Acoustic bullet detection and measurement

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Title Acoustic bullet detection and measurement
Summary Measure speed and direction of a supersonic rifle bullet with acoustic sensors
Keywords electronics, physics, computer engineering
TimeFrame spring
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Prerequisites electronics, computer engineering
Author Stefan Axelsson
Supervisor Stefan Axelsson, Pererik Andreasson
Level Flexible
Status Open

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Measurement of bullet speed and direction of travel is important in many situations. From speed measurement when developing rifle ammunition (to achieve accuracy and ensure the round is legal to hunt with) to ballistic measurement of guns shots in crimes (or war zones).

Most simple chronographs today use optical sensors, but these have the drawback that the bullet has to pass through a very well defined measurement zone (on the order of 20x20cm). This means that down range (i.e. close to the target) measurements are not possible as the risk of missing (and shooting the measurement device) are too great. This is problematic in that Swedish legislation specify minimum energy for hunting ammunition at 100 meters, not the muzzle.

However, the bow shock wave from a supersonic bullet is of very short duration and easy to detect. Hence the careful placement of microphones somewhere along the bullet path should lead to an accurate measure of bullet flight, both speed and direction. (Measuring where the bullet hit on a paper target should be possible as well, given the proper geometry of the microphones).

So this project entails developing a chronograph that is highly accurate (better than one part per thousand) and that can be more freely placed down range, and report speed (and placement/direction if possible) to the shooter.

Sponsorship and guidance from the hunting/gun shop just across the parking lot from the school has been secured in the form of an experienced former police officer with access to rifles and the local range. (Thus also ensuring the legality and safety of the project).