Propelling the bullet via compressed air there is no explosion. Specially to your attention, Lestrade, and also the bullets which fit Never before had the opportunity of handling it. For years I have been aware of its existence, though I have German mechanic, who constructed it to the order of the late Professor вЂњAn admirable and unique weapon,вЂќ said he, Holmes had picked up the powerful air-gun from the floor and wasД®xamining its mechanism. After he is captured Holmes looks over the gun. In The Adventure of the Empty House, Colonel Adair attempts to assassinate Holmes using a special air gun. Use an electronic primer to eliminate the noise from the striker mechanism, and integrate suppressor baffles into the barrel to eliminate any noise produced as the bullet scrapes by, and there you have it- a completely silent firearm. While there might be some noise from the striker, at most it is a 'click' rather than the loud bark of even a suppressed and subsonic conventional round. The only noise in the action comes from the internal striker system, and the mechanical friction between the bullet and barrel.ДЄs long as the bullet is subsonic (and in this design, it is) there will be no sonic boom as it passes. When it reaches the end of its stroke, the piston seals on the front of the cartridge, preventing any noise or gases from escaping. When propelled by the gunpowder charge at the rear, the piston rams the bullet forward, propelling it down the barrel. If you look in the cutaway cartridges, you will see this piston behind the bullet. This firearm, like the others in its family, uses a unique piston-driven cartridge. All magnets used are functionally 5 times stronger, a strong dose of handwavium included). The technology of the time is similar to the present time, but there are advances in magnetic technology (they have far more powerful magnets as they have super compressed magnetic material and have aligned it in the same direction. It should be silent within Earth's atmosphere, regardless of the weather. It should be able to survive more than one shot, at a minimum firing rate of three times per minute. This should be a reliable weapon which can reliably kill a human at 200 meters, regardless of whatever is shot or projected. The measuring device we'll use is a human hearing the firing of the gun. Even something that used magnets to propel the bullet would have something keeping the bullet back, and that may grind against other metal in the gun.ДЄny sound produced must not be within the range of human hearing (20Hz to 20kHz) sound produced outside of that range is fine. The firing mechanism would most likely produce sound.The bullet may grind against the barrel of the gun, creating a grinding sound one could hear.Most bullets move quick enough to make a whistling sound, but I may be incorrect in that regard.

Is a gun which produces no sounds within the human range of hearing possible? I know of a couple issues:

Quiet the sound of a gunshot