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.
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
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.