Open Choke or Tight Choke? 

Posted On: 04-20-2024

I did a little reading about chokes and choke tubes and I feel they are worth sharing.  Andy Kirkland provides a download through the Institute of Clay Shooting Instructors so credit him on my newfound wisdom.  The hyperlink above is a download link so the document will be available to you as well.

In the simplest terms a standard exists for the bore of a shotgun.  I will continue with that simplicity by only explaining a 12 gauge.  The bore standard for a 12-gauge shotgun is .729 inches.  This is established by the Sporting Arms and Ammunition Manufacturers Institute.  History tells us the way a gauge was determined formerly was by using lead balls of equal size and adding them to the barrel.  If the barrel held 12 balls it was determined a 12-gauge bore. 

When we start with a .729” bore our chokes are designed to restrict that bore and as we know a 12-gauge full choke is tighter than an open cylinder bore choke.  So simply adding a full choke tube and restricting by .035 inches our final bore is .694 inches.  Typically chokes have these restrictions:

Cylinder Bore = .000 > .729

Skeet I = .005> .724

Improved Cylinder = .009> .720

Skeet II = .012 > .717

Modified = .019 > .710

Improved Modified = .025 >.704

Full Choke = .035 > .694

Extra Full = .040 > .689

While the choke restricts the bore there are also other things that impact how the shot performs once it leaves the barrel.  Pressure behind the wad, hardness of the shot and altitude can change the patterns and shot string.  So, the one thing I learned in reading this article was how one might think a full choke would have the longest shot string.  Consider these strings at nearly 10 – 12 feet at 40 yards.  I have written about shot strings in that a dusted target is one that has the target passing into the tip of the string and then the entire shot string passes through the target completely puffing the target. 

Back to how one thinks a shot string is longer with a tight choke.  Reality is just the opposite because of the pressure required to push the wad and shot out of the barrel the shot is compressed and therefore not able to spread out.  In an open choke less pressure behind the wad allows the shot to extend and spread more.  I am not advocating for an open choke in trap but understand how the shot string works under the pressure of a full choke.  The full choke produces a more dense, shorter and slower spreading pattern. 

To put all this into perspective consider when changing loads or shot size as to how this can impact you shot string performance.  As is always the case a trip to the pattern board is required with any of the above loads or choke tube changes.  Remember these parameters;

Full pellets in 30” circle = 70%

Improved Modified = 65%

Modified = 60%

Improved Cylinder = 55%

Skeet = 50%

Cylinder = 40%

David R.Vaught, Ph.D.

Executive Directorr