When a bullet leaves the barrel of a gun, it is followed by a mushrooming cloud of hot, burning, expanding gases. When these gases collide with the cooler surrounding air, a loud blast is produced. If these hot gases can be contained and delayed for just a split second, it slows them down and cools them down just enough that they make much less racket when they finally escape into the atmosphere. The silencer is the device that regulates the release of these gases. It may embody any of the following features:
1) Expansion Chamber—An enclosed space that briefly contains the gases before they follow the bullet out of the silencer.
2) Baffles—A series of partitions through which the bullet must pass. The simplest baffles are just washers mounted at intervals in a tube. Baffles split the silencer up into a bunch of little expansion chambers.
3) Perforated Tube—A slotted or drilled tube that makes up the core of some silencers. The gases following the bullet down the tube are vented out through the perforations and absorbed by diffusing material surrounding the tube.
4) Wipe—A relatively thick rubber disk penetrated by the bullet. The gases following the bullet are sealed off behind it as the bullet burrows its way through the wipe.
5) Packed Tube—Wire mesh washers or the like packed solid in the main silencer tube. The gases following the bullet are forced into the tiny spaces in the packed material.
Nearly all the silencers in this book work on the "expansion chamber" principle because rigging a hollow container onto the end of a gun is such a relatively simple procedure. These containers, however, may be lined, stuffed, or covered with sound-damp-ening materials to enhance their efficacy.
A number of designs use wipes made from a variety of objects. One design, a sponge stuffed into a plastic shell, is actually nothing but one big wipe.
A couple of designs involving containers arranged end to end incorporate the baffle principle: the bullet must pass through a little hole in the end of one container in order to enter the adjoining container.
Three designs show silencer tubes that can easily accommodate simple baffles or packed washers.
The only basic silencer principle not shown or suggested in this book is the perforated tube. It requires a lot of slotting or drilling, very close tolerances, and near perfect alignment that is very difficult to achieve.
With certain guns, not all the gases exit the muzzle; some of the gases end up escaping from around the rear of the barrel. When these gases collide with the cooler surrounding air, they too produce noise. Putting a silencer on the front of the barrel won't suppress noise coming from the rear of the barrel.
Revolvers have a gap between the cylinder and the barrel that allows gases to escape. The whisper-quiet silenced revolvers seen on TV and in the movies are a myth; the blast from the cylinder gap would make quite a racket. (Unless, of course, the revolver were an M1895 Nagant; this unique weapon incorporates mechanical features that seal the gap between the cylinder and the barrel every time the hammer is cocked.)
Automatic and semiautomatic weapons have bolts or slides that fly back with each shot, extract and eject the spent cartridge, then slam forward and chamber the next round. If there are burning gases still in the barrel when the breech opens up during this process, these gases will escape from the rear of the barrel.
Making sure the breech stays closed eliminates this problem. Special slide locks can be installed to accomplish this, or the shooter can simply brace the heel of his hand against the back of the slide or bolt. Another strategy is to use low-power ammunition that doesn't have the energy to push the slide or bolt back. (Low-power ammunition is quieter, too, so there's less noise to silence.)
The interaction of the moving parts of a gun produces noise apart from the actual sound of the weapon's discharge. For example, just racking back the slide or bolt of an automatic or semiautomatic weapon and letting it slam forward can make quite a bit of clatter in and of itself. When the weapon cycles during firing, that noise is still going to be there, regardless of how efficient a silencer might be screwed onto the barrel. The problem is even more acute in fully automatic weapons, where a steel bolt in a steel receiver might slam back and forth a dozen or more times in a single second.
Eliminating the slamming of the bolt or slide can be accomplished by the same remedies for breech blast: manually holding the bolt or slide down, mechanically locking the slide, or using low-power ammunition.
Sometimes, as with the Colt .45, the weight of a heavy silencer on the barrel can eliminate the movement of the slide. This occurs because of the way the barrel and the slide work together when the weapon is fired. Ordinarily, the recoil that pushes the slide back also pulls the barrel back a short distance because the slide is locked onto the barrel by several interlocking grooves. The back of the barrel then cams slightly downward, disengaging these interlocking grooves, and the freed slide flies all the way back. (Keeping the barrel and slide locked together for a short time gives the bullet time to clear the barrel before the breech opens up, thus eliminating or minimizing breech blast.) When a heavy enough silencer is hung on the end of the barrel, the slide can't pull the barrel back far enough for the interlocking grooves to disengage and free the slide.
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