Write an article based on this "You must calculate how much air expands in your gun's firing chamber. If you want to get some steel wool and line the inside of the pipe or bottle with it, the steel wool will absorb the sound a little better."
The silencer you build must have enough internal area to contain this volume of air.  In broad terms you must construct a can that mounts to the end of the gun that is closed on both ends. Inside the can there are several baffles. Through both ends and each baffle there must be a hole opened that allows the projectile to pass through. The hole should be a little bigger than the projectile to allow the projectile to pass through the ends and the baffles without touching the sides of the holes. The holes must also be exactly in a straight line, otherwise the projectile may strike the sides of one or more of the holes which will affect its trajectory.    {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/b\/bf\/Make-a-BB-Gun-Silencer-Step-4Bullet1.jpg\/v4-460px-Make-a-BB-Gun-Silencer-Step-4Bullet1.jpg","bigUrl":"\/images\/thumb\/b\/bf\/Make-a-BB-Gun-Silencer-Step-4Bullet1.jpg\/aid70081-v4-728px-Make-a-BB-Gun-Silencer-Step-4Bullet1.jpg","smallWidth":460,"smallHeight":345,"bigWidth":"728","bigHeight":"546","licensing":"<div class=\"mw-parser-output\"><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"https:\/\/creativecommons.org\/licenses\/by-nc-sa\/3.0\/\">Creative Commons<\/a><br>\n<\/p><p><br \/>\n<\/p><\/div>"}  Get a BB gun, preferably a rifle-like one. (It is possible to try this with a BB pistol, but it's a lot more difficult.)    {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/9\/9c\/Make-a-BB-Gun-Silencer-Step-4Bullet2.jpg\/v4-460px-Make-a-BB-Gun-Silencer-Step-4Bullet2.jpg","bigUrl":"\/images\/thumb\/9\/9c\/Make-a-BB-Gun-Silencer-Step-4Bullet2.jpg\/aid70081-v4-728px-Make-a-BB-Gun-Silencer-Step-4Bullet2.jpg","smallWidth":460,"smallHeight":345,"bigWidth":"728","bigHeight":"546","licensing":"<div class=\"mw-parser-output\"><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"https:\/\/creativecommons.org\/licenses\/by-nc-sa\/3.0\/\">Creative Commons<\/a><br>\n<\/p><p><br \/>\n<\/p><\/div>"}  Get a long (1 to 2 feet) pipe with a large enough diameter to fit over the front sights.    {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/d\/d7\/Make-a-BB-Gun-Silencer-Step-4Bullet3.jpg\/v4-460px-Make-a-BB-Gun-Silencer-Step-4Bullet3.jpg","bigUrl":"\/images\/thumb\/d\/d7\/Make-a-BB-Gun-Silencer-Step-4Bullet3.jpg\/aid70081-v4-728px-Make-a-BB-Gun-Silencer-Step-4Bullet3.jpg","smallWidth":460,"smallHeight":345,"bigWidth":"728","bigHeight":"546","licensing":"<div class=\"mw-parser-output\"><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"https:\/\/creativecommons.org\/licenses\/by-nc-sa\/3.0\/\">Creative Commons<\/a><br>\n<\/p><p><br \/>\n<\/p><\/div>"}  Fit the pipe over the front sights, so that is not at an angle that would prevent the BB from exiting the gun as it should. Optional: Use tape to secure the pipe.    {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/e\/e6\/Make-a-BB-Gun-Silencer-Step-4Bullet4.jpg\/v4-460px-Make-a-BB-Gun-Silencer-Step-4Bullet4.jpg","bigUrl":"\/images\/thumb\/e\/e6\/Make-a-BB-Gun-Silencer-Step-4Bullet4.jpg\/aid70081-v4-728px-Make-a-BB-Gun-Silencer-Step-4Bullet4.jpg","smallWidth":460,"smallHeight":345,"bigWidth":"728","bigHeight":"546","licensing":"<div class=\"mw-parser-output\"><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"https:\/\/creativecommons.org\/licenses\/by-nc-sa\/3.0\/\">Creative Commons<\/a><br>\n<\/p><p><br \/>\n<\/p><\/div>"}  Load and fire the BB gun. You should hear a low-pitched "thump" instead of the usual "pop".    {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/4\/41\/Make-a-BB-Gun-Silencer-Step-4Bullet5.jpg\/v4-460px-Make-a-BB-Gun-Silencer-Step-4Bullet5.jpg","bigUrl":"\/images\/thumb\/4\/41\/Make-a-BB-Gun-Silencer-Step-4Bullet5.jpg\/aid70081-v4-728px-Make-a-BB-Gun-Silencer-Step-4Bullet5.jpg","smallWidth":460,"smallHeight":345,"bigWidth":"728","bigHeight":"546","licensing":"<div class=\"mw-parser-output\"><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"https:\/\/creativecommons.org\/licenses\/by-nc-sa\/3.0\/\">Creative Commons<\/a><br>\n<\/p><p><br \/>\n<\/p><\/div>"}  Try different types and lengths of pipe.    {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/2\/28\/Make-a-BB-Gun-Silencer-Step-4Bullet6.jpg\/v4-460px-Make-a-BB-Gun-Silencer-Step-4Bullet6.jpg","bigUrl":"\/images\/thumb\/2\/28\/Make-a-BB-Gun-Silencer-Step-4Bullet6.jpg\/aid70081-v4-728px-Make-a-BB-Gun-Silencer-Step-4Bullet6.jpg","smallWidth":460,"smallHeight":345,"bigWidth":"728","bigHeight":"546","licensing":"<div class=\"mw-parser-output\"><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"https:\/\/creativecommons.org\/licenses\/by-nc-sa\/3.0\/\">Creative Commons<\/a><br>\n<\/p><p><br \/>\n<\/p><\/div>"} Your BBs might hit it though if the suppressor isn't on straight.