SAR 20#2

should expect to find all (non-stainless) gun barrels and
receivers to be made of an alloy steel; nickel-steel, nickel-chrome,
or chrome-moly steel. These types of steel
contain trace amounts- usually only up to 3% by mass
of these other elements. The presence of nickel imparts
extra strength and tremendous resistance to temperature
and mechanical stresses. It is interesting to note that iron
meteorites are usually an iron-nickel alloy- containing up
to 25% nickel. That high nickel content is responsible
for the meteorite’s ability to survive entry. The presence
of chrome and molybdenum in steel alloy will increase
hardness and resilience. Plain carbon steel is too weak
and brittle or soft for firearms application. Chrome moly
steels are not resistant to oxidation and other surface
reactions to include rust and corrosion. Gun parts commercially
produced from chrome moly steel are always
encountered with a coating or treatment to inhibit surface
corrosion. The most common are blueing and parkerizing
which form protective oxide barriers on the steel. Chrome
moly steel may be coated, clad, or plated in other metals
like electroless nickel, hard chrome or newer high performance
metal/polymer matrix coatings.
Chrome moly steel is indeed the first choice of the
professional market. It is tough. It maintains strength and
stability over a wide temperature range. It resists fatigue
and failure caused by abrasion, wear and heat. Even in
hostile maritime environments, today’s material science
offers a host of treatments and coatings to protect the
steel from surface attack. Chrome moly used in ordnance
is not a “free machining alloy”, that is, it is difficult to machine
and form. However, chrome moly does lend itself
well to the application of these aforementioned coatings
and surface treatments. We are all familiar with “chromelined”
barrels. Most all gun barrels in general circulation
with our armed forces- pistol and rifle alike are chrome
lined (M-16 rifle, M9 sidearm). Adding a layer of abrasion
and heat resistant hard chrome to the interior surface
of a barrel adds longevity. In the case of the M16 or
AR-15, if it is respected and not abused, a chrome-lined,
chrome-moly steel barrel can expect to serve its owner
with good function and acceptable accuracy up to or beyond
twenty thousand rounds.
Stainless steel is rapidly becoming the default material
used by barrel manufacturers. The most common alloy
used in the gun market is known as 416R. This stainless
steel makes an attractive barrel to be sure. It’s bright and
shiny, and is known for being easy to machine. 416R is a
“free machining alloy” which implies that it is created with
a molecular structure that makes the material easy to cut.
Free machining alloys employ trace amounts of lead and
sulfur to improve machinability. While making this steel
cost effective to manufacturers, and visually attractive
to the consumer, the mechanical properties of free-machining
alloy may also make it less desirable to the
well-informed. 416R is not nearly as abrasion resistant
as chrome-moly steel. And it can only claim 65,000 psi
tensile strength (4140CM boasts 98,000psi). 416R does
not resist fatigue and erosion from exposure to high heat.
WWW.SMALLARMSREVIEW.COM 83 SAR Vol. 20, No. 2