[MaciekA]

You should use a computer to do the recording, with a proper mic and at a decent sampling rate. The problem with using these cheesy sound level apps is that just like those analog Amperage meters , they miss out on the spikes and detail. You might end up concluding that a given AEG is much louder on account of its gear spin-up or your phone's crappy microphone when in fact the overall report from the muzzle is quiet.