Category Archives: AR-15

Metal Finishes and Treatments: What Do They Mean, and Why Are They Important?

“What lower will match the color of my upper?”

“Why should I buy an aftermarket trigger when I can do the ’15 Minute Trigger Job’ on my stock trigger or send it to someone for a cheap trigger job?”

“Why should I buy an upper that already has M4 feed ramps when I can do it myself with a Dremel?”

“Which bolt carrier group finish is best?”

If these exact questions aren’t being asked online or in gun stores on a daily basis, variations thereof are certainly bouncing through the minds of many AR-15 owners every day.

In order to understand the answers to the above questions, we must first understand what each finish or treatment is, and what it does. In future articles, I will discuss melonite, manganese phosphate, and electroless nickel (among others). For now, I want to cover heat treatment and anodizing. I would like to thank Tom Miller at Spike’s Tactical for much of the information (such as case hardening depth) provided below.

Case Hardening

Case hardening is a process used with steels that have a low carbon content – that is, below 0.25%. These are called “mild steels.” 8620 (carbon content of 0.18-0.23), which is used for the bolt carrier and the barrel extension, and Carpenter 158 (carbon content of 0.10), used for the bolt, are examples of this type of steel. As we read here, these steels cannot be “through hardened” because of the low carbon content – the surface layer must have its carbon content increased “by prolonged contact at a high temperature with a chemically reactive source of carbon.”

Then, the steel is heated to very high temperatures and rapidly cooled (“quenched”) at specific intervals. Because only the surface layer had its carbon content increased, only that layer reacted to the “quenching” process, and the hardening only occurred at that layer. The rest of the steel maintains its previous hardness.

Anodizing

Anodizing “is an electrochemical process that converts the metal surface into a decorative, durable, corrosion-resistant, anodic oxide finish.” It is essentially controlled oxidation, and comes in many types, classes, and colors. For the purposes of this article, discussion will mostly focus on Class II, Type III anodizing. Anodizing is used on aluminum components – namely, the upper and lower receivers, as well as the receiver extension tube. Because anodizing does not offer much in the way of lubricity, the interior of each anodized component should have a baked-on dry film lube from the factory. It does increase wear and abrasion resistance significantly – besides corrosion resistance, this is the primary reason for anodizing weapon components. Because exact shades are difficult to achieve, specifications for receivers will often call out a range of acceptable colors. Receivers from the same manufacturer and the same lot might have visibly different shades of anodizing.

Why Is Heat Treatment Important?

Although I’ll focus on the AR here, the same concepts also apply elsewhere.

So now that we have a very small understanding of each process, we can move on to their importance to the weapon system. As mentioned previously, the barrel extension and bolt carrier are case hardened – but so are parts such as the fire control group. This case hardening is generally around ten thousandths of an inch (0.010) deep – twelve thousandths for the barrel extension in the feed ramp area, and eight thousandths for the fire control group, specifically. In normal operation, with proper heat treatment, these components hardly ever wear out – generally, associated components wear out first, indirectly requiring the replacement of the unaffected components.

When heat treatment isn’t completed properly, however, bad things happen. See Failure Analysis of the M16 Rifle Bolt (V.Y. Yu*, J.G. Kohl, R.A. Crapanzano, M.W. Davies, A.G. Elam, M.K. Veach) – “The wear observed in the controlled experiment indicates the mechanism of why the corrosion pits formed near the locking lug fillet by exposing the Carpenter Steel 158 base metal to the environment. Vickers microhardness readings near the fillet region show that the bolt was not uniformly case hardened. Comparison of the microhardness readings near the fillet region and 10 mm from this region show a disparity of approximately 100 units. The softer, less carburized region near the fillet contributes to the formation of a wear area after firing just 1800 rounds.”

How can you reduce your chances of buying improperly heat treated parts? Well, for one thing, you can buy components from quality manufacturers that take the time to test and inspect – or require suppliers to certify that they inspect- each component individually.

Now, if this is more of a hobby for you, there’s nothing wrong with getting something replaced under warranty. However, if you depend on your rifle for more than just an afternoon of fun every month or so, it would behoove you to avoid cheap parts. Proper heat treating and inspection procedures are often first on the chopping block when some manufacturers look for ways to save money. An improperly heat treated bolt may fail within a few hundred rounds by breaking at the cam pin, or it may lose a lug or two a few thousand rounds earlier than it would have otherwise.

“What about the barrel extension?” you ask. Well, it’s hardened to 58-60 Rockwell (the “C” scale) to a depth of 12 thousandths where the feed ramps are located. The base metal, 8620, has a much softer base hardness. When people dremel away at the barrel extension, they are most certainly removing more than 12 thousandths of material.

“But hey,” you say, “that doesn’t really matter. It’s made of steel. It’s not going to wear out.” Well, if that’s the case, why bother heat treating the barrel extension at all? If it’s not important there, where is it important? Improperly heat treated barrel extensions can and do fail. See below:

“But the fire control group,” you say, “can’t it be improved in just 15 minutes?”

Not unless you really know what you’re doing (Some who think they do – don’t). There are countless reports of cheap trigger jobs failing – this is mainly because the layer of surface hardening was removed and the soft metal underneath exposed. These will fail – it may take 50 rounds, or 5000 – but they will fail sooner than properly heat treated (and unmolested) parts.

Again, to all those who say heat treatment isn’t important, or those who say that it might be kinda important, but still dremel and file on their rifles – I invite you to organize a group buy of non-heat treated components. You’ll save money, and you can file and dremel away to your heart’s content.

Anodized Receivers

The upper and lower receiver, among other parts, are anodized. Anodizing, like heat treatment, is quite thin – 2 thousandths of an inch total. As mentioned above, abrasion and wear resistance are the primary objectives, with corrosion resistance close behind. Even in extreme use, the Type III anodized receivers of the AR-15 will outlast many other components – the barrel and the bolt, for instance. However, when the anodizing is intentionally removed (and it only takes a moment with a Dremel to do so), the relatively soft aluminum below is exposed. As with the fire control group, this will cause premature failure – most likely after thousands of rounds have been fired, but this is far, far sooner than it would otherwise occur. An example is below:

While the factory intended the dremeled feed ramps to aid feeding, the manner in which the work was done resulted in the soft aluminum being pushed up over the barrel extension (which was, thankfully, not dremeled). Because receivers and barrel extensions are the same cost whether they have extended feed ramps or not, there’s no excuse for manufacturers to not properly match the two items without the use of hand or power tools.

Unless an issue such as overlap caused by a standard barrel extension protruding over the extended feed ramps machined into an upper is present, there is actually little pressing need to dremel in feed ramps – and this can be remedied in a much more simple manner by trading one of the components with someone who needs what you have and has what you need.

In extreme cases, the use of a dremel can cause a safety hazard (by weakening the locking lugs), as this sloppy excuse for a “feed ramp matching” job shows:

Yes, the manufacturer did try to cover up the hack job with a Sharpie or other such instrument. Here’s another angle, without the “makeup”.

Amazingly, the manufacturer saw no issue with the “work,” and only agreed to replace the affected uppers (yes, uppers) under public pressure from members of an internet forum.

What Does This Mean To Me?

Let’s face it – most ARs purchased on the civilian market will probably never see more than a case or two of ammunition in their owners’ lives. The majority of even the cheapest AR-15s will probably make it through this “service life” without experiencing the failure of a major component. Their owners will probably spend more time cleaning and looking at the rifles than they will shooting and carrying them. For these people, proper heat treatment and anodizing is not crucial. Even if a failure such as a broken bolt is experienced, having the weapon sidelinedĀ  for a week or two while a replacement is delivered is not a big deal.

On that same front, the basic transportation needs (for life) of those same people would probably be adequately met by a cheap economy car, and they would be able to survive without ever eating a 16 ounce prime rib cooked medium rare. However, at one point or another, they will probably aspire to have a nicer car, and will not eat only rice and beans for years on end. Similarly, even if an immediate and pressing need for a highly dependable rifle is not apparent, they might wish to buy a high quality rifle – and there’s nothing wrong with that.

Those who do have an immediate and pressing need for a highly dependable rifle – law enforcement officers, for example – should also seek out quality. High quality rifles will have all applicable components heat treated and anodized, and no machining will be done after those processes are complete. Many other things go in to making a quality rifle, but proper heat treatment and “unbroken” anodizing are often overlooked by potential purchasers.

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Cleaning Your AR-15 is Pretty Much a Waste of Time

I’m not the first person to say something like that.

I’m definitely not the most experienced AR shooter to say something like that (Recently, Mike Pannone published an article called “The Big M4 Myth” regarding fouling. I don’t want to claim any of his ideas as my own. If you see something that seems really intuitive, it probably came from him. In this article, I’m going to talk about the same subject, but with a slightly different approach).

And yet, the “clean your AR-15” mantra is repeated over and over, in gun stores, online, at shooting ranges, in military training, and so on.

Over the past few years, I’ve fired a number of ARs (and a number of other weapons, for that matter) for thousands of rounds without any sort of cleaning whatsoever – in most cases, I just kept adding lubricant to the weapon. Recently, as you can see right below this post, I fired close to 3000 rounds through a 5.45 AR-15 without cleaning or lubrication.

“But how?!” you say. “The AR-15 ‘defecates’ where it eats! I know this because people on the internet have been saying it!”

Well, I don’t want to spend too much time describing how the AR-15 works – Steve at Adco Firearms does a pretty darn good job here.

Self Cleaning?

What’s important to know is that the bolt is itself a piston – it even has rings just like the pistons in your car’s engine (unless you’re a Wankel fan). In other words, those rings need to have a good seal against the cylinder walls – the bolt carrier.

Every time the weapon is fired, the rings scrape carbon away from the carrier – the same goes for the bearing surface farther forward on the bolt (with the exception of the extractor, which must have room to maneuver, and therefore cannot serve as a bearing surface). Practically no carbon will build up on the areas where these components actually touch, even after thousands of rounds have been fired. This goes for the bolt carrier, too – where it contacts the upper receiver, it will be clean to the point that it appears polished.

Here are some photos to explain what I’m talking about:

Take a guess as to where the carrier contacts the upper receiver.

The contact points on the carrier are clean. Pretty much everything else is filthy. No big deal.

See all that carbon? Its presence is essentially inconsequential to the operation of the weapon.

It’s a bad photo, but you can clearly see the path traced by the extractor – rather, the path of carbon left where the extractor rides just beneath the forward bearing surface on the bolt. This bearing surface removes carbon from the rest of the inside of the carrier.

Here we see a very clear delineation between where the gas rings seal against the bolt – and where they do not.

What does all this mean?

Quite a few people are worried about carbon buildup. There are even companies that will sell you carbon scrapers – and of course, there are companies that will sell you an external piston/op-rod setup. Both have major drawbacks. Excessive cleaning can remove finishes which are important to the operation of the weapon. And eliminating the inline operating system, the “internal piston” as Armalite calls it, has a host of drawbacks that I won’t cover here and now.

The bottom line is that cleaning for the sake of reducing malfunctions is a waste of time. Cleaning may make the weapon prettier, cleaning may make you feel better – but cleaning will not drastically improve the reliability of the weapon, unless unrealistically large round counts are being considered. Even then, you would have a better chance of improving reliability simply by adding lube to the weapon, as shown by the single drop of oil in the cam pin hole of the 5.45 allowing the weapon to run for another 150 trouble-free rounds.What’s easier in the field – some lube, or a complete detail strip and scrape of every part with carbon on it?

There are reasons to clean your weapon, though – such as the corrosive primers used in surplus 5.45 ammunition, for example. Good finishes and metal treatments such as nickel boron and melonite should reduce this need, but only time will tell if it’s been eliminated.

Some people say that their AR only works when it’s perfectly clean. I say that if so, there’s something else wrong with the weapon. Some part is probably worn out – a spring, the gas rings, and so on – and needs to be replaced. Read Mike Pannone’s article for more information on that subject.

If your AR-15 is properly lubricated, and it’s malfunctioning, fouling is NOT the source of the malfunction.

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Rifle Recoil Comparison Video

In this video, I show the effects of different action springs and buffers on the three phases of AR-15 recoil, using a BCM 20″ upper for demonstration purposes.

I’ve copied the text from the video here so that you don’t have to wait 60 seconds while it scrolls by on the screen if you don’t want to.

There are three distinct phases of rifle movement immediately after an AR-15 is fired.

The first phase is what most people think of when asked to describe “recoil”. The projectile exits the muzzle, and the weapon pushes back against the shoulder of the shooter. Depending on the choice of muzzle device, the muzzle may rise, drop, or stay on target during this phase.

The second phase is when the bolt carrier group reaches its rearmost point of travel. This generally causes the weapon to push back against the shoulder of the shooter, and the muzzle to rise, regardless of muzzle device. Depending on the gas system, buffer, action spring, and other factors, this may be reduced or eliminated.

The third phase is when the bolt carrier group travels forward and stops after hitting the barrel extension. This generally causes the weapon to come forward, away from the shoulder of the shooter, and the muzzle to drop slightly. Depending on the gas system, buffer, action spring, and other factors, this may be reduced or eliminated.

In this video, the first phase is very similar throughout. An A2 muzzle device was used for all videos.

Pay attention to the movement speed and direction of the rifle during phases 2 and 3 in each of the following clips. It may help to focus on one point throughout the video – the rear sight, for example, or the muzzle device.
From the shooter’s perspective, the most desirable recoil characteristics were achieved with the carbine buffer and the Wolff reduced power spring.

Offering almost exactly the same amount of “shootability” – at least during phase 2, with slight forward movement during phase 3 – was the H2 buffer with the Tubb CS flat wire spring.

The H2 buffer offered good recoil characteristics with all springs, while the carbine buffer was excellent with the reduced power spring, as mentioned, but not nearly as good with BCM and Wolff extra power springs. It also did quite well with the Tubb CS flat wire spring.

From a reliability perspective, the H2 buffer is more desirable than the carbine buffer (although no malfunctions were experienced with any of the spring/buffer combinations). The carbine buffer/reduced power spring combination would only be desirable for competition or target shooting – but it would excel in those roles.

Do not assume that the characteristics shown here would also apply to midlength and carbine gas uppers. Even other 20″ rifle gas AR-15s would not perform in the exact same manner with the same components. Future videos will cover the carbine and midlength gas systems and how these components affect their performance.

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Carbine/H/H2/Rifle Buffers Compared

More video. This one uses some of the clips from a previous video for comparison purposes, and new videos with an H2 buffer.

I noted that the H2 seemed to definitely improve recoil characteristics when compared to the lighter buffers used in the video. Again, there were no issues with function, to include the bolt locking to the rear.

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More High Speed Video

This time I slowed the video down to 1000 frames per second and used 5.56 caliber weapons.

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AR-15 Buffer Comparison – High Speed Video

Have you ever heard a rifle manufacturer say that their weapon has been “tuned” to run a certain ammunition while maintaining excellent recoil characteristics?

Do you believe that this is achieved by some sort of magic spell?

Well, if you do, I’m sorry to tell you that you’re wrong.

These manufacturers are simply paying close attention to important factors such as gas port diameter and location, action spring rate, buffer weight and construction, chamber dimensions, and so on. They thoroughly test their weapons to ensure function and allow the end user to put rounds on target in the most efficient manner possible.

Other manufacturers simply assemble an AR-15 out of parts, using components and methods selected to minimize production costs. Testing does not progress beyond exceptionally basic function and accuracy testing (if at all). If you asked such a manufacturer what the gas port diameter of a specific model was, and what testing led them to use that diameter, their answer would probably not be very impressive.

It’s difficult to describe why function isn’t enough. In my opinion, the AR-15 is at its best when it is a system that works in harmony with itself, not simply an amalgamation of parts constantly fighting one another.

To illustrate this point, I have high speed video (well, kinda high speed) of a 5.45x39mm AR-15 using three different buffers. Function with each was what some would call “perfect”. The weapon did not malfunction due to any of the buffer changes, and most folks would be content to use a carbine buffer, because it’s cheap, and “it works.”

What they don’t realize, though, is that the weight of the buffer is not as important when the action spring, extractor spring, magazine spring, etc are all in perfectly functional condition. The weight of the buffer becomes critical when said items begin to reach the end of their lifespan (or were never satisfactory to begin with), or when the weapon has been fired for thousands of rounds without any lubrication, or when various types of ammunition are used.

As you can see, the carbine buffer allowed the bolt carrier to bounce back after making contact with the receiver extension. Many people say that this isn’t a problem unless the weapon is firing full auto. While malfunctions are not as common on semi auto, is this really something you want your weapon doing? Even the heavier 9mm buffer allowed a similar amount of “bounce” – it doesn’t have the heavy internal weights of the carbine or H buffers. The BCM H buffer, though, with its heavier (and separate) internal weights, practically eliminated the issue.

The AR-15 platform is great due, in part, to its modularity. However, this modularity also allows inefficient combinations of parts to function with one another. By understanding how each component affects overall function, the last .01% of reliability can be achieved, and recoil characteristics can be improved.

I’d like to thank Mike Pannone for making me think hard about buffer weight and spring rate again, and especially the importance of the action spring.

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AR-15 Weight Calculator

One common topic of discussion relating to AR-15s is weight.

Frequently, someone will want to know what a certain accessory will weigh, or how much difference there is between a heavy barrel and a light barrel, and so on.

I have created a very simpleĀ calculator – with links to resources from other websites – that will assist those who are looking for the total weight of their weapon. I cannot guarantee that it will be perfectly accurate, given variables relating to manufacturing processes and scale calibration, but it should provide a fairly accurate weight assessment.

It is a work in progress, so please excuse the rather boring appearance for now. More data will be added to the vuurwapenblog.com “Stock and Optic Weights” page soon.

I would like to thank 03designgroup.com (USMC03) and tacticalyellowvisor.net (rob_s) for allowing me to reference the data they have painstakingly compiled over the past few years.

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