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I might point out that the Arduino/msgeq7 system I suggested is capable of handling stereo inputs.
If the Arduino had two of the msgeq7 units, four microphones could be placed facing four different quadrants and if configured correctly, they might also be able to assess the general direction of the gunshot location. Of course, each microphone would have to be appropriately aimed and "coned" to only "listen" to one, each, of the quadrants.
Sound amplitudes should allow for this differentiation.