Soft Points and Water Testing

[Unobtanium]

It is my opinion that testing soft-point rifle ammunition (or pistol) in water jugs is "a difficult test" on the ammo at the low end of the velocity scale. Water is less dense than anything you will be trying to kill with the projectile. With a hollowpoint, it is "cheating" and will result in either false indication of expansion viability at low velocity, or false failure at high velocity due to over-expansion, as water fills the nose better than anything you will be killing.

Are these presumptions/opinions correct, that water jug testing will require MORE velocity from a soft point, and LESS from a hollowpoint, when testing rifle ammunition, to initiate expansion?

[JCN]

Paging @the Schwartz to the courtesy phone…

[the Schwartz]

It is my opinion that testing soft-point rifle ammunition (or pistol) in water jugs is "a difficult test" on the ammo at the low end of the velocity scale. Water is less dense than anything you will be trying to kill with the projectile. With a hollowpoint, it is "cheating" and will result in either false indication of expansion viability at low velocity, or false failure at high velocity due to over-expansion, as water fills the nose better than anything you will be killing.

Are these presumptions/opinions correct, that water jug testing will require MORE velocity from a soft point, and LESS from a hollowpoint, when testing rifle ammunition, to initiate expansion?

The density of water, 0.998 g/cm³ @ 20°C, falls squarely within the range of densities (0.950 ≥ ρ_x ≤ 1.065 g/cm³) occurring in mammalian (human) soft tissues, with adipose tissue being at the low end of the range (0.950) and skeletal muscle at the upper end (1.065) in Basics of Biomedical Ultrasound for Engineers, Azhari H (2010).

According to Empirical relationships between acoustic parameters in human soft tissues, Acoustical Society of America, Mast TD, (2000), the aggregate density of the human body is 1.043 ± 0.042 g/cm³.

Water tends to very slightly overdrive projectile expansion so, depending upon the specific alloy(s) involved in the projectile's construction, a correspondingly lower expansion threshold velocity for certain projectiles may exist in such instances.

A comprehensive approach to evaluating the equivalence of soft tissue simulants to mammalian soft tissues is the use of an EOS (equation of state) that allows the comparison of the physical and acoustic properties of soft tissue simulants. These equations take the form of—

U_S = c_o + Su_P

—where the equation’s intercept value, c_o, is the medium's temperature-dependent internal sonic velocity (in km·s^-1), the equation’s slope, S, is a first-order derivative of the medium’s bulk modulus (K) expressed in N·m^-2, u_P is particle velocity (in km·s^-1), and U_S is the shock Hugoniot velocity (in km·s^-1) of the wave front propagated through the medium ahead of the projectile.

Human Adipose Tissue: U_S = 1.465 + 1.781u_P

H₂O: U_S = 1.483 + 1.867u_P

Skeletal Muscle: U_S = 1.547 + 2.136u_P

10% Type 250-A ordnance gelatin: U_S = 1.513 + 2.024u_P

As can be seen, the slopes and intercept values of all four EOS are very close to one another indicating sufficient similitude amongst all four mediums.

Short answer: Water is an acceptable soft tissue simulant.

[Unobtanium]

The density of water, 0.998 g/cm³ @ 20°C, falls squarely within the range of densities (0.950 ≥ ρ_x ≤ 1.065 g/cm³) occurring in mammalian (human) soft tissues, with adipose tissue being at the low end of the range (0.950) and skeletal muscle at the upper end (1.065) in Basics of Biomedical Ultrasound for Engineers, Azhari H (2010).

According to Empirical relationships between acoustic parameters in human soft tissues, Acoustical Society of America, Mast TD, (2000), the aggregate density of the human body is 1.043 ± 0.042 g/cm³.

Water tends to very slightly overdrive projectile expansion so, depending upon the specific alloy(s) involved in the projectile's construction, a correspondingly lower expansion threshold velocity for certain projectiles may exist in such instances.

A comprehensive approach to evaluating the equivalence of soft tissue simulants to mammalian soft tissues is the use of an EOS (equation of state) that allows the comparison of the physical and acoustic properties of soft tissue simulants. These equations take the form of—

U_S = c_o + Su_P

—where the equation’s intercept value, c_o, is the medium's temperature-dependent internal sonic velocity (in km·s^-1), the equation’s slope, S, is a first-order derivative of the medium’s bulk modulus (K) expressed in N·m^-2, u_P is particle velocity (in km·s^-1), and U_S is the shock Hugoniot velocity (in km·s^-1) of the wave front propagated through the medium ahead of the projectile.

Human Adipose Tissue: U_S = 1.465 + 1.781u_P

H₂O: U_S = 1.483 + 1.867u_P

Skeletal Muscle: U_S = 1.547 + 2.136u_P

10% Type 250-A ordnance gelatin: U_S = 1.513 + 2.024u_P

As can be seen, the slopes and intercept values of all four EOS are very close to one another indicating sufficient similitude amongst all four mediums.

Short answer: Water is an acceptable soft tissue simulant.

Does it over-drive soft points, or just hollow points? Or both?

[the Schwartz]

Does it over-drive soft points, or just hollow points? Or both?

Both.

[358156hp]

What effect does the layers of plastic containers (bottles) have on the results? I have long scoffed at water jug tests being skewed by the presence of the layers of plastic, and their effect on water caused by being restricted in plastic jugs until they reach their bursting point. I have scoffed even harder at tests that involved the use of jugs of varying construction materials. I recently saw one where the tester had water jugs, milk jug, fruit juice jugs, and other containers of varying constructions. Is this less of a factor than I've made it out to be? The difference seems to me to be comparable to that of apples and elephants.

I am genuine interested, I'm too tired to troll anyone tonight.

[Shawn Dodson]

Water-filled cardboard half-gallon milk cartons is the only verified and validated "milk carton" test equipment I'm aware of. I'm unaware of anyone comparing water-filled plastic milk or juice containers to properly prepared and calibrated Type 250A ordnance gelatin.

In the final issue of the IWBA's Wound Ballistics Review (Volume 5, Number 2), Fackler suggested using a single water-filled milk carton to cause the bullet to expand, with a box filled with polyester pillow batting to catch the bullet undamaged. Then one could use the formulae in MacPherson's book, Bullet Penetration" to determine penetration depth.

A water filled 55 gallon barrel might work, depending on the length of the bullet's "wound track".

FWIW, I've shot pistol bullets into my backyard swimming pool to see how they perform.

[the Schwartz]

What effect does the layers of plastic containers (bottles) have on the results? I have long scoffed at water jug tests being skewed by the presence of the layers of plastic, and their effect on water caused by being restricted in plastic jugs until they reach their bursting point. I have scoffed even harder at tests that involved the use of jugs of varying construction materials. I recently saw one where the tester had water jugs, milk jug, fruit juice jugs, and other containers of varying constructions. Is this less of a factor than I've made it out to be? The difference seems to me to be comparable to that of apples and elephants.

I am genuine interested, I'm too tired to troll anyone tonight.

You are correct. The strength and elasticity of the different materials used as you describe can have an effect upon the behavior of the bullets being tested.

From a strict engineering perspective, barrier materials with higher strength and elasticity can, and will, contribute to increased bullet deformation and an uncharacteristic loss of mass driven by excessive erosion and shear forces as is case with the various types of polymer found in beverage container manufacture.

Minimum dynamic puncture energy (E_p, measured in Joules per square centimeter, J/cm²), ultimate strength (UTS, in MPa), and failure strain (ε, as a % of initial sample length), are the relevant parameters.

To begin with, the ''container'' that surrounds the human body that bullets must pass through is skin, which according to Bir, C. A., Stewart S. J., Wilhelm, M., Skin Penetration Assessment of Less Lethal Kinetic Energy Munitions, Journal of Forensic Sciences, Vol. 50, No. 6, 1426-1429, 2005, has an E_p of 38.365 ± 14.375 J/cm², a UTS of 28.60 ± 8.40 MPa, and an ε of 54.00 ± 17.00%, meaning that it is rather elastic and fairly strong.

Compered to human skin, the polymers most commonly found in beverage containers are polyethylene terephthalate (PET), high density polyethylene (HDPE), and low-density polyethylene (LDPE) which have the respective elasticity/strength profiles;

PET: E_p of 31.00 ± 3.00 J/cm², a UTS of 57.00 ± 3.00 MPa, ε of 115.00 ± 5.00%

HDPE: E_p of 103.75 ± 72.55 J/cm², a UTS of 27.00 ± 16.00 MPa, ε of 800 ± 150%

LDPE: E_p of 3.60 ± 3.40 J/cm², a UTS of 10.19 ± 0.81 MPa, ε of 350 ± 250%

None of these materials match the elasticity/strength profile of human skin very well, so finding a suitable candidate material that introduces 'zero' effects to the process is the best solution since skin shored up against the body itself during projectile entry does not alter the expansion of bullets. That candidate material is the coated paperboard found in ½-gallon food-grade coated paperboard cartons with areal densities in the 500 g/m² range.

Paperboard, food-grade, coated; 500 g/m²: E_p of 1.355 ± 0.050 J/cm², a UTS of 0.475 ± 0.175 MPa, ε of 3.60 ± 1.10%

Paperboard has an E_p, UTS, and ε that is a small fraction of the materials above reducing greatly the introduction of potentially confounding factors into the empirical process.

At this time, if using a Fackler box containing sealed 1-gallon storage bags filled with water is inconvenient, the preferred test container is water-filled ½-gallon 3.75''D x 3.75''W x 9.00''H paperboard cartons that are commonly found in the grocery store milk and juice sections. The nice thing about using paperboard cartons is that arranging them ''sideways'' allows the seals at the top of the carton to be used to align them and their flat bottoms make setting up very easy.

Estimates of maximum soft-tissue (or 10% ordnance gelatin) penetration depth for bullets recovered in either manner may be obtained by using MacPherson's WTI equation or the Q-model found in Quantitative Ammunition Selection, both of which are modified Poncelet forms.

[Glock17JHP]

Water-filled cardboard half-gallon milk cartons is the only verified and validated "milk carton" test equipment I'm aware of. I'm unaware of anyone comparing water-filled plastic milk or juice containers to properly prepared and calibrated Type 250A ordnance gelatin.

In the final issue of the IWBA's Wound Ballistics Review (Volume 5, Number 2), Fackler suggested using a single water-filled milk carton to cause the bullet to expand, with a box filled with polyester pillow batting to catch the bullet undamaged. Then one could use the formulae in MacPherson's book, Bullet Penetration" to determine penetration depth.

A water filled 55 gallon barrel might work, depending on the length of the bullet's "wound track".

FWIW, I've shot pistol bullets into my backyard swimming pool to see how they perform.

Shawn,
For my water-testing while in the IWBA I had a tank fabricated from 2 55-gallon drums, 1 compete drum and a section of a 2nd drum. IIRC, the tank was about 90 gallons, because my calculations before fabrication told me I needed more water depth than just one drum would provide. I still have my testing tank if anyone wants info about it.
-Ron Jones.

[Shawn Dodson]

Shawn,
For my water-testing while in the IWBA I had a tank fabricated from 2 55-gallon drums, 1 compete drum and a section of a 2nd drum. IIRC, the tank was about 90 gallons, because my calculations before fabrication told me I needed more water depth than just one drum would provide. I still have my testing tank if anyone wants info about it.
-Ron Jones.

I saw the photo of your test setup in WBR when your article was published. Very nice!