Page 92 - JSOM Winter 2018

barrel length was inconsistent and largely inconsequential to FIGURE 1 Comparison of muzzle brake type and shooter
shooter OP. OP increased, then decreased, as longer barrels overpressure.
were tested.

TABLE 4 Study 2: Effects of Barrel Length
Impulse,
Barrel Length OP, mean mean (SD)
(inches) (SD), psi 95% CI (m × psi) No.
24 3.62 (0.30) 2.93, 4.51 2.16 (0.73) 9
26 3.38 (0.23) 2.71, 4.14 2.19 (1.37) 8
27 3.82 (0.42) 2.93, 5.56 2.53 (1.38) 16
28 5.37 (0.08) 4.98, 5.87 1.69 (1.18) 4
29 4.86 (0.72) 2.64, 7.26 2.63 (1.88) 50
CI, confidence interval; OP, overpressure; SD, standard deviation.

To determine which muzzle devices were best for different PSI, pounds per square inch.
operational needs, muzzle devices were isolated and investi-
gated. The data are listed in Table 5. Ported brakes that do
not direct the blast to the rear to help mitigate felt recoil are muzzle brakes that help control recoil. Attention to selecting
a good option for OP mitigation, followed by not using any firing positions, particularly those that put shooters atop rigid
type of muzzle device (target crown). Slanted brakes are good metal surfaces or from within vehicles, should be scrutinized
at helping reduce the amount of recoil the shooter feels, but before use to ensure they are necessary for mission param-
they come at the expense of increasing experienced OP on the eters. Firing from within vehicles to simulate a vehicle hide
operator. This does not mean they should not be used, only and from atop rigid structures should be minimized when rea-
that this limitation should be understood. Shooter efforts to sonably possible within training environments, because they
mitigate OP are better spent on careful selection of a muzzle seem to considerably increase OP and impulse exposure. It is
device rather than increasing barrel length, because no reason- reasonable to assume that minimal firing from within vehicles
able barrel length can overcome the increase in exposure from and atop rigid surfaces for verification of shooting platform
redirected blast. and concealment is all that is necessary for shooters, because
firing from other positions provides sufficiently transferrable
TABLE 5: Study 2: Effects of Muzzle Device skills to not degrade performance. Overwhelmingly, the use of
Impulse, suppressors on .50-caliber rifles in vehicle hides can be an ef-
OP, mean mean (SD) fective means at mitigating OP and still allow for operational
Muzzle Device (SD), psi 95% CI (m × psi) No. readiness and use. Use of slanted muzzle brakes that mitigate
No brake; recoil by directing blast toward the operator increase OP but
OT and IT 3.52 (0.74) 2.64, 5.56 2.41 (1.05) 27 greatly improve capacity for firing multiple follow-up shots
excluded and may not be readily avoidable if that ability is required (but
Ported muzzle see the exception discussed later)). As such, it is not prudent
brake; OT and 3.08 (0.30) 2.71, 3.38 1.38 (.98) 6
IT excluded to eliminate the chevron- or arrowhead-style brakes from con-
45° slant sideration; instead, it is advisable that trainings minimize their
brake; OT and 5.16 (0.87) 3.04, 6.83 2.26 (0.99) 42 use where possible.
IT excluded
No brake, OT 4.25 (0.61) 3.03, 4.77 3.46 (1.06) 6 Evaluation of Suppressor Use
and IT only Additional, limited testing was done with suppressors during
Ported muzzle study 2. Limited data (n = 23 shots with suppressors) from
brake, OT and — — — — the study found a 92% reduction in OP readings as compared
IT only with no muzzle device, a 120% reduction in measured OP as
45° slant compared to the 4° muzzle brake, and a 49% reduction in
brake, OT and 5.69 (1.49) 3.02, 7.28 3.39 (0.97) 8 measured OP compared with a flash hider. Direct compari-
IT only
—, not measured; CI, confidence interval; IT, inside BearCat; OP, sons could not be made to the other data, because the sen-
overpressure; OT, atop BearCat; SD, standard deviation. sors used for the rest of the analysis with the best incident
orientation did not trigger for any of the 23 shots. As such,
we compared a less desirable sensor (i.e., wrist) with other
Conclusions: Study 2 wrist sensors to determine the cited data. We believe this is not
Within constraints and availability to the operator, as deter- representative of the incident blast received; therefore, we do
mined by mission parameters, barrel length had an incon- not report those values. However, we do feel the readings are
sistent and inconsequential impact on shooter OP. Muzzle proportionally equivalent, which is why we report them as a
devices, however, seem to influence OP consistently, with change in percentage.
brakes that mitigate recoil increasing shooter OP over all other
brakes tested (Figure 1). We evaluated other shoulder sensors across different conditions
and found them to respond proportionally to the wrist, further
Emphasis on OP mitigation should focus on muzzle device, supporting this method. Results show substantial promise for
with additional scrutiny applied to the selection of slanted suppressor use as a meaningful way to lower experienced OP

90 | JSOM Volume 18, Edition 4 / Winter 2018