Choke Tube Primer


Dear Readers,

Some years ago I was at a “product testing” goose hunt. While
that sounds like the typical outdoor writer’s boondoggle, these things
really are a good way to take a quick look at the latest products. The
hunts lead to phone calls and personal contacts where the real
information comes.

The Charles Daly line of guns we were shooting on this goose hunt were
fitted with Trulock Chokes. Some time after the hunt, George Trulock
called up and asked how I liked his chokes. Well, that’s a tough
question. When I had pointed my gun right, the geese fell down. When I
had screwed up, they didn’t. Half a dozen dead geese over a few days
are hardly a litmus test of a choke. I confessed this to George and we
started talking about choke development and choke testing in general.
I learned a great deal from him about what we know about how chokes
work and what we don’t. One thing for sure is that choke design is not
cut and dried. People have been fussing with different choking methods
for 125 years and still can’t explain exactly how and why things work
the way they do. George sent me some chokes to play with, particularly
some tight ones, and I’m testing them between snow storms.

In the meantime, I thought it would be interesting to post the choke
information below from George and Jerrod Trulock. It’s a basic primer
in shotgun chokes and patterning, but it also contains a few pretty
advanced bits too. Reread the comments in bold type. They are
absolutely, positively true.

You might also visit the Trulock Choke site and take a look at his products.
The chokes he sent me (black anodized, extended, knurled) for use in
my Berettas were a perfect fit, not always the case with aftermarket
chokes. They were also very well machined with a uniform finish on the
interior. Trust me, that’s not the case with every brand of
aftermarket choke out there. I’ve seen a couple of brands of
aftermarket chokes with interior finishes varying from rough to smooth.

Trulock’s knurled extended part was clearly marked with the choke
designation name (Imp Cyl, Skeet 2, etc). I could read the markings
without my glasses. Nothing is more irritating than teeny weeny
invisible choke markings that require a microscope to decipher.
Equally importantly the body of the Trulock choke was marked with the
actual I.D. of the choke in thousandths of an inch. Trulock choke
designations come every .005″ on the five thou – .700″, .705″, .710″,
etc. If you take the time to measure your gun’s barrel bore ID (my
Beretta 303 and 391 autos are all right about at .722″) a bit of quick
subtraction gives you the exact amount of constriction. Example: .722″
bore ID minus the marked choke ID of .710″ equals a constriction of
.012″. As a Technoidal type, I like to know this. Of course, as George
points out below, this only tells you just so much. You must pattern
to really know what you have with your particular shell. His comments
that different shells pattern differently is really true. You won’t
believe how much difference there can be until you see for yourself.
Chokes are an important part of patterns, but they aren’t the only
part. You’ll never get a reliably good pattern with a lousy choke, but
you sure can get lousy patterns with lousy shells no matter which
choke you use.

Read the stuff below. I’ll bet you find something in there you didn’t
know. I sure did.

Best regards,

Bruce Buck
The Technoid writing for Shotgun Report, LLC
(Often in error. Never in doubt.)
<http://www.ShotgunReport.com&gt;

From George Trulock, Trulock Chokes.

Basic Choke Information

What Is A Shotgun Choke?

A choke is simply a tapered constriction of the gun barrelâs bore at
the muzzle end. The exit end of the choke is smaller by some dimension
than the actual bore of the barrel. This difference is the amount of
constriction. For example if the bore of the barrel is .730 and the
exit dia of the choke is .710 you have a constriction of .020. The
amount of constriction for a given degree of choke will also vary
between manufacturers but as a general rule for standard chokes the
total range will be between .000 and .045 thousandths of an inch. In
the case of special purpose turkey chokes it can be as much as .100
or 1/10th of an inch. The length of the choke can vary as well. Most,
but not all chokes will have an overall length of between 1.5 and 4
inches.

They can be grouped in 3 general types:

1- Fixed chokes- They are made as an integral part of the barrel
and cannot be readily changed except by a gunsmith and any alteration
is considered permanent.

2- Interchangeable chokes- These can be of the Îscrew onä style
which is externally attached or the ãscrew inä which is recessed into
the barrel. To change the degree of constriction you simply remove and
replace with a choke of a different diameter.

3- Adjustable chokes- This style of choke is adjustable throughout
the entire range by turning a sleeve, which collapses or allows a
collet to expand thus changing the exit diameter. A popular choke of
this type is the Polychoke.

The internal design of chokes can also be broken down into three main
groups:

1- Conical Parallel- They have a cone that blends into a parallel
section which helps to stabilize the shot charge as it leaves the
choke.

2- Straight Conical- This has a cone only. Where the cone stops is
the point where the shot exits the choke.

3- Wad Retarding-They do not have the constriction in the same
manner as either of the above designs but instead use bumps or
projections to alter the shot pattern.

The most common design in use is the conical parallel. All Trulock
Chokes are of this design.

Shotgun Patterns

Patterns are normally expressed as a percentage such as 50%, 60%, 70%
ect. This is the commonly accepted method comparing pattern density.
In a 50% pattern¸ of all the pellets contained in the shell will
strike inside of a circle of 30 inches in diameter. To find the
percentage of any given load divide the number of hits inside the
circle by the total number of pellets contained in the shell. You can
obtain the approximate number of pellets any given load will have from
a shotgun shell reloading book or you can open a couple of shells and
actually count the pellets. All pattern testing is done at a distance
of 40 yards with the exception of cylinder and skeet 1 chokes in all
gauges and all chokes for the .410 bore which are normally measured at
25 yards.

The purpose for this is to allow you to select a choke that will throw
a pattern that is as large as possible without having the pellets so
far apart that the target can escape multiple hits. For shooting both
game and clay targets you want a pattern that is perfectly even in
pellet distribution over the 30-inch circle. Having said that, and
after looking at thousands of patterns over a span of 25 years I could
count on my fingers the number that I would call perfect and if these
were measured close enough they would not have qualified. In this
instance very close is good enough. Two exceptions to the preceding
would be buckshot and turkey patterns. With both of these you are
looking for a tight center cluster of pellets.

One thing to remember. The only thing that is consistent about
shotguns is that very few things are consistent. Identical guns with
the same degree of choke and using the same shell may not pattern the
same. The same load between various brands of shells can pattern
differently. Patterns will change when changing from hard to soft
shot. Patterns can change when anything in the shell changes such as
different wads, powders or primers. What I am trying to get across is
that when you change anything such as brands, shot size, or components
you will need to check the pattern as it could have changed, sometimes
by an extreme amount.

Once you find a choke/shell combination that gives you the pattern you
want it should remain reasonably consistent as long as nothing is
changed. I am satisfied as long as the percentage stays within a 5%
plus or minus deviation.

The chart at right shows the relationship between the degree of choke,
the percentage and constriction based on lead shot. Keep in mind that
the percentages are a guide only. What you actually want is a pattern
that is dense enough to insure multiple hits on your target at the
distance you normally shoot.

 

 

 

 

 

 

 

Keep in mind that this chart should be used as a starting point only.
Select the choke and pattern it. Change chokes or loads as needed to
get the pattern you want. If you do not pattern your gun please feel
free to accept this chart as being infallible.

How To Pattern

I like to use paper that measures 4 feet square. Paper this size may
be hard to find locally.

If it is not available try taping several sheets of butcher paper
together. The reason for the large paper is that if your gun does not
shoot to the point of aim part of your pattern could be off of the
target with a small paper and you could confuse this with a bad
pattern. If it helps you, mark the target center for use as an aiming
point. I prefer to use a rest when shooting. If you do make sure the
gun is not touching any hard object. The reason for using a rest is
that it helps remove some of the variables. From the correct distance
shoot at the center of the target. I would do this a minimum of 5
times on different targets with each shell or choke that is being
tested. You will need to draw a 30-inch circle around the most dense
portion of the pattern on each target. Count the pellets inside of the
circle. Divide this number by the total number of shot contained in
the shell and you will have your percentage. Average your percentage
by the total number of shots fired with the particular shell or choke
to obtain your overall average. Sounds like a royal pain doesn’t it?
It is, but there are no short cuts if you really want to know what
your shotgun is doing.

After you have finished look carefully at each pattern for holes that
are big enough to let your intended target slip through. You want a
dense enough pattern to ensure multiple hits.

Steel Shot/Waterfowl Chokes

Much has changed over the years with steel loadings. The quality and
consistency of the shells has been greatly improved. However the fact
that steel shot is exerts much more stress on choke tubes has not. The
problem is that steel shot is much harder than lead. It will transmit
much more energy to the choke when it strikes the conical portion and
if the tube is not of sufficient strength it will cause it to deform.
This is known as choke creep.

Over a period of time choke creep can lock a choke in the barrel so
that it is next to impossible to remove. All Trulock Chokes are rated
for use with steel shot from cylinder bore through improved modified
with the exception of the Tru-Choke S.D. which are not recommended for
any shot other than lead. In addition our Super Waterfowl Choke was
designed especially for steel and all other environmentally friendly
shot.

It is strongly suggested that you use our Extended Precision Hunter
style choke for steel shot as they normally give a superior pattern
over the flush style chokes.

Close Range öapproximately out to 30 yards – Skt 1= pattern
percentage of about 55% Medium range- approximately out to 35
yards-Skt 2 [light mod] =pattern percentage of 65%

Long Range-35yards and further- Improved Modified =pattern percentage
of 75%

Extreme Range= Super Waterfowl series

These suggestions should be used as a starting point and should not be
taken as a substitute for patterning your shotgun.

Alternative Alloy Shot These are recommendations for Trulock Chokes
only

Tungsten Iron- Treat this shot the same as steel

Tungsten Polymer- Treat this shot the same as lead

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