Page 89 - JSOM Winter 2018

Shooter-Experienced Blast Overpressure
in .50-Caliber Rifles

2
1
Mark Lang ; Gary H. Kamimori, PhD ; Anthony Misistia, MS ; Christina R. LaValle, MS ;
2
2
2
A. N. Ramos ; M. Y. Ghebremedhin, MS ; Michael J. Egnoto, PhD *
2
2

ABSTRACT
Background: Increasingly, military and law enforcement are capability. The blast, or the forces that result from firing the
using .50-caliber rifles for conflict resolution involving bar- .50-caliber rifle, strikes the operator with enough energy to
ricades, armor, vehicles, and situations that require increased warrant implementing strategies that minimize shooter risks
kinetic energy. Consequences to the shooter resulting from that may result from exposure.
the blast produced while firing these rifles remain unknown.
We measured blast overpressure (OP) and impulse across var- The effects of blast on the operator of weapon systems have
2
ious positions, environments, and weapon configurations to been the subject of research for over 50 years. Current re-
evaluate blast exposures to shooters. Methods: Two separate, search suggests some individuals may experience deleteri-
multiday, .50-caliber rifle training courses were evaluated to ous effects that may affect readiness after repeated exposure
3–5
understand the blast exposure profile received from various to blast and could experience negative consequences to
tactical training scenarios, such as different firing positions health. This presents a two-fold problem: Improper training
6,7
(e.g., standing, prone, seated, kneeling) and locations (e.g., in- not only could jeopardize shooters’ ability to perform their
side and atop vehicles, inside buildings, on hard/soft surfaces) duties in critical situations but also pose a risk to their long
across a variety of .50-caliber rifles with various barrel lengths, term health unnecessarily.
muzzle devices, and ammunition. Blackbox Biometrics, Gen-
eration 6, gauges were placed on operators to measure inci- The purpose of this research was to characterize OP exposure
dent blast exposure. A total of 444 rounds fired from various associated with firing the .50-caliber rifle during training and
.50-caliber rifles were evaluated to determine what OP was to understand what components of the weapon have the most
received by 32 different shooters. Results: Our findings indi- impact on operator exposure. The peak blast OP as well as im-
cate OPs >4 psi are common and that muzzle devices are crit- pulse, which is the total force exerted on an object from an OP,
ical to blast exposure. Shooting positions closer to the ground were measured in conjunction during two separate .50-caliber
experienced higher OP and impulse than did other positions. rifle training courses. These blast characteristics were mea-
Suppressors mitigated blast effects well. Conclusion: When sured across different barrel lengths, muzzle devices (including
resources and operational parameters allow, suppressors are suppressors), shooting positions, and shooting locations. Mea-
recommended, as are positions that move the shooter farther surements were made during realistic training environments
from reflective surfaces (standing preferred) to effectively re- that mimic the operational environments likely to be encoun-
duce blast exposure. These shooter positions may require the tered by shooters. It was hypothesized that even though many
use of supplemental rifle rests/tripods to provide sufficiently .50-caliber rifles exceed current military doctrine for blast ex-
stable firing platforms from the standing position. posure (≥4 psi), reasonable changes in environment, weapon
system configuration, or shooting position can help mitigate
Keywords: risk evaluation; risk mitigation; work engagement; shooter exposure. The 4-psi threshold for OP originates from
occupational stress; wearable electronic devices; interdisci- a collection of reports supporting atomic weapon develop-
plinary research; rifle; overpressure ment, which noted that an increased probability in the rupture
8
of the tympanic membrane was possible at OPs >4 psi. Hear-
9
ing damage has been linked to traumatic brain injury, and so
Introduction the 4-psi threshold has carried over as a proxy that indicates,
to some extent, that the 4-psi threshold, in accordance with
The effects of overpressure (OP) exposure from weapon sys- current research and understanding, represents a best known
tems (e.g., .50-caliber rifles, flash bangs) are receiving growing point where the potential for neurocognitive perturbation may
attention from the scientific community. In addition to broad occur. Additional information on the 4-psi threshold can be
military applications, the US law enforcement community is found in SWO 60-AA Vol 1 REV. 9—Demolitions Technical
seeing a significant emergence of “light .50” rifle systems. As Manual, and FM 3-34.214 (FM 5-250)—US Army Explosives
1
more law enforcement agency Special Weapons and Tactics and Demolition.
teams, military, and other relevant operators expand their ca-
pabilities to include .50-caliber rifles, training doctrines need All OP measurements in this article are in pounds per square
to evolve to minimize risks to shooters without compromising inch and represent incident OP. This article is organized as
*Correspondence to Michael J. Egnoto, PhD, 503 Robert Grant Ave, GW51, Silver Spring, MD 20910; or Michael.J.Egnoto.CTR@mail.mil
2
1 SR CPL Lang is at TacFlow Academy, Phoenix, AZ. Dr Kamimori, Mr Misistia, Ms LaValle, A.N. Ramos, M.Y. Ghebremedhin, and Dr Egnoto
are at Walter Reed Army Institute of Research, Silver Spring, MD.
87