Ok I'm in the slow process of getting into hunting and have yet to take the required hunter-safety course.  Some cousins and friends of mine shoot but I've yet to get a clear picture of how shotgun chokes function.  Will someone please pretend that I know nothing about chokes and their use and break it all down for me.
 
-kevin

Well, Kevin, I hope I can help as it seems u haven't gotten a reply yet.  The chokes of a shotgun control the tightness of the shot pellets while shooting.  The most sparse pattern is given by a open cylinder (no choke), followed by improved, modified, full and extra full (usually for turkey and only lead shot).  As you start with the open cylinder, the pattern of your shot will "open up" more quickly when it leaves the barrel and thus, cut down the overall range of the gun.  When you use a full or extra full choke, the pattern will hold more tightly, making it more effective at a longer range.  Again, be sure if you get a extra full turkey choke that you use it with lead only.  Manufacturer rules, you know :-)  I hope this helps...

Roadkill pretty much covered it Kevin. Choke 'constriction' is measured in thousandths (i.e. .010") and sometimes refered to as 'points'.

The idea is to have a shot pattern, that has no holes, within a 30" circle for the type of birds you are hunting. Close hunting would be about 15 yards...longer ranges would be about 45 yards. You want enough pellets to kill the bird but you do not want to make mince meat out of it.

Upland game can still be hunted with lead pellets but Federal birds like ducks and geese, require hard shot like soft steel, bismuth, etc. This is important as the hard shot does not react the same as lead through the chokes and, usually, requires a slightly more 'open' choke.

Match the shotgun gauge, choke and pellet size to the game you are hunting (within existing game laws in your state). This can be a very interesting quest and is subject to much debate (and hot air) regarding gauge, choke, barrel length, type of shotgun, pellet size, velocity and hunting styles. Welcome to the world of opinion.

Below is shown different choke designs.

In very simple terms...think of it as a funnel.  The the shot is forced thru a more narrow opening makes a tighter pattern. This means the shot does not spread out very much (Full or "Turkey" choke) If its not funneled down at all it allows the shot (bb's) to spread apart more after leaving the barrel. (Improved Cylinder or Cylinder Choke) There are others in between but i hope this helps some.

Thanks for the info this is pretty much what I had pieced together and then some.  On a related note does barrel length affect the pattern at all?  Is the difference between a 24" and an 18" just the smoothness or quickness of getting a bead on a bird?
 
 -Kevin

You've got it Kevin.  This idea that a longer barrel shoots further is one of the 'old wives tales' that I've fought for many years.

Put a full choke on a 30" barrel.  Take that exact same choke and put it on a 48" barrel.  The fact is that the shot starts spreading after exiting the barrel at the same rate with each barrel.  So...does the longer barrel shoot further?

Yup!  18" further.  

What can happen is that the longer sight radius and heavier barrel can give you a smoother swing and make you a little more accurate at your maximum range.

I remember a friend taking me out to his expensive 'blind' when he finally got his new Savage O/U in 3".  I took along my Remington 870 in 20 gauge 2 3/4" with 28" barrel.  When we came back we had our birds on his fancy hand-tooled game strap.  All my birds on one side...all his bird on the other.

The barrel and chamber didn't make the difference but all things considered, he should have had an advantage with a little more shot in his pattern.  At the trap range, he and I shot about the same.  My personal opinion is that he thought the 3" with the longer barrels would make the difference and he counted on that rather than concentrating on swing and follow through.

Trying to remember the burn rate on powders for shotguns. If memory serves the powder is completely burned at around 16" of barrel on average. Longer barrels only improve sight radius, possibly follow through and can help balance in the gun. They will not shoot any further or harder than a short barrel. Despite all the "long tom" single shots from days gone by.