Knowing the diameter of a choke tube is important in order to identify choke tube constriction. The tighter the choke tube, the more constriction and the less constriction, the more open a choke will be.
Choke sizes are classified by both their measurement (to a thousandth of an inch) and by a special naming system. Choke measurements range from open chokes of around 0.735 to 0.770, to more restrictive chokes of around 0.600 to .0680. Choke tubes are also classified by a naming structure that includes (from open to tight) cylinder, skeet, improved skeet, improved cylinder, light modified, modified, improved modified, light full, full, extra full, and turkey.
Choke Tube Constriction Chart
The choke tube table above shows the diameters and constrictions you can expect for choke tubes and shotgun barrels of a specific make and type, as well as for 12-gauge, 10-gauge, 20-gauge, 16-gauge, 28-gauge, and .410 shotguns. Most popular choke systems are shown which include, Browning Invector, Invector Plus, Remington, Winchester Invector, Benelli, and Beretta.
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Choke Tube Markings
Markings on choke tubes come in a wide range of variations, but their meaning across the spectrum is largely the same. Manufacturers can use a notching/serration system, color coded, alpha naming scheme, and color banding to indicate the diameter of the choke tube. This is done for quick verification without having to remove the choke from the gun in most cases.
Browning Choke Tube Markings
I – Full Lead or Steel
II – Modified Lead, Improved Modified Steel
III – Improved Cylinder Lead, Modified Steel
IIII – Skeet Lead, Light Modified Steel
None – Cylinder Lead, Improved Cylinder Steel
Benelli Choke Tube Markings
I – Full
II – Improved Modified
III – Modified
IIII – Improved Cylinder
V – Cylinder
Beretta Choke Tube Markings
I – Full
II – Improved Modified
III – Modified
IIII – Improved Cylinder
V – Cylinder
Choke tube diameter is measured from the inside walls of the choke and recorded to a thousandth of an inch. This measurement determines the choke tube size. Choke tube markings are an easy way to visually confirm choke tube diameter without having to measure.