When a jet aircraft tears through the air faster than the speed of sound, it creates a peculiar kind of noise that radiates out behind it in a conical pattern. People see the plane fly overhead, then later hear a "sonic boom" as the outer fringe of this giant invisible cone drags over the surface of the earth where they're standing.
The same thing happens on a smaller scale when a bullet travels faster than the speed of sound (about 1,100 feet per second, or fps). People standing downrange hear nothing as the bullet zips by; they then hear the sonic crack of the bullet, followed by the distant sound of the gunshot itself. Even if the muzzle blast of the gunshot is silenced, the sonic crack will still remain if the bullet is traveling faster than the speed of sound.
The easiest solution to the sonic crack problem is to use subsonic ammunition with a muzzle velocity rated lower than 1,100 fps. Some ammunition, such as .22 Short or .45 ACP usually falls well below the 1,100 fps sonic threshold. Other ammunition, such as .22 Long Rifle, is available in both supersonic and subsonic factory loads. Ammunition that is invariably supersonic, such as that fired by most centerfire rifles, usually must be specially loaded to subsonic velocity.
Supersonic ammunition can sometime be rendered subsonic by the silencer itself. Silencers constructed around perforated gun barrels absorb gases that are vented out through the perforations in the barrel. If enough gases are bled off this way, the velocity of the bullet can be reduced substantially. The velocity of a bullet can also be reduced if the bullet has to burrow through a series of wipes on its way out of the silencer.
Sometimes, though, lowering the velocity of the ammunition to avoid sonic crack just isn't feasible. In long-range sniping, for example, lowering the velocity of the bullet would rob it of the power it needs to reach and penetrate the target. In situations like this, simply suppressing the muzzle blast is all that can be done to make the sniper less conspicuous. Of course, if the sniper is far enough away, the velocity of the bullet may drop to subsonic levels before it reaches the target.
Nearly all the designs in this book require no more tools than a hacksaw, screwdriver, kitchen knife, modeling knife, scissors, can opener, and metal punch (or big nail). There are a few exceptions: one design requires a drill, one requires a chisel blade for the modeling knife, one requires a socket wrench, and one requires a means for cutting longitudinal slots in a short length of PVC tubing. (I used a hand-held Dremel Moto-Tool to do this. It could probably be done with a hand saw if the section of tubing is held in a vise.)
Adhesives—tapes and glues—are also used in many of these designs. Tapes used include masking, black vinyl, and metal repair tape in widths ranging from 3/4 inch to 2 inches. Glues used include epoxy, PVC cement, and anything suitable for permanent rubber-to-rubber and rubber-to-plastic bonds (like Goop). Liquid Steel and silicone sealant were used for a couple of fill applications.
The tapes are mostly used for "friction fitting"—wrapping just enough tape around one cylindrical object so that it will fit very tightly inside another cylindrical object. It takes a little practice to get it right: a mere half or quarter of a wrap might make the difference between a fit that's too loose or too tight and one that's just right. You may have to wrap, unwrap, and snip the tape several times. For added strength, wrap tape around the outside of the joint formed by the friction-fit components. If you don't plan on disassembling the silencer, you can go ahead and glue the friction fittings together.
Some components, however, may already fit together so snugly that wrapping even a single layer of tape around one will make it too wide to fit back inside the other. In cases like this, you'll need to use paint instead of tape. Spray a coat of primer on the component, let it dry, and try the fit. Repeat until a tight enough fit is obtained.
Some designs involve squeezing PVC bushings into snug-fitting rubber components. If the fit is too snug, you'll need to have some water-soluble gel on hand to use as a lubricant.
And finally, a variant of one design calls for the application of some lithium-based grease.
In order to avoid repetition, the tools and materials listed above won't be relisted along with the components that make up each silencer. We'll simply assume that you already have them all on hand.
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