This second peak is called the “muzzle blast.” The third peak is the ground reflection of the muzzle blast, arriving to the microphone late in time after traveling to the ground and back. Because the distance between the air molecules is small enough such that the molecules can reach each other (the air can compress) faster than the bullet can push them out of the way, the molecules “pile up” in front of the bullet.Īfter the bullet exits the barrel, combustion products are released, forming the second peak in Fig 1. The first peak in Fig 1 is the pressure wave resulting from the compression of air as the subsonic bullet leaves the barrel the bullet is traveling at close to the speed of sound in air, but not quite at the speed of sound in air.
22LR waveform contains three major peaks. Viewing the gross waveforms, you may notice some immediate differences between the subsonic. Each of the waveforms shown in the figures is composed of 25,000 discrete points. PEW-SOFT records data at a rate of 1,000,000 samples per second (1 MHz). If you click (or tap) on each figure, a full-resolution version will be displayed. For reference, it takes a housefly approximately 3 ms to flap its wings, once. The time scale is kept constant between the figures, at a total of 25 ms. The horizontal axis in each figure displays units of time in milliseconds, while the vertical axis displays units of pressure in pascals. 308 Winchester (.308WIN) centerfire from a 20 inch barrel (Fig 2). 22 Long Rifle (.22LR) rimfire from a 16 inch barrel (Fig 1) and supersonic.
īelow are two measured free-field pressure waveforms both measured on the same day, at the same location (1.0 m left of the weapon muzzle, 1.6 m above ground level, over 10 m away from any reflecting surfaces). These two regions are not necessarily the true extreme ends of the spectrum, but practical regions of which many people familiar with firearms are aware: subsonic rimfire and supersonic centerfire, both fired out of bolt action rifles. Let’s take a look at two regions of the unsuppressed firearm loudness spectrum. Before there were silencers, there were guns.
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