Shotgun Choke Tubes

-- by Rob Ramsdale --

At one time, all shotguns had no choking on their barrels at all. Each shotgun had a barrel that was the same diameter all of the way down the barrel. Then several different people during the mid- 1800's discovered that if they constricted the barrel some near the muzzle, they could get improved, tighter patterns from their shotguns. There were several people world-wide working on this at the same time so it's hard to say who came up with the idea first . All we know now is that it works very well.

Choke Defined

Choke is a carefully measured constriction of the bore of a shotgun at the muzzle, designed to control the spread of the shot as it leaves the barrel.

Choke classifications are determined by measuring the barrel with a bore micrometer. The internal diameter is measured four inches from the muzzle and again just at the muzzle. Subtracting gives the amount of constriction in thousandths of an inch.

Below are descriptions of each shotgun gauge and their constrictions for each common choke designation. The pattern percentage is the percentage of the pellets from a shell shot through that choke restriction that hit inside a 30" circle at 40 yards distance.

Of course, the dimensions used in the above table are only rules of thumb. Bore measurements by micrometer are useful to predict the pattern thrown by a shotgun barrel, but they remain merely a prediction. The only way to determine the actual pattern thrown by a shotgun barrel is to shoot it at 40 yards, count the percentage of pellets falling within a 30" circle placed around the visual center of the pattern (as in the right-hand column of the above chart), then repeat it a few more times and take an average.

Modern turkey chokes definitely fall into the "xtra full" range on this chart. Some of these chokes when used with the right shell and gun will throw 95% patterns at 40 yards.