American Rifleman - March 2015 - 67

FIRING
LOADS

BENDING

CRACK
STARTS
AT HIGHEST
STRESS
POINT

CRACK STARTS
SHINY AREA
CRYSTALS APPARENT

Fatigue failures evidence common characteristics, such as those used to label the photograph of this broken firearm component (l.) The
frame of a Spanish .38-cal. revolver made by Orreas Hermanos is broken in two from cracking that originated at a stress riser (r.).

the design, especially if the original designer is no longer
in the picture and design changes are left in the hands of
an engineer less experienced with the project.
While practically every fatigue failure starts at the
surface, there is one notable exception caused by any
surface treatment process that involves heat and the
production of hydrogen. Coating processes commonly used
on firearms such as phosphating (Parkerizing), hot bluing
and chrome plating, and any preparatory cleaning baths
for these that involve acid, can all create hydrogen. The
hydrogen sinks below the surface where it locates between
the grains of the metal crystals and creates stress risers.
The hydrogen-created weak spot results in a microscopic
crack that grows under repeated loading. Fatigue
failures from this result from what is called hydrogen
embrittlement. The hydrogen can be driven out and fatigue
failures avoided if the part is baked after coating as heat
drives out the hydrogen.

Is My Gun Going To Have A Fatigue Failure?

The answer to that question is, "it depends." If that gun
you're firing was built before the late 1800s, chances are very
good. Guns of that period were principally made of wrought
iron-a material highly prone to fatigue failures. If it was
built between the late 1800s to the 1940s, the chances of
a fatigue failure are reduced, but still relatively high since
metallurgy was not as advanced at that time, and machining
methods produced rougher finishes than what is possible with
modern machines used today. Then, as now, "cut and try"
gun designers have not always been careful about eliminating
sharp notches and other stress risers in their designs.
Fatigue failures are less likely to occur from products
sold by longstanding firearm manufacturers. When I asked
Armida Oradei, the chief metallurgist at Beretta USA, what
precautions the company takes, she told me: "This type of
failure is prevented by Beretta via a meticulous selection
of the materials during the design phase, followed by a
careful analysis of all machining phases, to finally choosing
the optimal finishing processes." Beretta pays a great
deal of attention to the prevention of fatigue failures, "...
not only during all of the production phases but also to
the material surface finishing. Components are machined
with great attention in order to avoid machining marks
or stress point areas, and they are then heat-treated with
dedicated heat-treating cycles. Parts are then completed by
passing through many finishing phases such as tumbling,
polishing and sandblasting prior to advancing to their
AMERICANRIFLEMAN.ORG

final surface finishing treatment. The care taken in the
surface preparation is important not only to achieve
esthetically attractive and uniform finished components,
but also to improve surface characteristics that are of
critical importance to avoid stress concentrator areas
within the parts. Once the parts are completed, we follow
up with magnetic particle inspection on all critical steel
components of the firearm."
Mark Gurney, director of product management at Sturm,
Ruger & Co. emphasized that the company keeps a library of
materials that are highly resistant to fatigue and requires its
engineers to use only those materials. Ruger is very selective
about who makes its steel. The company insists on getting
material certifications-test reports that certify the steel
meets requirements. In the end, nothing induces fatigue
failure more than repeated cycles, so Ruger does a lot of
testing before releasing a new gun into production. Engineers
determine which parts will fail prematurely with something
they call "pyramid testing." It involves shooting a requisite
number of rounds through a large sample of early production
guns, then dropping the sample size in half and doubling the
number of rounds fired. This escalates until a few guns reach
a very high round count (for example, in excess of 20,000
rounds is not uncommon for some semi-automatic rifles.) This
same level of testing is also performed when there are design
changes to an existing gun. Whenever engineers come upon a
design, wear or fatigue problem, they do a redesign and fix it.
The company then draws out the same number of guns in the
new configuration and starts the pyramid test all over again.
It's not at all unusual for Ruger to expend 1 million or more
rounds during testing, in its quest to root out every potential
failure mode, including fatigue.

Conclusion

Oftentimes we have no way of knowing the level and quality of the stress analysis performed by the designer, which
materials were used, or how much endurance testing was
performed prior to a particular firearm's manufacture. So if
you're buying a gun-especially an older, used one-what
should you do? First, examine the parts, checking the corners
inside and out-especially in high-load areas. Are they sharp
or rounded? Look for cracks. Examine the surface finish. If
it's smooth, chances of fatigue are reduced. Then, talk to a
gunsmith and find out which parts are commonly replaced on
that model. No matter what you do, keep in mind that just
like every other mechanical device, guns can get tired and
stressed-and break.
MARCH 2015

67


http://www.AMERICANRIFLEMAN.ORG

American Rifleman - March 2015

Table of Contents for the Digital Edition of American Rifleman - March 2015

Contents
American Rifleman - March 2015 - CW1
American Rifleman - March 2015 - CW2
American Rifleman - March 2015 - Cover1
American Rifleman - March 2015 - Cover2
American Rifleman - March 2015 - 1
American Rifleman - March 2015 - Contents
American Rifleman - March 2015 - 3
American Rifleman - March 2015 - 4
American Rifleman - March 2015 - 5
American Rifleman - March 2015 - 6
American Rifleman - March 2015 - 7
American Rifleman - March 2015 - 8
American Rifleman - March 2015 - 9
American Rifleman - March 2015 - 10
American Rifleman - March 2015 - 11
American Rifleman - March 2015 - 12
American Rifleman - March 2015 - 13
American Rifleman - March 2015 - 14
American Rifleman - March 2015 - 15
American Rifleman - March 2015 - 16
American Rifleman - March 2015 - 17
American Rifleman - March 2015 - 18
American Rifleman - March 2015 - 19
American Rifleman - March 2015 - 20
American Rifleman - March 2015 - 21
American Rifleman - March 2015 - 22
American Rifleman - March 2015 - 23
American Rifleman - March 2015 - 24
American Rifleman - March 2015 - 25
American Rifleman - March 2015 - 26
American Rifleman - March 2015 - 27
American Rifleman - March 2015 - 28
American Rifleman - March 2015 - 29
American Rifleman - March 2015 - 30
American Rifleman - March 2015 - 31
American Rifleman - March 2015 - 32
American Rifleman - March 2015 - 33
American Rifleman - March 2015 - 34
American Rifleman - March 2015 - 35
American Rifleman - March 2015 - 36
American Rifleman - March 2015 - 37
American Rifleman - March 2015 - 38
American Rifleman - March 2015 - 39
American Rifleman - March 2015 - 40
American Rifleman - March 2015 - 41
American Rifleman - March 2015 - 42
American Rifleman - March 2015 - 43
American Rifleman - March 2015 - 44
American Rifleman - March 2015 - 45
American Rifleman - March 2015 - 46
American Rifleman - March 2015 - 47
American Rifleman - March 2015 - 48
American Rifleman - March 2015 - 49
American Rifleman - March 2015 - 50
American Rifleman - March 2015 - 51
American Rifleman - March 2015 - 52
American Rifleman - March 2015 - 53
American Rifleman - March 2015 - 54
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American Rifleman - March 2015 - 56
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American Rifleman - March 2015 - 58
American Rifleman - March 2015 - 59
American Rifleman - March 2015 - 60
American Rifleman - March 2015 - 61
American Rifleman - March 2015 - 62
American Rifleman - March 2015 - 63
American Rifleman - March 2015 - 64
American Rifleman - March 2015 - 65
American Rifleman - March 2015 - 66
American Rifleman - March 2015 - 67
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American Rifleman - March 2015 - 69
American Rifleman - March 2015 - 70
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American Rifleman - March 2015 - 81
American Rifleman - March 2015 - 82
American Rifleman - March 2015 - 83
American Rifleman - March 2015 - 82b
American Rifleman - March 2015 - 83b
American Rifleman - March 2015 - 82c
American Rifleman - March 2015 - 83c
American Rifleman - March 2015 - 82d
American Rifleman - March 2015 - 83d
American Rifleman - March 2015 - 82e
American Rifleman - March 2015 - 83e
American Rifleman - March 2015 - 82f
American Rifleman - March 2015 - 83f
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American Rifleman - March 2015 - 91
American Rifleman - March 2015 - 92
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American Rifleman - March 2015 - Cover4
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American Rifleman - March 2015 - CW4
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