weight: 229.6 grains (99.83%)
Impact Velocity: 916.7 feet per second

Predictive Terminal Performance Analysis
Maximum Penetration Depth: 18.91 inches
Wound Mass: 2.589 ounces
Wound Volume: 4.307 cubic inches

Cumulative Probability of Incapacitation within a 30-second time frame:
1st shot P[I/H]: 70.92%
2nd shot P[I/H]: 91.55%
3rd shot P[I/H]: 97.54%
ΔE15 : -235.036 foot pounds

Not surprisingly, the use of an expanding JHP improves the terminal performance of the .45ACP clearly exceeding the 9mm’s probability of incapacitation by nearly 4%. Moving within the relatively sedate subsonic velocity envelope of 800 — 925 feet per second, .45ACP projectiles weighing 230 grains suffer when FMJs are used since their ΔE15 depends upon the correct balance of velocity and cross-sectional expansion face area. Increasing the strain energy storage within surrounding tissues through the use of a larger cross-sectional expansion face area more effectively utilizes the low velocity (and low kinetic energy dissipation rate) available to the caliber. Use of a moderately expanding JHP, such as the Hornady 230-grain XTP JHP +P, at a slightly higher than normal velocity (+P), elevates the 1st-shot P[I/H] of the .45ACP 230-grain XTP JHP to a very respectable P[I/H] of 70.92%. Assuming consistent performance from the Hornady .45ACP 230-grain XTP JHP +P when used in the execution of the classic “double tap”—a time-proven tactical technique—brings the 2nd-shot P[I/H] of the .45ACP to a rather admirable 91.55% whereas executing a “double tap” with the Hornady 9mm 147-grain XTP JHP yields a 2nd-shot P[I/H] of 89.12%, for a difference in P[I/H] of 2.43%.

Obviously, with other JHP designs that demonstrate more aggressive expansion characteristics, an increase in P[I/H] for both calibers is likely, but carries with it the undesirable risk of reducing maximum penetration depth to a level below that indicated in Chapter 10 (page 91) of Quantitative Ammunition Selection; that is, a recommended penetration depth range of 14 — 18 inches. With the real possibility that a JHP, fired in self-defense from a service caliber pistol, may have to successfully defeat an assailant’s upraised hands, arms, a shoulder, or a thick layer of muscle or abdominal fat before entering the assailant’s COM (e.g.: the thoracic or abdominal cavity) to reach vital organs and neurological and vascular structures, the significant reduction of any projectile’s ability to penetrate 14 — 18 inches is highly inadvisable.

In conclusion, while both the 9mm and the .45ACP benefit significantly from the use of a moderately expanding JHP design, the improvement in the .45ACP’s lethality was much greater than that of the 9mm making the .45ACP the ‘winner’ in this case by a significant 3.91% margin in its 1st-shot P[I/H]. Since private US citizens carrying legally concealed firearms are not subject to the restrictions set forth under Declaration III of the Hague Convention of 1899 which requires signatory military combatants to use service ammunition of non-deforming designs (FMJs), it is highly recommended that regardless of the caliber being carried, the armed open or concealed carrier test and then select a premium-quality JHP suitable to their needs and desires for the purpose of defensive use.

Fortunately, the ability to test and determine which JHPs suit our individual needs is within reach for most of us. It is no longer necessary to shoot non-expanding and expanding ammunition designs into calibrated ordnance gelatin to measure maximum penetration depth, instantaneous velocity, wound cavity volume, crushed tissue mass and lethality. It is now possible to do so by simply firing test JHP ammunition into water and recovering it. Once the test bullet is recovered, all that is needed is to determine the average recovered expanded diameter, retained mass and impact velocity of the test bullet. With those three data, and using the equations set forth in Quantitative Ammunition Selection, it is a simple matter to obtain a valid predictive measure of all five of these important terminal performance variables; maximum penetration depth, instantaneous velocity, wound cavity volume, crushed tissue mass and lethality.

Quantitative Ammunition Selection is available domestically and internationally in hardcover, paperback, and eBook formats and may be purchased at www.quantitativeammunitionselection.com. Just select the appropriate link found on the lower portion of the webpage for the format that you want.