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Understanding Shotgun Chokes

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PostPosted: Tue Sep 13, 2011 12:29 am
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Shotgun chokes were designed to control pattern diameters at different yards. What is a pattern? It is just the grouping of the pellets at a given yardage. This grouping or pattern is measured by a circle diameter. This particular circle must have certain efficiency. In other words, it has to have a certain number of pellets in a given area (called distribution) for it to be labeled an efficient pattern.

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Here is a quick reference chart:

Shotgun Choke..... Yardage...........Shotgun Choke Restriction

Cylinder................... < 20.......................... 0
Skeet...........................22.5......................... .005 (of an inch)
Improved Cylinder....... 25............................... .010
Light Modified...............30................................... .015
Modified....................... 32.5.................................... .020
Improved Modified........ 35.......................................... .025
Light Full....................... 37.5........................................... .030
Full............................... 40+................................................. .035
Extra Full...................... 40+.................................................... .045
Super Full......................40+........................................................ .055

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How does a shotgun choke actually work ?

There are two forces that tell the story... the mechanical properties while the shot column is in the barrel and the dynamic forces of nature that affect the shot column after it exits the barrel. When the shot column meets up with the choke it forces the column to squeeze tighter together; these forces are called radial forces. Once it is out of the barrel, wind resistance and gravity act on it. When the wind comes into contact with the outside pellets of the shot column it induces spinning and they start to flare off like a ping pong ball with english on it.

The tighter the choke the heavier the radial forces, the tighter the pellets are squeezed together so the pattern holds tighter over a longer distance.

Conversely, the less restriction you have in the choke the more loosely the pellets are held together and the faster the pattern opens up.

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PostPosted: Tue Sep 13, 2011 1:33 pm
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Chokes may either be formed as part of the barrel at the time of manufacture, by squeezing the end of the bore down over a mandrel, or by threading the barrel and screwing in an interchangeable choke tube. The choke typically consists of a conical section that smoothly tapers from the bore diameter down to the choke diameter, followed by a cylindrical section of the choke diameter. The use of interchangeable chokes has made it easy to tune the performance of a given combination of shotgun and shotshell to achieve the desired performance.

The choke should be tailored to the range and size of the targets. A skeet shooter, shooting at close targets might use a skeet choke (.005 inches of constriction) to produce a 30 inch diameter pattern at a distance of say 22.5 yards. A trap shooter...shooting at distant targets may use a light full choke (.030 inches of constriction) to produce a 30 inch diameter pattern at just under 40 yards.
Special chokes for turkey hunting...which requires long range shots at the small head and neck of the bird...a hunter may use a super full choke equaling roughly .060 inches of constriction. The use of too much choke and thus a small pattern increases the difficulty of hitting the target while the use of too little choke produces large patterns with insufficient pellet density to reliably break targets or kill game.

( Below for Oli... ;) )

Shotguns generally have longer barrels than modern rifles. Unlike rifles, however, the long shotgun barrel is not for ballistic purposes. Shotgun shells use small powder charges in large diameter bores, and this leads to very low muzzle pressures and very little velocity change with increasing barrel length. Since shotguns are generally used for shooting at small, fast moving targets, it is important to lead the target by firing slightly ahead of the target...so that when the shot reaches the range of the target, the target will have moved into the pattern. On uphill shooting, this means shooting above the target. Conversely...on downhill shooting, this means shooting below the target, which is somewhat counterintuitive for many beginning hunters. Of course, depending on the barrel length, the amount of lead employed will vary.

Shotguns made for close ranges, where the angular speed of the targets is great (such as skeet or upland bird hunting) tend to have shorter barrels, around 24 to 28 inches. Shotguns for longer range shooting, where angular speeds are less (trap shooting; quail, pheasant, and waterfowl hunting) tend to have longer barrels, 28 to 34 inches. The longer barrels have more inertia, and will therefore swing more slowly but more steadily. The short, low inertia barrels swing faster, but are less steady. These lengths are for pump or semi-auto shotguns as break open guns have shorter overall lengths for the same barrel length, and so will use longer barrels. The break open design saves between 3.5 and 6 inches in overall length, but in most cases pays for this by having two barrels...which adds weight at the muzzle. Barrels for shotguns have been getting longer as modern steels and production methods make the barrels stronger and lighter as a longer, lighter barrel gives the same inertia for less overall weight.

Shotguns for use against larger, slower targets generally have even shorter barrels. Small game shotguns, for hunting game like rabbits and squirrels, or shotguns for use with buckshot for deer, are often 22 to 24 inches in length.

Shotguns intended for all-round hunting are a compromise...but a 28 inch barrel pump action 12 gauge shotgun with a modified choke can serve as a general all around hunting gun for small game in semi-open wooded or farmland areas where dense brush is less of a hindrance and the ability to have more reach is important. For hunting in dense brush, shorter barrel lengths are often preferred.

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PostPosted: Tue Sep 13, 2011 1:35 pm
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As everyone here already knows, Shotgun shells are generally measured by "gauge"... though in other locations outside the United States the term "bore" is used with the same meaning. Where as rifles and handguns are almost always measured in "caliber"...which is simply a measurement of the internal diameter of the barrel measured in fractions of an inch and consequently is approximately equal to the diameter of the projectile that is fired. By contrast, shotguns are also measured by "gauge"...which is the weight (in fractions of a pound)...of a pure lead round ball that is the same diameter as the internal diameter of the barrel.

For example, a shotgun is called 12 gauge because a lead sphere that just fits the inside diameter of the barrel weighs 1⁄12 of a pound. This measurement comes from the time when early cannons were designated in a similar manner...a "12 pounder" would be a cannon that fired a 12 pound cannonball, thus inversely, an individual "12 gauge" shot would in fact be a 1⁄12 pounder. Thus, a 10-gauge shotgun has a larger-diameter barrel than a 12-gauge shotgun, which has a larger-diameter barrel than a 20-gauge shotgun, and so forth.

Shotshells are loaded with different sizes of shot depending on the target. For skeet shooting, a small shot such as a # 8 or #9 would be used, because range is short and a high density pattern is desirable. Trap shooting requires longer shots, and so a larger shot, up to #7½ would be desired. The smaller the shot (#9 for example)...the more receptive it will be to being constricted or "choked" than larger shot (say #4) due to space for displacement within the load.
( ^^^ Thanks... John A. ;) )

For hunting game, the range and the penetration needed to assure a clean kill must both be considered. Shot loses its velocity very quickly due to its low sectional density and ballistic coefficient. Small shot, like that used for skeet and trap, will have lost all appreciable energy by 100 yards or meters, which is why trap and skeet ranges can be located in relatively close proximity to inhabited areas with negligible risk of injury to those outside the range.

Birdshot sizes are numbered similar to the shotgun gauges; the smaller the number, the larger the shot. For hunting, shot size must be chosen not only for the range, but also for the game. The shot must reach the target with enough energy to penetrate to a depth sufficient to kill the game. Lead shot is still the best performer for the money, but environmental restrictions on the use of lead, especially with waterfowl, require steel, bismuth, or tungsten composites. Steel, being significantly less dense than lead, requires larger shot sizes, but is a good choice when cost is a consideration. Steel, however, cannot safely be used in some older shotguns without causing damage to either the bore or to the choke of the shotgun due to the hardness of steel shot. Since tungsten is a very hard metal, it must also be used with care in older guns. Tungsten shot is often alloyed with nickel and iron, softening the base metal. That alloy is approximately 1/3 denser than lead, but far more expensive. Bismuth shot falls in between steel and tungsten shot in both density and cost.

Larger sizes of shot, large enough that they must be carefully packed into the shell rather than simply dumped or poured in, are called "buckshot" or just "buck". Buckshot is used for hunting larger game, such as deer (hence derivation of the name), and also in riot shotguns and combat shotguns for defensive, police, and military use. Buckshot size is designated by number, with smaller numbers being larger shot; sizes larger than "0" ("ought") are designated by multiple zeros. "00" ("double ought") and "000" ("triple ought") are the most commonly used sizes.

A standard 00 buck shell holds 7-9 pellets. Two types of 00 buckshot are commonly available...regular 00 buckshot shells, and reduced-recoil shells favored in law enforcement or home defense use. Low-recoil 00 buckshot allows the shooter to make fast follow-up shots, which may be needed in a combat situation, but are not typically required in hunting where the main goal is to cleanly take out the game with a single shot.

For narrower patterns...a buffering material, such as granulated plastic or similar material can be mixed with the shot to fill the spaces between the individual pellets. When fired, the buffering material compresses and supports the shot, reducing the deformation the shot pellets experience under the extreme acceleration. Copper plated lead shot, steel, bismuth, and tungsten composite shot all have a hardness greater than that of plain lead shot, and will deform less as well. Reducing the deformation will result in tighter patterns, as the spherical pellets tend to fly straighter. One improvised method for achieving the same effect involves pouring molten wax into the mass of shot...which will keep it together longer, but tends to foul the barrel quicker.

Shooting lead shot will result in more shot deformation and a wider pattern...as the lead used will have minimal alloying elements and be very soft. Spreader wads are wads that have a small plastic or paper insert in the middle of the shot cup, usually a cylinder or "X" cross-section. When the shot exits the barrel, the insert helps to push the shot out from the center, opening up the pattern...but often result in inconsistent performance. Intentionally deformed shot...ellipsoidal shape or even cubical shot will also result in a wider pattern, much wider than spherical shot, with more consistency than spreader wads. Hunting loads that use either spreaders or non-spherical shot are usually called "brush loads", and are favored for hunting in areas where dense cover keeps shot distances very short.

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PostPosted: Tue Sep 13, 2011 1:50 pm
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The floor is open to thoughts, additions, diversions, detractions and other comments... 8-)

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PostPosted: Wed Sep 14, 2011 1:53 am
Some choke makers list their constrictions in micrometers...here's a list to break the down:

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Micrometers..................Inches..................American Name

0.................................... .000......................... Cylinder
127................................ .005......................... Skeet
254................................ .010......................... Improved Cylinder
381..................................015......................... Light Modified
508................................ .020......................... Modified
635................................ .025......................... Improved Modified
762................................ .030......................... Light Full
889................................ .035..........................Full
1143.............................. .045......................... Extra Full
1270.............................. .055......................... Super Full

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PostPosted: Sun Sep 18, 2011 10:12 pm
Great Thread! This will definitely help many members.
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PostPosted: Mon Sep 26, 2011 8:15 pm
This chart will give an idea of what choke to use at what yardage for sporting clays... with the caveat that ammo, intended target, angle of presentation ( front, back, side ) also weigh in on the equation...

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Red - Pattern too small | Yellow - small but usable | Green - Optimal Pattern ===========================================================

Choke Tube Selection:

Choke tube selection is a confusing issue amongst a lot of shotgunners but one that is easily explained.

The real reason you want the right choke is to be able to place at least 70% of the shot in a 30" circle at 40 yards... the minimum / maximum pattern kill zone... meaning the pattern will cleanly kill anything in this circular zone.

Selecting the correct choke tube is nothing more than moving that same exact pattern to different yardages. In other words... if you want to shoot at a target 20 yards away then select a choke tube that gives you 70% of the pattern in a 30" circle at 20 yards...same if shooting at a target that is 45 yards away, select a choke tube that will give you 70% of the pattern in a 30" circle at 45 yards.

Extra Full Choke: ...................delivers a 70% pattern at 45 Yards.
Full Choke: ............................delivers a 70% pattern at 40 yards.
Modified Choke: ....................delivers a 70% pattern at 35 yards.
Improved Cylinder Choke: ....delivers a 70% pattern at 30 yards.
Cylinder Choke: ....................delivers a 70% pattern at 25 Yards.

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PostPosted: Wed Sep 28, 2011 1:27 pm
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From a 1961 Winchester catalog...

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**Thanks to GUNNER_D of the Winchester Owners Forum for this scan**

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PostPosted: Wed Sep 28, 2011 1:31 pm
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1961 Winchester Catalog...
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**Thanks to GUNNER_D of the Winchester Owners Forum for this scan**

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PostPosted: Wed Sep 28, 2011 1:34 pm
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1961 Winchester Catalog...
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**Thanks to GUNNER_D of the Winchester Owners Forum for this scan**

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