I was under the impression you can't legally buy fully automatic weapons at all. Not even Cops/Military. You can be issued a service weapon but fully auto is a no no for personal use.
They do it to eliminate the threat of civilians being able to fight tho government.
Correct me if I'm wrong, I'm going off memory of what my buddy in the air force told me.
Full auto is still legal. You must have a Class III License in order to own one. It has been illegal to manufacture or sell automatic weapons since 1986. This is why an M16 will cost you around $15,000-20,000 these days. Well... A legal one, that is. If you just want an automatic rifle, you can buy a FN FNC for around $3,000 and an auto sear for another $3,000. The advantage of the M16 lower is that it can be used with pretty much any upper. You can fire automatic 5.56, .300BLK, 6.8SPC, 6.5 Grendel, .458 SOCOM, .50 Beowulf, 9mm, etc.
Your posts should be stickied, Zenith.
Maybe I'll collect them and add links to the front page or something.
Welcome to the Rumble Strip and the Zenith's Guide to AR15's!
Here's the first part of my technical discussion on the AR15. First we're going to be covering the barrel. I'm putting this out here for the good of the community but mostly so I can have a reference guide. I'd like critiques and questions if possible. At the end I'll consolidate them into one long wall of text.
Let’s make one thing clear. You don’t need to know any of this. The best way to ensure that your AR is up to scratch is to buy your components from respected manufacturers. Companies like LMT, DD, BCM, Colt, Noveske, and Rainier Arms will give you the right stuff to make a proper rifle. Anyways, here’s my small technical guide. I will probably forget a couple of fairly important things. I might even tell you something that’s wrong. If you see any holes or flaws, let me know so I can edit this post. The surefire way to learn the platform is to read what professionals from the industry have to say and figuring it out on your own.
Barrel
I can assume almost everyone here understands the basic purpose of the barrel. Here's a small overview of the basic sections anyways.
Basic Layout of an AR15 barrel
In most cases, the barrel and chamber of a rifle are one piece, so we will operate with that assumption throughout this. Working from the chamber end, the barrel supports the cartridge in the chamber. Directly in front of the chamber is the throat, which supports the bullet as it starts its travel and guides it into the rifling. Think of it as a funnel between the chamber and the bore. This is a very key part of the potential accuracy of the rifle... if the bullet is "set" in the bore slightly crooked, it will stay that way in flight and degrade accuracy. A barrel really wears out in this throat area, even after the throat is "shot out", the bore and rifling just a few inches in front of the bore is usually still in great shape.
The rifling starts the bullet twisting or spinning. The Rate of Twist (RoT) is given as a ratio of how far the bullet must travel to spin on full revolution (360 degrees), this is normally written as 1:7 or 1/7 or One in Seven, simply meaning that the rifling makes one full turn in every seven inches of barrel.
Most of the work of the rifling is done within the first few inches. maximum chamber pressure occurs within this same length of barrel as well, and from there on the barrel simply contains the pressure and allows the bullet to accelerate faster and faster. Naturally, a longer barrel produces a faster muzzle velocity; however, there is a point of diminishing return. A barrel can be too long, the pressures start to fall as the bullet moves further down the bore and there is a tipping point where the bullet will actually start to slow down before it leaves the barrel. For the AR platform, you probably would not want to pack around a rifle with that long of a barrel through.
Conversely, shorter barrels have lower muzzle velocities. On the AR/5.56 rifles it seems that as barrels are reduced below 16 to 18 inches, the velocities start to fall off exponentially. This is highly dependent on ammo selection however, but is a good rule of thumb.
At the very end of the barrel, where the bullet leaves the muzzle, is the crown area. This end of the barrel must be as close to perfectly square as possible and free of nicks or burrs. If it is damaged or crooked, the gas pressure from the muzzle blast will bleed off on one side of the bullet first and disrupt its stability – not at all good for accuracy. This is why it is a rule when cleaning the gun to only push a bore brush through in the bullet's path, never to go from the crown to the chamber.
It is important to understand that the barrel is a long term wear item. Most major components of any gun are wear components. Your barrel will break-in then lose accuracy throughout its life until it exhibits unacceptable performance. The point at which this occurs is dependent on your standards and budgetary concerns. The US Military considers 5 MOA to be the acceptable standard for an M16. Most individuals would consider a gun that prints 5" groups at 100 yards to be junk.
Types
Let's start with the basics. The two primary types of AR15 barrel you will run into are called “Stainless Steel” and “Chrome Lined.” The names can be a bit misleading; both are made out of stainless steel. The latter is just designed to receive hard chrome. The chrome treatment is a coating 3 to 5 ten-thousandths of an inch thick.
Since the chrome coating is harder than steel, a chrome lined barrel can expect a longer service life, less wear under prolonged hard use (rapid fire), and can be more reliable under extremely adverse conditions compared to a stainless steel barrel. The advantage that stainless steel barrels have is accuracy. Chrome lining a bore can have irregularities that negatively affect their ability to shoot tight groups. How much the chrome lining actually affects accuracy is dependent on how much care and skill the person who made the barrel used. This accuracy difference is inconsequential to most people who will feed their gun M855 ball since the ammo is by far the weakest link at that stage.
As we discuss accuracy we need to remember that the barrel is just one of several components that are required to put up tight groups. These components are:
- A good barrel
- A good round
- A good trigger
- A good optic
- A good shooter
You want at least 4 out of 5 of those things for an accuracy focused gun.
According to Grant of G&R Tactical… “Typically, the SS barrel is going to give you between .5-.75 groups with the CHF barrel will shoot between .85-.1.25." with match ammunition, a good trigger, a good optic, and a good shooter. Otherwise the differences will likely be undetectable. In fact, nearly all the AR rifles in existence are capable of “practical accuracy” for a carbine, defense, battle, plinker type rifle – that is that nearly any barrel is capable of hitting a 8” target at the functional limit of the sighting system. In other words, a chrome lined barrel is more than accurate enough for most users.
If you are considering any kind of precision shooting, Stainless steel barrels start to look more attractive. Premium barrels such as a Noveske, Walther, or White Oak Armament can cost around $400. The amount of rounds it will take to shoot out one of these barrels depends on how those rounds are fired, but combat oriented users such as Pat Rogers have put over 16,000-20,000 rounds through Noveskes and Douglas when the barrel was said to be done. That is several thousand dollars of ammunition. In the grand scheme of things, the cost a stainless barrel will be a drop in the pan compared to the running cost. Taking the gun to shoot tin cans with Wolf .223 one day then go for tight groups with Mk262 Black Hills is perfectly reasonable for a Stainless Barrel.
Your barrel's life will be dictated by ammo use. Russian bi-metal jackets will wear down a gun more than double as quickly as a copper jacketed round, but will be cheaper in doing so. See this in-depth test.
http://www.luckygunner.com/labs/brass-vs-steel-cased-ammo/
The choice between stainless and chrome lined is one based on the needs for a rifle.
There are also some new coatings and treatments coming out that look to challenge chrome lining as the go-to barrel treatment. Smith and Wesson has a Melonite treatment on their barrels that is similar to the Tennifer treatment Glock barrels undergo. Instead of coating the steel like chrome lining does, Melonite directly changes the property of the steel to a depth of about .005”. According to S&W this treatment gives more durability than chrome-lined but with the accuracy of a stainless barrel.
Is Melonite the new hotness? I have yet to see any testing that can prove Smith’s claims that Melonite is superior to chrome-lining or stainless in any respect. In the case of the M&P15 AR that S&W sells, I notice that the S&W along other guns that use a similar treatment, the Bushmaster ACR and Sig556, are aimed towards the hobby crowd. None of the rifles that use the Melonite treatment are known to post particularly good groups, but this can be down to the construction of the rifle.
Materials
Moving on to construction materials, mil-spec dictates that the barrel is made with MIL-B-11595-E Chrome-moly steel with a chrome lined bore. Colt, LMT, and Bravo Company make their barrels to this spec. 4150 is also a perfectly fine steel, 4140 is used by some of the commercial. Some companies make their barrels out of better steels than Mil-spec.
For an outline of 4150 vs. 4140, I’ll quote Bill Alexander of Alexander Arms.
Bill Alexander
An examination of the chemical analysis of 4150 per AISI specifications shows that this steel is indeed an easier hardening grade but also that vanadium is not present in the alloy. The confusion in terms of barrel steel is that the correct alloy is not 4150, rather a modified vanadium bearing grade per mil specification. The presence of vanadium acts to slow the response of the steel to heat treatment but also as a grain refiner. This promotes excellent ductilty and a high Kic value.
Unless you aim to hold the barrel at a temperature that exceeds the solution temperature for the alloy ie the quenching temperature for a significant period of time, the alloys 4140 and 4150 will behave in a near identical manner. It is virtually impossible to affect the grain structure of the steel at the temperatures found within even a heavily abused weapon. However the following are considerations in the selection of barrel steel.
The 4150 CMV alloy will allow more margin for error if an overload condition occurs equally they have a much greater resistance to cracking if a heated barrel is suddenly quenched by seawater, snow, etc. This said M2 barrels have been seen with cracks running the full length following one of the rifling grooves from waves hitting a hot gun.
At extreme cold levels the properties of 4150 CMV are desirable if the material is to exposed for significant time periods. It is this cold weather feature that is the primary driver in the material selection.
The selection of essentially a specialized gun steel over a commercial AISI grade is always preferable for a safety critical part. Unless the barrel maker can undertake both chemical and microscopic examination of a "rack grade" steel it is possible that the barrel is manufactured from a coarse grained alloy. This will impact the toughness of the finished part.
With this noted buyers should beware that they are not getting what they believe is a premium barrel steel when in fact the vendor has simply used plain AISI 4150 in place of 4140.
I'd like to emphasize that just seeing the number 4150 on the spec sheet is not enough.
For stainless barrels different steel must be used. Very high levels of chromium and nickel make them resistant to rust and corrosion. The most common stainless steel used is Carpenter 416.
Methods
Cold Hammer Forging is a newer construction process to AR15’s that is good to look out for. Here is the best explanation I can give for what Hammer Forging is to the uninitiated. We put a reverse steel die inside a tube and then a really big and noisy machine uses 4 hammers on the outside surface of the tube until you’ve got a barrel. Initial tooling costs are very, very high, but per-unit costs are very low. Companies such as Daniel Defense, FN, HK, and Knight’s Armco use this process to manufacture their barrels.
The advantage of the CHF barrels is that the process actually changes the crystalline structure of the barrel. They are very hard and, if relieved properly, very accurate. The interior finish is very good and the bore surface becomes work hardened in the beating process. The result is a very durable, long lasting barrel. Modern hammer forging has progressed to the point that even the chamber can be included in the mandrel pattern. These machines are very large, complex, and expensive however. So the small custom barrel shops are pretty much eliminated from using them.
To finish up this section on barrel construction techniques, we need to talk about testing. The amount of care that goes into a barrel is far more important than you might think. High pressure testing and Magnetic Particle testing are very important for quality control and ensuring each barrel ready to rock. Commercial grade companies like S&W, Spike’s, and Bushmaster batch MP test their barrels. High end companies like Noveske HP and MP test each individual barrel several times throughout the construction process. Obviously we want our barrel to be a shining example of the design. Commercial brand AR's tend to have more flaws that must be sent back to the factory while high end shops rarely make mistakes. It's all about how much the customer is willing to pay.
Characteristics
-- Profile --
Let’s talk about barrel profile. Chances are you’ve seen that little notch that M4’s have on the barrel. That’s called an M203 cut on a Government profile barrel. Anyone with engineering know-how will also not be surprised to learn that having a cut like that is not conducive to stiffness. Government profile has the advantage of being at a “good” weight for general purpose.
Some manufacturers choose to leave out the M4 cut but use the same amount of metal as the Government profile, there are many names that are used for this, but MEDCON (medium contour) is common. Lightweight profiles should also be considered depending on your kind of shooting. They heat up faster, but also cool off faster. Most people also don’t shoot quickly enough to overheat the barrel much. Since the most noticeable weight on the gun is the weight of the barrel, shaving up to half a pound with a light weight barrel is well worth considering.
-- Chamber --
The chamber of an AR15 should be 5.56 NATO, not .223 Rem. A 5.56 chamber is bigger than a .223 to accommodate the higher pressure of the 5.56 round and for reliable feeding and extraction of a semi-auto rifle. For more information about the differences between .223 and 5.56, read this by my favorite gun-writer Andrew Tuohy
http://www.luckygunner.com/labs/5-56-vs-223/
There are also other chambers out there, usually in stainless steel barrels. Noveske uses a proprietary chamber that was designed to balance accuracy with reliability, others might use a Wylde chamber which was designed to fire match .223 and 5.56 NATO without issues.
-- Twist Rate --
Most AR-15’s will also run a 1/7 twist - simply meaning that the rifling makes one full turn in every seven inches of barrel. Original 55gr M16’s came with 1/12 twists back when they were using M193 ammo. The M16A2 upgraded to heavier 62gr M855 and a 1/7 twist. Commercial grade AR’s sometimes come with 1/9 or 1/8 twists. This used to perfectly fine, but recent developments in bullets have gravitated towards heavier 70gr+ rounds for accuracy and defense. 1/9 isn’t getting the job done as well as 1/7. If you have or can get a good deal on 1/9, don’t worry. There are plenty of options out there, especially for varmint hunters. 1/12 is rare and unsatisfactory.
-- Feedramps --
Another place to look at an AR15 is the feed-ramps. There are two kinds of feed ramps, Standard (aka M16) and M4. M4 feed ramps extend below the barrel extension and the upper receiver must be machined with the ends of the cuts. The Standard feed ramps are only present on the barrel extension. Here’s a handy graphic. This was developed to accommodate the faster cycling of the M4. There is much debate as to whether M4 feed ramps actually do anything. Speaking as an engineer, I can’t see how they make things any worse. Either option is fine as long as it matches the receiver. See graphic.
That’s the barrel portion, next up is the operating system. The rest of the rifle gets easier, promise.
