SAR 20#2

At high heat levels- those commonly encountered
in military applications, 416
can distort, lose its heat treated state,
and even de-alloy—a condition where
the additive materials lose their microscopic
bonds to the iron/carbon structure.
So this material, while in use, could
become unsuitable or even unsafe. Not
to worry—416R comes with a reliable
programmed response to imminent failure.
It will split like a banana peel before
it fragments. This splitting action
is resultant of the “stringers” as they’re
called, the areas of sulfur that co-mingle
in-between the regions of martensite
(crystalline structures) in the metal alloy.
There are other grades of stainless one
might encounter in barrel making. 410,
420 and 17-4 are less common, though
they are found in use. 17-4 is renowned
as a super alloy. It is fabled to get stronger
from heat exposure. It has been said
that it possesses mystical powers to
“self-heal” micro fractures and surface
defects. Few have ventured to deepdrill
and cut rifling into a chunk of 17-4.
Many have failed. The name Noveske
will forever be remembered as one that
succeeded. 17-4 is mainly used in pistol
and revolver frames, muzzle devices,
or small parts and even receivers and
bolts of custom high-end high-power rifles.
The last stainless worth mentioning
here is 410 alloy. It is the underachiever
of the bunch. The yield of this material is
actually less than its intended operating
threshold- a fact that some in the industry
will argue. 30,000 PSI is where 410 can
undergo “plastic deformation,” that is, be
stressed past its ability to bounce back.
Barrel makers still use this stuff knowing
that a 5.56 NATO cartridge reaches
over 60,000 psi just after ignition. Is this
cause for alarm? Not really. Stress is
calculated as a constant applied force.
The pressure curve inside a gun barrel
in not contained for any period of time,
nor at a static load, but rather a burst
that reaches a peak pressure. The pressure
is not contained long enough or focused
at a singular point where it could
cause damage to the barrel. The barrel
is saved by the fact that high pressure
gas acts with equal force on all sides
of its container (in this case the barrel)-
and one side of the container (the bullet)
is moving away from this applied force.
So the bullet is effectively a valve that
allows the pressure to escape. 410 alloy
is said to be tougher and more abrasion
resistant than 416. It is used by some
manufactures to make gun barrels to
save cost as it is imminently easy to
machine. The more common stainless,
416R does deliver on some promises.
Many custom rifle builders who work
for the competition market trust 416R.
Countless benchrest, palma and F-class
records have been claimed by guns fitted
with barrels made from 416R. This
material does in fact make for a perfect
surface finish during machining. This
perfect surface lends itself to superb accuracy.
A barrel properly ‘smithed from
416R will perform supremely, though
not indefinitely. A match-grade stainless
barrel fit to a high-powered competition
rifle may be expected to have
a good service life of 3000 rounds,
more or less, depending somewhat on
the caliber of the rifle, and largely on
how it is cared for.
Steel of any alloy may be encountered
in a number of “states.” This refers
to the condition of heat treatment it may
have received. Annealed steel has been
softened. This condition does not imply
that the steel is mild- only that it has been
reduced to a softer state to make it more
workable. Hardened steel generally refers
to a surface hardening to improve
that steel’s wear resistance or reduce
its frictional coefficient. This condition
may also be called “case” hardened.
Heat treated steel is generally hardened
throughout, also known as “core” hard.
Core hard is a condition commonly employed
on high wear or high load components.
Certain alloys are better suited
SAR Vol. 20, No. 2 84 MARCH 2016