By carefully mating quality target loads with effective even-patterning chokes, the studied shotgunner can deliver clays-busting shot clouds downrange with confidence.

The question I am most asked by shotgunning clients relates to the subject of chokes and cartridges. There seems to be a belief that there is a magic formula of the two that, when discovered, can propel the clays competitor into a higher class, help win a tournament, or overcome inadequacies in their fundamental shooting skills. In effect, they are looking for a magic pill that does not exist and can be compared to the Middle Ages alchemist's obsession with attempting to turn lead into gold. You can have the finest combination of choke and cartridge, but unless you place the shot string onn line and in front of the target, it will not help you one bit.

So, first, I would like you to answer the following questions:
Are your target breaks chips or breaks around the edges of clays, or are they balls of dust? If safe to do so, can you collect complete missed targets and see if there are any holes in them? Do you shoot different disciplines with the same gun? Do you miss more than you hit? Do you shoot a fixed-choke gun? If one or more of your answers where "yes," then a better understanding of choke and cartridge choice could definitely improve your scores.

Let's begin with a brief history of choke and how its introduction resulted in changes over the years in both barrel and cartridge design. Before the invention of choke, all barrels where simply straight tubes (hence the expression "true cylinder") with an effective killing range of under 30 yards, with 25 being the norm. Anything hit beyond these ranges was a matter of luck.

The contested invention of shotgun choke between W. R. Pape, an Englishman, in 1866, and American Fred Kimble in 1870 was followed by W.W. Greener's research and development. Regardless, this key element of ballistics did more to increase the effective range of the shotgun than any invention since. It effectively changed the shotgun from a range of 30 yards to one of 50 yards. Since choke's major impact on range and effectiveness was recognized, it has been experimented with for the last 150 years to squeeze from it every last advantage of terminal ballistics.

What IS Choke?

To choke shot pellets means to constrict them with a tightening effect. The walls of the shotgun barrel are parallel, with the inside diameter at the muzzles becoming smaller. The amount of constriction is measured in thousands of an inch as compared to the nominal boring of the barrel. Ranging from the least degree of constriction to the greatest, there is a handful of major designations, these often measured in 10th inch increments and begin at true cylinder, where the barrels have no choke present. 

Terminology And Sizes

Different countries have differing terminology for the amount of choke present in a barrel, and that's where much of the confusion with chokes arises. Designated names and measurements in inches are used, and often with not much consistency. Generally, though, true cylinder offers no constriction, improved cylinder (or quarter choke) is .010", modified (half choke) .020", improved modified (three-quarter choke) .030", and full .040" choke. There are even choke constrictions designed for specific disciplines, such as "skeet" choke. 

Each manufacturer seems to have its own personal interpretation of what this amount should be, anywhere from .005" to .008" constriction. Add to the fray "spreader" or "diffusion" chokes, plus how back-bored or over-bored barrels affect choke dimensions/ designations, and the need for careful inspection and the use of a patterning board becomes evident--at least to the shotgunner who wants to know for sure how his loads pattern from his shotgun through a given choke.
 

Range And Distance

The function of choke is to increase the effective range of the shotgun. It achieves this by holding the shot charge closer together by reducing the amount of spreading once the pellets leave the barrel. Again, as a general guide, the optimum range of the various chokes is as follows:
Full choke: 30" pattern at 40 yards
Improved modified: 30" pattern at 35 yards Modified: 30" pattern at 30 yards
Improved cylinder: 30" pattern at 25 yards Cylinder or skeet: 30" pattern at 20 yards
A cylinder choke would be of little use at 40 yards, and vice versa, full is too tight at 20.

Fixed And Screw-In Chokes

Over the years, manufacturers have tried many choke designs. Conical, swaged conical, recess, cylindrical-conical, bell, trumpet, retro, parallel, and Tula are but a few. During the 1960s and '70s, it was a common practice of the sporting clays competition shooter to carry two guns, one a trap model with a good degree of choke plus and skeet model with its more open choking. This let the shotgunner choose the gun that was best choked for the target being shot. 

About that time, the refinement of the screw-in choke, revolutionized the clay target gun, creating a system where any shotgun could have its barrel machined and threaded to accept screw-in choke tubes of various constrictions. The choke--and therefore the width of the pattern--could be adjusted target to target. This process is now so popular, not only are many guns equipped as such from the factory, many specialist companies offer retrofitting of fixed-choked guns as well as custom-design replacement choke tubes for factory threaded barrels. Though we consider the screw-in choke a modern invention, it was invented by another English Victorian, Roper, who threaded the muzzle end of barrels to accept tubes of different constrictions.

Choke only works because of its difference in diameter to the nominal boring of the barrel. This interaction creates a problem, however, in that as the shot column is propelled down the barrel, it suddenly runs into a restriction to its passage, resulting in some of the pellets becoming crushed and deformed. As the deformed pellets exit the muzzle, they are slowed and deflected off path by the effects of air resistance. It was quickly learned that the more gradual the taper in the choke constriction, the less pellets are deformed. Specialist choke suppliers have refined their products to minimize the deformation of shot, and all modern chokes now are both longer and more parallel than the Victorian invention

The clay target shotguns of today fall into three categories. In trap and skeet, the distance and angle of targets thrown are fixed. This permits the choking of guns for these disciplines to be regulated accurately, maximizing the pattern width and density at set distances. Although many are, there is no requirement for trap and skeet guns to be multi-choked.

Sporting clays does not have set angles or distances, and with the variety of target sizes, course setters have become extremely ingenious in their presentations. It is the variety in these targets that makes sporting such an interesting and popular discipline along with requiring a shotgun that is far more flexibly choked, hence the popularity of screw-in chokes on sporting clays courses. 

The only way to determine precisely how your load/choke combo performs in your shotgun is a patterning session. At Nemacolin Woodlands' The Shooting Academy, a grease-covered metal plate with a hole in the middle to serve as an aiming point makes quick patterning checks a snap. For more difinitive evaluations, however, calculating pattern percentages from paper targets is still best.

Choke and its effectiveness are very much affected by your choice of cartridge. In fact, when choke was first used in shotguns, it actually resulted in worse patterns. Lead is a very soft metal quite prone to deformity. As the shot travels down the barrel at great speed and high pressure, it is inevitable that there will be some damage to its round shape. The degree of this damage relates directly to pattern quality. The more deformity, the poorer the pattern.

Much of this shot damage was prevented by the introduction of antimony into lead shot to increase its hardness. In addition to shot hardness, other components of the shotshell also affect its patterning performance.

The modern shotshell cartridge is, in effect, like the plunger or piston in a bicycle pump. The primer being struck ignites the powder that, combined with the case and crimp, creates sufficient pressure to propel the shot charge along and out the barrel. The wad must be capable of protecting the shot charge from the heat of powder combustion as well as barrel contact while at the same time acting as a piston and seal to make best use of the pressure generated. The shot must be of sufficient hardness to resist deforming while being driven down the barrel.

Wads are either felt, fiber, or plastic, the first two often being chosen for environmental reasons. There can be no argument that the plastic wad is superior, its shot cup protecting the pellets on their journey down the barrel.

Shot Size

The main shot sizes used for clays include No. 9s, 8s, and 7 1/2s. The larger the number the smaller the diameter of individual pellets--and the less energy per pellet. If you shoot 7/25, you have bigger shot and more striking power but fewer pellets than in an equivalent load of 8s. A simple rule of thumb is, out to 35 yards, stick to 8s; past that, 7 1/2s are best. Some shooters favor smaller 9s for wider, more dense patterns at really close targets.

Recoil

In recent articles, we have mentioned recoil, and the shotshell, aside from the weight of the gun, is a big factor in recoil control. You should take this into consideration when making your personal choice of shell. Excessive recoil is both fatigue inducing and the cause of many second-barrel misses.

Speed And Lead

The difference in lead required for a 40-yard target between the average and the fastest cartridge is but a few inches. Surely it is better to find a favorite cartridge and stick with it than continually experimenting with the rocket science of velocity's small effect on lead.

Chris Batha is the senior instructor and gun fitter for London Gunmakers E.J. Churchill. He has over 30 years experience in competitive clays shooting and wingshooting worldwide, has an international reputation as a shooting instructor, and has written extensively on all aspects of shotguns and their use. Batha is a former director of the British Clay Pigeon Shooting Association, with formal qualifications from a variety of other bodies, including the British Association of Shooting and Conservation, British City and Guilds, and National Association of Sports Coaches. He offers shooting instruction, gun fitting, and course design throughout the US.