how to build a suppresor?

Answer 1

Supressors or silencers, are LEGAL in many areas of the US today (arizona, being one).
Construction can be rather simple. The lengthy answer posted above describes what one is, but does little to help you build one.
depending on the power of your cartridge, you should attempt to have an outer tube of roughly 3 times the outer diameter of the barrell of the gun.
washers drilled to .05 inch larger than the bullet (THIS must be precisely centered) welded to either end. Internally you may use several methods
1. the close stacked method. This uses a series of hard and soft spacers, typically made of steel washers and 3M green scrubbing pad-type material (the kind used for scouring pots and pads) packed alternating materials until the tube is full.
a nut is centered and welded onto one of the end washers.
This is a heavy and not completely silent supressor, but it is cheap and easy to build
the second type follows current auto and motorcycle muffler design.
again starting with an outer tube and end washers correctly drilled.
inside there is a steel screen or perforated sheet of steel rolled in a diameter slightly larger than the bullet, so as not to contact the bullet. the space between the screen and the outer tube is stuffed with either fiberglass or steel wool. If using steel wool, it is recommended to use various grades to help absorb a wider range of frequencies.
This type of supressor is musch lighter and efficient and lasts a VERY long time. the drawback is that it takes a much more skilled hand to fabricate.

ENJOY!

Answer 2

Suppressor design and construction
The suppressor is typically a hollow cylindrical piece of machined metal that attaches to the muzzle of the pistol or rifle. Some others are designed as an integral part of the weapon, and may include an expansion chamber that partially surrounds the barrel (These are often called "telescoping" designs, a reference to old-fashioned collapsing telescopes). The outer casing of the supressor is typically referred to as the can.

The suppressor reduces noise by allowing the rapidly expanding gasses from the detonation of the round to be briefly diverted or trapped inside a series of hollow chambers. The trapped gas can cool and expand, reducing the pressure and velocity as it exits the supressor. The divisions between these chambers are called baffles or wipes (see below). There are typically at least 4 and up to perhaps 15 chambers in a supressor, depending on intended use and design details. The engineering design of modern suppressors is analogous mathematically to the design of electrical filters, and many of the same design techniques may be used to design either.

Often, a single, larger expansion chamber is right at the barrel's muzzle, which allows the propellant gas to expand considerably and slow down before most of it begins to encounter the shaped baffles or wipes section of the supressor.

Suppressors vary greatly in size and efficiency. One disposable type developed in the 1980s by the US Navy for 9 mm pistols is 150 x 45 mm (5.9 x 1.77 in) and is good for six shots with standard ammunition or up to thirty with low-powered, subsonic ammunition. The British Sterling suppressor is 350 mm (13.78 in) long and 75 mm (2.95 in) in diameter and will work effectively for hundreds of shots with standard ammunition.


Baffles
Baffles are inner walls which separate chambers and are designed not to touch the bullet as it passes the baffle, typically by having a circular hole at least 0.05 inch / 1 mm larger than the bullet caliber. Baffles are typically metal, either machined solid shapes or stamped sheet metal. A few suppressors for small calibers (such as .22 LR) have successfully used plastic baffles.

Baffles are separated by spacers, which keep them aligned at the intended distance apart inside the supressor can. Some baffles are manufactured in one piece with their spacers being part of the baffle.

Modern baffles are usually carefully shaped to divert the gun propellant gases effectively into the chambers. This shaping can be a slanted flat surface, canted at an angle to the bore, or a conical or otherwise curved surface. One popular technique is to have alternating slanted surfaces, angled to one side, then the other, back to the first side, and so on through the stack of baffles.

Some supressors use a single, helical baffle which winds around the bullet hole in a single piece throughout the baffle length.


Baffle lifetime
Baffles usually last for a significant number of firings. They are heated and slightly eroded by the gun's propellant gas rushing past them, and over time erosion will damage the supressor. Damage happens slowly with steel baffles and slow single shot firing, happens rapidly with steel baffles and fully automatic firing, and happens extremely rapidly with aluminum baffles and rapid fire. Some modern suppressors having steel baffles can be fired for extended periods of time on fully automatic without damage, and other modern suppressors use high temperature alloys such as inconel or titanium for longer life and reliable service with automatic fire. The highest quality rifle suppressors available today have a service life of greater than 30,000 rounds.


Wipes
Wipes are inner dividers intended to touch the bullet as it passes. Wipes are typically rubber or plastic or foam. They may have a hole drilled in them before use, or a pattern cut through at the point the bullet will strike them, or they may simply use the bullet's energy to punch a hole.

Wipes typically last for a small number of firings, perhaps no more than 5 before their performance is significantly degraded.

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Liners
Various materials may be used to line the chambers and dissipate or cool the gases; these include metal mesh and steel wool. These are more effective than empty chambers, but less effective than wet designs (see below). Steel wool degrades very rapidly (ten shots or so); metal mesh may last for hundreds or thousands of shots of semi-automatic fire, or somewhat less for fully automatic fire.

Very effective suppressors either take large total suppressor volume, moderately large volume plus many baffles, or wipes. It is possible to design a very small and compact suppressor with wipes which effectively silences a pistol; these suppressors have a lifetime of as few as 4-5 shots and typically no more than a few magazines of ammunition. Larger wipeless (baffle only) pistol or rifle suppressors may be nearly as effective for long lifetimes (hundreds or thousands of shots) but are relatively bulky, clumsy, and heavy.

Most suppressors designs trade reduced total volume and weight for somewhat louder noise, which is still significantly tactically useful. The optimum point for any particular design depends on the suppressor's intended usage.

Wet suppressors
Some suppressors, called "wet" suppressors or "wet cans", use a small quantity of water, oil, or grease in the first chamber to cool the powder gasses and reduce the volume (See ideal gas law). The coolant lasts only a few shots before it must be replenished, but while it lasts it can greatly increase the effectiveness of the suppressor. One manufacturer claims a 30% improvement in sound suppression for "4 magazines" (32 to 68 rounds) with the addition of 5 ml of water or light oil to their suppressor. Water is most effective, due it its high heat of vaporization, but it can leak or evaporate out of the suppressor. Grease, while messier and less effective than water, can be left in the suppressor indefinitely without losing effectiveness. Oil is the least effective (and least preferable, as well), as it leaks while being as messy as grease, leaving behind a fine mist of condensed oil after each shot.

It is widely believed that suppressors can be improvised with any baffling material. Such attempts are only marginally useful, have a very short lifespan even if effective, and are often dangerous to the user. In areas where suppressors are regulated, such improvised suppressors are usually illegal regardless of whether they actually reduce the sound of a firearm. Even suppressors intended for paintball guns, while providing no functionality for firearms, are illegal in the United States. Nonfunctioning/dummy silencers are available for replica enthusiasts and are generally legal in most states in the United States.

The overwhelming majority of improvised suppressors popularized by movies and television (plastic bottles, potatoes, pillows, etc) do nothing to dampen a gunblast.