Theories, Myths, and Fables of Accuracy
A Key to Improved 22 Long Rifle Accuracy Discovered
This story starts over a decade ago, when I read
that measuring the rim thickness of 22 long rifle bullets would improve
accuracy. I also learned at this time
that some of the bench rest shooters were experimenting with weighing their
bullets to improve accuracy. Being of
solid Norwegian and German descent, you can’t tell me anything. Furthermore, even if you have proof, I will
still go out and prove it to myself. So
starts the last ten years of research that has finally yielded the first key to
improved accuracy for 22-caliber long rifle ammunition. This theory, applied from center-fire
experience, reduced group diameters by 35 percent (0.200 inches) with a target
grade test rifle at 50 meters.
Not only did I decide to sort ammunition by rim
thickness for accuracy testing, I also measured the rim concentricity, bullet
weight, bullet diameter, case diameter, length to ogive, velocity, and bullet
concentricity. In the tables of data
that I collected, the more expensive ammunition has a much smaller range of
variance for these measured aspects when compared to less expensive ammunition.
My initial testing was from hard sandbag rests
at an indoor facility with a 1413 Anschutz equipped with a 20x Unertl
scope. I originally shot 5 round
groups, and the testing grew to include seventeen brands of ammunition. The first tests that I conducted were for
rim thickness, bullet weight, and bullet concentricity. I already had a nice powder scale to weigh
bullets, and there were at least three different models of rim thickness
measuring tools on the market. However,
no one was offering a reliable tool to measure the bullet concentricity of 22
long rifle bullets. Therefore, I had to
build my own 22-caliber bullet concentricity gauge with my Unimat DB200
lathe/milling machine.
VIEW ORIGINAL CONCENTRICITY GAUGE
The data from the 1994 tests for rim thickness
and shell weight sorting was inconclusive.
The last test conducted at this range was for bullet concentricity. Bullet concentricity, also called run-out,
is the relationship of the bullet axis to the case axis as illustrated in
Figure 1. Finally, a test that actually
had some consistency in the data. The
data was not perfect because of my errors in technique. However, I had enough to convince myself to
continue testing.
Figure 1;
Part of my inconsistent results from the first
tests, Bullet Concentricity
were
due to my beginning incompetence of how
to
conduct
a shooting test and then how to interpret the
test
results. A decade later, now I believe
that some
of these other factors can and do influence
accuracy.
However, the results are small and masked in the bullet axis
data
by other dispersion factors (errors) that have
a greater influence on measured accuracy. For
those of us who don’t have access to the six
degrees
of freedom trajectory code, it may be important
to case axis
identify
the priority of accuracy influencing
errors.
We then can reduce or eliminate those errors that
have
a large influence on dispersion, and therefore
conduct tests with diminished masking errors.
My conclusion from the 1994 results was simple, I needed better facilities to conduct tests and collect data. Then a good friend of mine, Dr. Dan Durben, came through with a gift from heaven, permission to use the Olympic Training Center’s indoor shooting range. The Center’s indoor range is a 50 meter facility with electric target changers, and most importantly to me, a bench rail test vise. The bench rail vise at the OTC is the style that mounts a rifle in the stock and my 1413 Anschutz was again used for testing.
Once again the rim thickness sorting did not
produce statistical results.
Additionally, the bullet weight measurements did not produce any reliable
data. However, Eley 10x shot two
consecutive tests that strongly supported the bullet concentricity theory. Figure 2 contains the measured results of
these two bullet concentricity tests.
These tests were shot with 10 round groups. Because of the multiple tests I had prepared for, the bullet
concentricity tests were fired with bullets that all had the same 0.041” rim
thickness.
Figure
2: Bullet Concentricity Test**, Group
Diameters-inches, OTC, 50 Meters.
Bullet Concentricity |
Loose* |
.000 |
.001 |
.002 |
.003 |
|
Eley 10x, Lot EEL98, series 1 |
.360 |
.350 |
.510 |
.570 |
|
|
Eley 10x, Lot EEL98, series 2 |
.400 |
.390 |
.450 |
.570 |
|
|
Average of the two series |
.380 |
.370 |
.480 |
.570 |
|
*Loose = bullet that is physically seated loose
in the case.
VIEW ACTUAL TARGETS FROM SERIES 1
VIEW ACTUAL TARGETS FROM SERIES 2
I tested ten brands of ammunition in these 1995
experiments at the Olympic Training Center.
This lot number of Eley 10x shot the smallest groups when firing the
baseline trial. I am convinced that
this particular lot of Eley 10x produced the above groups because it was the
best harmonically balanced with my 1413 Anschutz. However, I have no evidence to prove this statement. Another important conclusion that this
testing session revealed was, only the best ammunition is worthy of testing at
50 meters or longer. Less expensive
brands of ammunition seem to have too many accuracy limiting errors, probably
due to the economics of component cost, and the speed of manufacturing used to
reduce unit expenses.
Leap forward through the next eight years of raising four kids and studying anything I could find concerning rifle accuracy. Contained within this stack of books I found the physics law responsible for how bullet concentricity effects dispersion. The challenge now was to take my meager evidence to someone with the facilities capable of proving the theory true in 22 caliber long rifle ammunition, and then convince them to help me conduct a final controlled test. This theory is not new to the firearms industry and its effect has long been battled in the design of modern target rifles and ammunition. To my knowledge, no one has ever researched this theory in 22-caliber long rifle ammunition with low ballistic coefficient lead bullets at subsonic speeds.
I am lucky enough to live in the Black Hills of
South Dakota. This area is very
firearms industry rich, and one of those companies is H-S Precision. H-S Precision is known for building very
accurate rifles, pistols, and barrels utilized by the public, law enforcement,
and the military. They are also the
originators of the aluminum chassis bedding block composite synthetic
stock. In addition, they manufacture
ballistic test barrels and equipment for all of the firearms industry. It was only natural that I chose H-S
Precision to present my evidence to, a company renowned for its’ pursuit of
accuracy. It took a little finesse and
a lot of luck, but I scored a meeting with Tom Houghton Jr., President of H-S
Precision. I presented my data and
evidence to Tom and he agreed to help me finish testing. It took over a year to get in the tunnel
because of their busy schedules and commitments. However, it was worth the wait to access this quality of
equipment.
In preparation for these tests, I had learned to
only use the best ammunition available on the market. My prototype 22 rimfire bullet concentricity gauge measures the
axial relationship of the bullet to the case.
In reality, this measurement is the statistical variance of bullet
seating during the manufacturing process.
Figure 3 shows the percentage yields of the bullet concentricity
measurements for the test ammunition. I
also added some extra brands of ammunition, just for reference.
Figure
3: Bullet Concentricity as percentage by brand.
|
Brand |
Loose |
.000 |
.001 |
.002 |
.003 |
.004 |
.005 |
.006 |
.007 |
.008 |
|
Eley 10x, 1995
lot |
14 % |
17 % |
53 % |
13 % |
3 % |
** |
|
|
|
|
|
Eley 10x |
3 % |
16% |
69 % |
12 % |
1% |
|
|
|
|
|
|
Eley Ultimate
EPS |
15 % |
5 % |
32 % |
35 % |
11 % |
2 % |
** |
|
|
|
|
Lapua
Dominator |
4 % |
6 % |
39 % |
45 % |
6 % |
|
|
|
|
|
|
Lapua Midas M |
1 % |
5 % |
37 % |
44 % |
12 % |
1 % |
|
|
|
|
|
Eley Club Xtra |
2 % |
8 % |
22 % |
34 % |
23 % |
7 % |
2 % |
1 % |
1 % |
|
|
Federal Ultra |
4 % |
8 % |
20 % |
41 % |
12 % |
11 % |
3 % |
|
|
|
|
Winchester Mk
III |
0 % |
3 % |
18 % |
27 % |
20 % |
15 % |
8 % |
5 % |
2 % |
2 % |
** = less than 1 percent of the measured
ammunition.
Loose Ţ
bullets that are physically seated loose in the case.
On to the 2004 shooting tests at H-S
Precision. The shooting tests were conducted
in one of H-S Precision’s climate controlled shooting tunnels. H-S Precision supplied a new 22-caliber
ballistic test barrel that is 2 inches in diameter, and 22 inches long. The barrel was mounted in a machine vise and
bolted to the concrete floor. Every
round was chronographed to detect any large variance in velocity, which may
influence groups. The ballistic test barrel was cleaned between every brand of
ammunition and seasoned with four rounds of ammunition at the start of each
brand. All individual test groups were fired with 20 rounds. Some of the brands were fired in progression
of the bullet concentricity and some in regression, to minimize the effect of
barrel fouling in the data.
Additionally, two of the four brands of ammunition were fired with mixed
lot numbers, this was by accident not design.
From the results of the 1995 shooting test, I had calculated that for
every 0.1 degree in base angle, there is 0.15 inch dispersion at 100 yards. This calculated slope is what I would be looking
for in the new charted data.
We suffered a couple of nights of setbacks due
to mechanical problems. But Tom was great and had them fixed in short
order. After 10 years of trials and
research I have to admit that sleep was short, very short. Finally, the third night at H-S Precision we
are shooting. However, the targets are
not very good. There seemed to be a
trend, but it is not straight line like expected or predicted. Arriving home that night disgusted, I pulled
out my dial caliper and started to measure groups anyway. Then some math, and plotting of the
data. The average slope of the
dispersion line on the graph is at the expected angle, but it is way too high. This told me that it is working, but it’s
not. It is now 2:00 a.m., I have hardly
slept in three days, and I have to be at work at 6:00 a.m. Good night.
The next day at work it hit me, there is an
error in the machine vise. That is a
logical conclusion of why the group diameters have all shifted up the graph, from
their expected smaller diameters. Well,
now I had a fun job. I had to go to Tom
that night and explain my mathematical evidence shows a problem existed in his
expensive test equipment. At least he
didn’t throw me out. We went down
stairs, and after some investigation of the machine vise, we found the left
front floor bolt was loose because the expansion nut in the concrete had pulled
out. Could that really be the error of
this 250-pound monster, shooting a 22?
We fixed the floor mounts and began to shoot again. From the first little bug hole that night,
targets poured out of the machine vise just about exactly as they were
predicted. That single loose floor bolt
was the problem, and almost ended ten years of work. Figure 4 shows the measured results of these shooting tests.
Figure 4: Bullet Concentricity Shooting Tests*, H-S Precision, Machine Vise, 2004
==== 20 round Group Diameters in
inches ====
|
Bullet
Concentricity |
Loose |
.000 |
.001 |
.002 |
.003 |
.004 |
Eley Club Xtra ** |
|
.330 |
.280 |
.390 |
.340 |
.350 |
|
Eley 10x W2B066 |
|
.240 |
.270 |
.275 |
|
|
|
Lapua Midas M |
|
.230 |
.280 |
.295 |
.315 |
|
|
Eley 10x EEL98 |
.290 |
.250 |
.270 |
.320 |
|
|
|
Eley Ultimate EPS |
.310 |
.240 |
.300 |
.380 |
.380 |
|
Average ( 80 rounds ) |
.300 |
.240 |
.280 |
.318 |
.348 |
|
** Eley Club Xtra not included in the average
group diameters or statistics.
VIEW
THE ACTUAL TARGETS FIRED IN THESE TESTS
Figure
4A: Statistics of Bullet Concentricity Shooting Test, H-S Precision, 2004.
|
Bullet Concentricity |
.000 |
.001 |
.002 |
.003 |
|
Mean |
.240 |
.280 |
.318 |
.348 |
|
Standard
Deviation |
.008 |
.014 |
.045 |
.046 |
Confidence
|
99 % |
98 % |
98 % |
95 % |
|
Confidence
Test |
.240±.002 |
.280±.004 |
.318±.011 |
.348±.014 |
|
|
||||
For those who are not familiar with a Confidence
test, the proper way to read this is;
This rifle has a 99 percent chance to shoot .000
B.C. bullets in a .240” diameter ±
.002”. (Diameter from .238” to .242”).
Everyone should be able to substitute the other three confidence tests
into this statement. I don’t think you
really need any more evidence, the bullet concentricity theory is true with
match grade 22 caliber long rifle bullets.
Following is a chart of the shooting test data
for bullet concentricity measurements.
There is a color key at the bottom of the chart. The four brands of ammunition all have their
own color code seen in the key. The
average of the four brands included in the 2004 tests at H-S Precision is shown
in heavy black. The heavy brown line at
the bottom of the chart is the expected dispersion calculated from the testing
at the Olympic Training Center. These
two equal dispersion slopes provide confirmation of the data between the two
independent tests. The reason the
shooting test groups do not go to zero is because of the other remaining errors
in the machine vise. A discussion of
how multiple accuracy influencing errors effects group diameters follows later
in this article.
