Differences Between AR-15 Barrel Metals
Barrel Metal Types
4140, 4150, 4340 (Chrome Molybdenum)
Purpose: Hunting, Skeet, Generic Target Practice, and Military
Most but not all hunting and military firearms are made of some variety Chrome Molybdenum steel. If you buy a pre-built rifle on the market today it will typically ship with a Chrome Molybdenum barrel also know as Chome Moly Vanadium or just Chrome Moly.
There are a few reasons most rifle barrels are made of this material, the first being its ability to handle both impact and its ability to twist, also known as tensile strength. The second reason is one we all know too well, price. This type of steel is used in other markets to create car axles, roll cages, and gears. Due to the fact that is more commonly used it also has a lower cost to produce along with the fact that does not require as many rare elements.
One element that you should note is Chrome. Although all of these metal varieties contain some amount of chrome, none of them contain enough to provide corrosion resistance. This is also the reason you will find more blued rifles made of this material. The lack of chrome in the metal makes it easier for manufacturers to die it.
If you are interested in the actual breakdown of what is included in the steel to create it you can reference the SAE standards located here.
4140 vs. 4150 Steel
This has been a huge discussion since the creation of non-military rifles. Most non-military rifles will use 4140 instead of 4150 while the military strictly uses 4150 or different variations of 4150.
Which is better?
Well, to be honest, there is little difference for a general firearms owner. Is there a difference? Sure! In fact, the primary difference is that variations of 4150 can withstand an additional 100+ degrees of temperature before breaking down. This has been documented in a few DoD tests over the past two decades. You can find them here.
In reality, unless you are planning to be in a war zone and continuously fire your weapon on complete auto (which most people aren’t allowed to own) with an unlimited clip (also can’t own) then you have no reason to actually care about the difference. If you can get a 4150 for a good deal, great! But otherwise, I wouldn’t worry about it.
Purpose: Competition Shooting, Sniping
Ahh, a great steel for barrels! But it is expensive.
First let’s make it clear that 416 steel is not your standard stainless steel that you find in many items like appliances or cookware. In fact, 416 steel has the ability to be machined and rust resistant. This is due to the amount of chrome and sulfur in the steel which is not standard in regular stainless steel.
Why invest in 416 steel?
What a great question! To start the steel is rust resistant, meaning your gun will outlive you and can be passed down for generations. The next best thing about this type of steel is its ability to burnish, which limits the amount of fouling in the barrel, and makes it easier to clean. The overall best part of 416 steel is it accuracy.
Is 416 steel really that much more accurate?
Technically yes it is more accurate. There is no source on the internet that will tell you otherwise. The real questions that need to addressed are:
How much more accurate is 416 steel (stainless steel)?
Many tests have been completed to compare standard chrome moly barrels to stainless steel. In tests completed by both machines and humans, the accuracy rate increases between 1/3 to 1/4.
Note: Remember that in each of these tests it depends on the shooting device or the shooter themselves. There will always be people out there that will claim amazing feats, but for the average shooter, the statement above is correct.
What type of shooting are you doing?
This is a huge factor when considering stainless steel for a barrel! Stainless has many great benefits but has some major disadvantages as well. The two that come up most often is the wear and heat resistance. Stainless cannot sustain the same amount of rapid fire as other metals. In fact, due to the amount of chrome and sulfur in 416 steel the barrel will actually wear faster. Also, stainless steel heats up a lot faster than other metals used for barrels.
That being said we come back to the question above. If you are doing completion shooting with a finely tuned rifle and scope and are not shooting more than 5-10 shots in a grouping and are looking for accuracy then you should choose it. The same goes with snipers; it will provide a large amount of accuracy for someone that is trained to use it.
Chrome Lined vs. Non-Chromed Lined
Typically chrome lined barrels are made of 4140 or 4150 chrome moly steel. Manufacturers will take a standard barrel and line the inside with chrome to decrease feed problems and increase heat distribution and ease of cleaning.
Many of the forums get caught up on the fact that it decreases accuracy. This is correct as it is very difficult to perfectly line the inside a barrel evenly. That being said standard users will not see a decrease in accuracy with a chrome lined barrel. If you are not a competition shooter or sniper I wouldn’t worry about it. Plus, if you were a competition shooter I would use a stainless barrel anyways.
If you are a person that likes to go out and put as many rounds through your rifle as possible and shoots for fun then stick with the 4140 or 4150. If you plan to go with a 4140 or 4150 then try and get a chrome-lined barrel as it does help.
If you are looking for accuracy and precision and plan to compete or snipe than invest in a stainless barrel! Either way, it’s your money, so I say do what you want as long as you love it.