AR15 Barrel Materials and Finishes

Barrel Materials and Finishes: What to Know

There are a lot of different types of barrels on the market for the AR platform. Taking a quick peak into
descriptions and specs can reveal many different terms and phrases which can be confusing for
someone new to building ARs. In this piece, I will be going over popular options on the market, pros and
cons, and things to keep in mind for the purpose of your next build.
Types of Barrel Metal
Typically, there are two different types of barrel steel that are currently used in the production of AR
barrels. The types are either a type of stainless steel, or a type of carbon alloy chrome-moly steel. Each
have their own properties, benefits, and drawbacks.

Stainless Steels
The most popular stainless steels currently in the AR market are 410, 416, and 416-R stainless, with 416-
R widely considered to be the better material. The main difference between 416 and 416-R is that 416-R
has the addition of molybdenum and a lower content of sulfur when compared to standard 416 stainless
steel. Because of the this, it reacts better to extreme cold.
416-R is a proprietary alloy of stainless steel that is manufactured by a company named Crucible. Their
claim is that 416-R barrels can be used at temperatures as low as -40 degrees F. This may not be a worry
for people that live in Texas, but it could be a concern for the snowbirds in Minnesota or the extreme
areas of the Dakotas. At that level of cold, standard 416 steels can be unsafe to fire due to “temper
embrittlement”. We won’t get too far into the weeds, but essentially at that extreme of cold a standard
416 stainless steel becomes brittle and can potentially have a catastrophic failure.
So why would someone choose a stainless-steel barrel? There are some great benefits, namely the
machinability and corrosion resistance of the metal. Keep in mind that “stainless” is just a name though.
While it does have corrosion resistance, it is by no means perfect and can rust. As far as machinability,
this can aid in precision and, for lack of a better word, high-definition rifling. Some of the most precise
barrels on the market are made from a stainless-steel barrel because of the absolute precision of bore
and rifling. Concentricity and precise machining are king when it comes to accuracy.

Chrome-Moly Steels
Typically, the two most common chrome-moly (CM) steels used for barrel manufacturing are 4140 CM
and 4150 CMV steel. 4150 CMV steels are generally considered better than their 4140 CM counterparts,
but honestly it is marginal. Both types of steel are considered “machine-gun” steels for their attributes
of heat dissipation and abrasion resistance compared to stainless types of steel.
4150 CMV is marginally better at dealing with heat compared to 4140 CM due to the addition of a small
percentage of vanadium, hence the V. This type of steel is considered mil-spec with the specification of
Mil-B-11595E. Dealing with high heat applications, such as full-auto firing, so far, the best material for
the price is 4150 CMV steel. Keep in mind though, that 4140 CM and 4150 CMV are NOT inherently
chrome lined. The “chrome” in their name only designates that a percentage of chromium is a part of
the alloy.
Why would someone choose a 4150 CMV steel? It is a great general-purpose steel for someone that
wants a barrel that can handle a high round count and could be doing repeated mag dumps. When
properly chrome lined or nitrided, a 4150 CMV barrel can have a very long life depending on its firing
schedule. Another great attribute of 4150 CMV steel is its impact resistance. For a hard use rifle that
may see a hard life of training, 4150 CMV can be an excellent choice. Keep in mind, an unlined
parkerized 4150 CMV barrel is no more durable than stainless steel when it comes to round count.

Types of Coatings/Finishes
Adding to the confusion, there are multiple coatings, and surface finishes available for barrels on the
market. Regarding barrels, the most typical finishes are parkerizing, chrome-lining, and nitriding. Some
can be used in tandem with each other depending on type of steel, while some processes can not be
used at all.

Parkerizing

Also known as phosphate, or manganese-phosphate, this metal treatment is great at corrosion
resistance and its porous properties for taking in oil. It’s typically a black or dark grey and when oil is
applied it is effective. This type of finish has been used by the military and the firearms industry for a
long time because it is relatively inexpensive and effective.
Parkerizing is not going to be available for non-ferrous steels such as stainless, so typically the chrome-
moly steels will have it as an option. Its main drawback is that is absolutely needs oil to be effective in
more humid environments. By itself, parkerizing does not provide much for increasing service life when
compared to stainless steel barrels.

Chrome Lining

Chrome lining is a protective lining in the bore of a barrel. Chrome is well known for its corrosion
resistant abilities, its natural lubricity, and its hardness. Chrome lining of a bore drastically improves
service life and round count compared to stainless steel barrels. This is one of the reasons why mil-spec
barrels in the M16 service rifle family, or belt-fed machine guns like the M249 SAW, have chrome lined
bores.
Because of its natural lubricity and hardness, a chrome lining also helps with heat dissipation. When high
round counts are expected, chrome lining can be a great choice. Chrome lining typically only applied to
the bore of the barrel and the outside of the barrel will be parkerized. Combining the two provides a
great finish for a hard use barrel. Chrome lining, just like parkerizing, cannot be applied to stainless steel
barrels. It may not be the best option for absolute precision either. Chrome lining can have issues with
concentricity inside the bore since material is added and can change the internal dimensions of the
bore.

Nitriding

Nitriding has many names. You may see it listed as Ferritic Nitrocarburizing (FNC), Quench Polish Quench
(QPQ), Tennifer, or Melonite. Some are more proprietary than others, but they are all the same in
process. Nitriding is a case hardening process for steel which involves a salt bath at temperatures that
can exceed 1,000 degrees F. At this temperature, the nitrogen and carbon diffuse into the steel which
hardens the steel, provides excellent corrosion resistance, and can provide a low friction coefficient
which helps wear resistance.
In the case of a barrel, these attributes are excellent to have, and most companies offer nitrided barrels
due to its benefits and relatively inexpensive cost. Nitriding is also a durable finish that can be a better
choice for accuracy as it does not change the internal dimensions of the bore like chrome lining can.
Furthermore, both chrome-moly and stainless steels can be nitrided which greatly increases service life.
Nitriding is an absolute win.

The Choice is Yours
When dealing with your next barrel choice, keep in mind what the purpose of the rifle may be. There are
pros and cons with almost any choice but all of them can be a good choice unless the rifle is for a
specialized purpose. Also, listed above are rules of thumb. Barrel life is largely dictated by shooting
schedule and how hot the barrel gets. Accuracy is largely dictated by concentricity and how well the
rifling is made, and not the choice of steel. Above all, a barrel is only as good as the shooter behind the
trigger! Get out, be safe, and keep shooting!