The "choke" of a shotgun is a small constriction applied near the muzzle of the barrel that effectively changes the patterning characteristics of the shot as it passes through. The constriction is the difference between the tightest inside diameter measurement of the area of choke, and the actual bore diameter. For example a typical 12 gauge barrel has an inside diameter of .729" the chokes for this bore size would run from cylinder at .729" to Full at .689".
| Points** | Inches | American | European | % of Pattern in 30" circle @ 40 yards*** |
|---|---|---|---|---|
| 0 | .000 | Cylinder | S | 40% |
| 5 | .005 | Skeet | VZ | 45% |
| 10 | .010 | Improved Cylinder | 1/4 | 50% |
| 15 | .015 | Skeet #2 | - | 55% |
| 20 | .020 | Modified | 1/2 | 60% |
| 30 | .030 | Improved Modified | 3/4 | 65% |
| 35 | .035 | Full | 1/1 | 70% |
| 40 | .040 | Extra-Full | - | 75% |
|
* Shotgun chokes specifications can vary greatly from manufacturer to manufacturer. The above table is representative of typical values only. The only way to accurately determine your guns choke and patterning characteristics are to measure the bore choke relationship, and pattern you gun with the desired
shot-size/load. **Points are the actual physical measurement of choke in .001's (thousandths of an inch) ***The 12ga, 16ga, and 20ga. are all patterned at 40 yards for choke evaluation. Both the 28ga, and the .410 are typically patterned at 30 yards. You can expect similar percentages at this shorter range. | ||||
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