In firearms, a choke is a tapered constriction of the gun barrel's bore at the muzzle end, almost always used with shotguns. The purpose is to decrease the spread of the shot in order to gain better range and accuracy.[1]
The exit end of the choke is smaller by some dimension than the actual bore of the barrel. This difference is the amount of constriction. Generally the ranges for chokes will be 0.00-1.15 mm (0.00-0.045 inch), while the constriction for turkey chokes may be as much as 2.50 mm (0.10 inch). Choke is measured by the percentage of pellets in the charge that will impact inside a 30" circle at 40 yards (25 yards for "cylinder" and "Skeet1").[2] Although different choke manufactures have different identification of their chokes, the notches in the chart below are generally accepted.[3]
| Choke | Constriction | Percent | Identification (Notches) |
|---|---|---|---|
| Cylinder | .000 | 40 at 40 yd 70 at 25 yd |
IIIII notches |
| Skeet 1 | .005 | 45 at 40 yd 75 at 25 yd |
|
| Improved Cylinder | .010 | 50 | IIII notches |
| Skeet 2 (light Mod.) | .015 | 55 | |
| Modified | .020 | 60 | III notches |
| Improved Modified | .025 | 65 | II notches |
| Full | .030 | 70 | I notch |
| Extra Full | .040 | 73 | |
| Turkey | .045 plus | 75 plus |
In turkey shoots, a competitor may use his own shotgun (typically 12 gauge) however he likes, and most competitors employ turkey chokes in order to maximize the amount of shot striking the target. Some turkey shoots do not allow chokes for this reason.
A choke is designed to alter the distribution of the shot as it leaves the firearm. For shooting most game birds and clay pigeons, a desirable pattern is one that is as large as possible while being dense enough to ensure multiple hits on the target. Shotguns intended for defensive use often have cylinder or improved cylinder chokes for the widest shot pattern at typically short defensive range.