SSS.8.1.10 - Suppressed AR-15 Rifle Hazards - Otter Creek Labs OCM5 and OCM6 Silencer Hazard Map Brief
/Otter Creek Labs OCM5 and OCM6 Reflex Models on the M4A1 Mid-Gas 5.56x45mm 14.5-in Barrel Automatic AR15 Rifle - Hazard Maps
This Silencer Hazard Map Brief documents the free field blast overpressure hazards from the Otter Creek Labs OCM5 and OCM6 silencers fielded on the 14.5-in M4A1RIII AR-15 semiautomatic rifle firing M193 55gr 5.56 NATO ammunition, as evaluated in technical Report 6.213 and as tabulated in record numbers 7.1.240 and 7.1.241 in the Rankings, respectively.
The average Suppression Rating hazard contours at 1.6 m silencer end cap elevation from the instrumented blast test of the OCM5 silencer computed with the PEW-SOFT HD Blast Hazard Prediction Tool are shown in Figure 1. Hazard contours for the OCM6 silencer are shown in Figure 2. The Suppression Rating hazard scale is shown in Figure 3. Ground-truth anchored Suppression Ratings from the technical reports are annotated 1.0 m left of the end cap (SR_muzzle) and 6 inches right of the shooter’s right ear (SR_ear) in both figures. Computational parameters and blast overpressure hazard field observations are provided below.
8.1.10.1 PEW-SOFT HD Computational Model Parameters
PEW-SOFT HD code Version 2.2.6 Alpha was used.
Contour elevation is 1.6 m above grade. No reflecting surfaces, other than the ground, are present in the model.
Grid resolution is 0.076 m (3 in).
The average semiautomatic jet stability index sigma_sa of the OCM5 is 0.796. The OCM6 silencer has a lower jet stability index of 0.167.
8.1.10.2 Otter Creek Labs OCM5 and OCM6 Reflex Models Suppression Hazard Map Observations:
The Otter Creek Labs OCM silencer series are full size, 1.5-in diameter reflex hybrid designs. To compare overall system length with other non-reflex silencers, an equivalency that may be used is that the OCM silencers occupy the same resultant length envelope as a standard silencer and mount of approximately 6.9 inches past the barrel shoulder. The OCM5 model possesses lower early- and late-time flow rate than the OCM6 model; the OCM6 model may be considered "lower backpressure” than the OCM5. Blast load input into the silencers is relatively high amplitude from the 14.5-in rifle barrel. Blast load output from the silencers is highly controlled from the OCM5, with the OCM6 model producing a less stable jet and less control. The stability index of the OCM6 model drops due to its distal vent array.
Near-field severity forward of the operator is significantly less intense and less hazardous with the OCM5. The OCM6 produces safer near-field severity near the weapon operator. These hazard field differentials are driven by reduced ejection port blast hazards with the OCM6 model, along with its elevated muzzle blast hazards.
Both silencer models provide relatively consistent hazard fields after the first shot. Blowdown momentum is significantly controlled.
fig 1. Otter Creek Labs OCM5 14.5-in M4A1 AR-15 Free Field Hazard Map Produced by PEW-SOFT HD Blast Hazard Prediction Tool using PEW Science Test Data
fig 2. Otter Creek Labs OCM6 14.5-in M4A1 AR-15 Free Field Hazard Map Produced by PEW-SOFT HD Blast Hazard Prediction Tool using PEW Science Test Data
Fig 3. PEW Science Suppression Rating Scale
