Shooting an air rifle at 1400 feet per second does not produce a sonic boom because the shooter is positioned within the shockwave cone created by the bullet, preventing them from hearing it. The noticeable crack heard when firing is primarily due to the explosion at the barrel, not the bullet's sonic boom. Subsonic ammunition avoids this crack because it travels slower than the speed of sound. The sonic boom's characteristics, such as pitch, depend on the object's shape and speed, with smaller, faster objects typically producing higher-pitched sounds. Overall, the phenomenon of sonic booms is influenced by various factors, including the bullet's speed and the surrounding environment.