Did you ever see that movie Shooter with Mark Wahlberg?  In one scene he creates a makeshift suppressor on the end of a rifle with a water bottle.  He then fires the suppressed rifle whilst riding in a moving boat accurately engaging targets.  That being said, many have questioned the validity of accurately shooting from a moving boat the water bottle silencer.

The Sportsman's Guide offers a unique product called The Tipton Patch Catcher which attaches a bottle to the end of a barrel to aid in rifle cleaning.  Cough, cough, wink, wink.  I have to sediments about this product.  First, does anyone really have problems with patches falling on the ground?  Buy a damn bore snake and you'll have no problems.  Second, I see visions of redneck injuries by not properly conducting makeshift rifle silencers. Not to mention a homemade silencer/suppressor is a felony.

So you're still wondering, despite Mark Wahlberg and red necks, do the bottle silencers work?  Yes, sort of... As you can see in the above video, a felony is being committed a water bottle does work.  What the water bottle is doing is slowing the bullet down; to achieve even more "silence" subsonic bullets are needed.   

Don't be stupid kids, felonies are bad.  If you get caught with a DIY suppressor you'll be in deep crap.