The early AR type rifles were developed in the 1950s by Eugene Stoner while working with the Armalite Division of the Fairchild Engine and Airplane
Corporation.
An early "AR" rifle was the AR-10, chambered for the 7.62mm NATO round (same as the .308 Winchester). The AR-10 was not a commercial success and was
never produced in great numbers.
Later design efforts produced the AR-15, a semi-automatic rifle chambered for the smaller 5.56mm round, which is essentially the same as the .223
Remington. Armalite could not persuade the US military to adopt this early AR-15 design, and so the company fell into financial difficulty.
Therefore, in 1959 the patent was sold to Colt. Despite a change of ownership, the "AR" prefix stuck and, as the rifle gained fame and became a
commercial success, it became known as the "Colt AR-15". (Some people believe the "AR" stands for "Automatic Rifle"... it actually stands for
"Armalite").
The USAF first ordered the rifle in a select fire configuration (semi-automatic or full automatic) in the 1960s and designated this rifle as the M-16.
Other service branches quickly followed suit and adopted the M-16 as their standard battle rifle.
Its distinctive appearance became well known to the public during the Viet Nam War. Over the last forty years both the civilian AR-15 and its military
brother, the M-16, have continued to be refined and improved.
Patents expire after about 20 years, and the AR-15/M-16 patent, owned by Colt, did just that. Therefore, many other companies now make the
AR-15 and M-16, with no loss in quality.
Current production M-16s do not have a full auto option... only a semi-auto mode and a "burst fire" mode, where three rounds are fired with each pull
of the trigger.
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Design of the AR-15/M-16 Rifle
The AR-15 rifle was unique in its design as it used an unusual system to cycle the action. Traditional gas operated semi-autos (or full autos) have a
tiny hole drilled in the barrel near the end... as the bullet passes this hole, the gas pressure behind the bullet is funneled through the hole and
into a piston, which strikes an operating rod, which strikes the bolt, and cycles the action. This is known as the "gas-piston" system, and was used in
the US M-1 Garand, and the US M-1 Carbine during World War II.
However, in the AR-15 (and the M-16) the gas, after passing through the hole in the barrel, is funneled down a long aluminum tube, which ends right at
the bolt carrier... the gas is blown directly into the bolt carrier key, with no piston involved. This reduces the number of moving parts, but also
means the bolt can get pretty hot, and dirty with soot, on repeated firing. This system is known as the "direct gas impingement" system.
The .223 Remington vs. the 5.56mm NATO Round
The commercial .223 Remington round and the 5.56mm NATO military round are nearly identical, but the 5.56mm case is slightly thicker and the 5.56mm
develops higher chamber pressures than the .223.
In addition, rifles chambered for the .223 Remington and the 5.56mm have slight variations in their chamber dimensions. A rifle chambered for the
5.56mm handles either round, whereas a rifle chambered in .223 can fire, but should not fire, 5.56mm ammunition. That is why even
civilian AR-15s are routinely chambered in 5.56mm and not in .223. For example, Rock River Arms, a leading maker of high quality AR-15s, advertises its
guns as having a "5.56mm NATO chamber for 5.56mm and .223 caliber".
It is said that firing a .223 in a 5.56mm results in a very slight loss in accuracy due to the 5.56mm's longer leade (the part of a firearm's barrel
just in front of the chamber where the bullet travels before contacting the rifling). However, such a loss is probably imperceptible to most shooters.
Anyone buying an AR-15 should make sure it is chambered in 5.56mm if they wish to shoot either .223 Remington or 5.56mm NATO ammo in it.
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Field Stripping the AR-15
Here is the proper method for field stripping the weapon for cleaning or lubrication. Under normal circumstances you will not need to disassemble the weapon beyond what is discussed here.
Safety First... steps #1 through #5.
Remove the magazine, if any.
Press on the bottom of the bolt catch and maintain this pressure.
While maintaining pressure as in #2, sharply draw the charging handle all the way to the rear... this will lock the bolt open and cock the hammer... this will also eject any round that may have been in the chamber, and will also open the dust cover, if it was closed.
At this point you do not need to hold pressure on the bottom of the bolt catch any longer... the forward pressure of the bolt (powered by the recoil spring) will hold the bolt catch in place and will keep the bolt locked back.
Now push the charging handle all the way forward until it locks into place... the bolt will remain open.
Look into the chamber through the dust cover opening and verify that there is no round in there.
Now we want to let the bolt forward. You could do this by slapping the top of the bolt catch, which will cause the recoil spring to slam the bolt home, but I don't think it's a good idea to slam the bolt home on an empty chamber, so we'll do it another way.
Pull the charging handle all the way to the rear (which will release the bolt catch), and then "ride" the charging handle all the way forward and let it lock. This action closes the bolt... the hammer remains cocked.
Put the safety on... this is not actually necessary, but I like to do it since we're going to have the lower receiver lying around with the hammer exposed and cocked... I would hate to have the hammer smash my finger while I'm fooling around with the lower receiver.
Push the rear takedown pin all the way out as far as it will go. This releases the rear of the lower receiver... you can now partially rotate the upper receiver away from the lower receiver.
Push the front takedown pin all the way out as far as it will go... be careful... the lower and upper receivers will separate, so make sure you've got a grip on both parts. Work the upper receiver up and down slightly to remove it from the lower receiver. You now have the gun in two parts... the upper and lower receiver.
Note... it is not completely necessary to do #9... some people clean the gun with the front takedown pin still in place, and it can be done, but I find it awkward, and I can't do as good a job of cleaning with the two parts connected, so I separate them.
On the upper receiver... grab the charging handle and pull it to the rear... this will pull out the bolt (actually the "bolt carrier group"). Set the bolt carrier group aside.
Remove the charging handle and set it aside. You will have to work the charging handle out by lining up the two little protrusions on the charging handle with the two slots on either side of the channel inside the upper receiver.
Now we'll take the bolt carrier group apart.
On the left side of the bolt carrier use some type of tool (or the sharp point of a 5.56mm full metal jacket bullet) and pull out the small cotter pin.
Lightly tap the base of the bolt carrier on a surface and the firing pin will fall out.
Push the bolt in all the way (farther into the bolt carrier)
Rotate the small rectangular piece (the cam pin) that lies just below the bolt carrier key 90o in either direction, then remove that part... it will just about fall out.
Now pull the bolt out the front of the bolt carrier. You now have the bolt carrier group broken down into five parts.
That's all there is to field stripping the weapon. You can now clean and lube the parts as needed.
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Reassembly of the AR-15 (from a Field Strip)
While we have the bolt carrier group apart, there is one thing we ought to look at.
There are three gas rings surrounding the rear of the bolt. These rings help to form a seal between the bolt and the bolt carrier to prevent gas
leakage during firing... that is why the bolt feels a little "tight" when you pull it out of the bolt carrier.
These three rings do not individually form complete circles... each ring has about a 5% gap in it.
To work properly these gaps must be spaced out around the bolt's circumference. If these three gaps "line up", gas can leak through the opening,
causing a malfunction.
Therefore... while you have the bolt carrier group apart, it is a good idea to inspect the position of the gas rings in the bolt and, if necessary, to
rotate each ring so that, ideally, they are positioned about 120 degrees (1/3 of a circle) apart.
Now we'll put the bolt carrier group back together.
Slide the bolt into the front of bolt carrier and rotate it so that the hole in the bolt lines up with the hole in the top of the bolt carrier.
Look at the bolt from the front... you will see a small spring loaded round part (the ejector) that ejects the shell upon firing. The ejector must be at about 4:00 o'clock as you look at the bolt from the front... if the ejector is closer to 10:00 o'clock, just rotate the bolt 180°... then the hole in the bolt and the hole in the bolt carrier will be properly aligned.
Push the bolt almost all the way in, making sure the holes are lined up properly as in #1, then insert the cam pin through the hole in the bolt carrier... push it all the way down and into the bolt.
(Note... if you have the bolt rotated wrong in #1, the cam pin will not fit through the hole in the bolt... that's a safety measure to help you get the bolt oriented correctly inside the bolt carrier).
Now rotate the cam pin 90° in either direction so that its "long" side is at a 90° angle to the bolt carrier... then pull the bolt all the way forward.
Double check to make sure the cam pin is correctly oriented, then slide the firing pin all the way in from the rear of the bolt carrier... make sure it goes all the way in, and hold it in if you need to before doing the next step.
Insert the cotter pin through the hole in the left side of the bolt carrier... push it all the way in.
To check that you've done this right, push the bolt all the way in, then push the base of the firing pin forward and you should see the tip of the firing pin sticking out of the front of the bolt.
If you don't see this, you did not push the firing pin in all the way in step #4... the firing pin will fall out when you try to reassemble the rest of the gun, and even if it doesn't fall out, the gun will not fire... so make sure this is right.
Now we'll reassemble the rest of the gun.
Turn the upper receiver upside down... you will see two small slots near the rear of the channel in the upper receiver... slip the two little protrusions on the charging handle into these slots.
Slide the charging handle in slightly... don't push it very far forward... leave about 3/4 of it sticking out the rear of the upper receiver.
Pick up the bolt carrier group and pull the bolt all the way forward... just pull it out. The bolt carrier group will not fit into the gun unless the bolt is all the way forward.
Now fit the bolt carrier group into the charging handle... the bolt carrier key goes directly into the channel in the charging handle... then slide the whole thing forward into a closed position. The charging handle will lock into position, but the bolt carrier will not... it may slide out if you tilt the upper receiver too much.
Turn the upper receiver back over (right side up) and mate up the upper and lower receiver by means of the front takedown pin... be careful... work it in easy and get them into the correct position, then push the front takedown pin closed.
Now be careful here... make sure the bolt carrier group is all the way in... you may have to hold it in... then hold the upper receiver steady and rotate the lower receiver back up and into place. Press the two parts together to make sure the holes are lined up, then close the rear takedown pin.
(It's better to hold the upper receiver steady and rotate the lower receiver into place than the other way around, because it lessens the chance that the bolt carrier will slide out).
The gun is still cocked, so let's relieve the pressure on the hammer spring, so we don't put the gun away cocked. (It probably wouldn't hurt it if you did, but I don't consider that the proper way to store any gun).
You could just disengage the safety and pull the trigger, but that's not a good way to do this. Instead, do this...
Disengage the safety... then pull the charging handle part way to the rear until you feel the bolt carrier just touch the hammer... you can feel this. Then, while holding the charging handle rearward (with the bolt carrier touching the hammer), pull the trigger and let the hammer down easy. The hammer will "ride" down with the bolt carrier as it closes.
This avoids snapping the hammer on an empty chamber, which, in truth, probably wouldn't hurt the weapon, but I just don't like placing unnecessary stress on any part of a gun.
Close the dust cover.
Your gun is now in this state...
No magazine in, and chamber empty
Bolt forward, and charging handle closed and locked in place
Hammer down
Safety off... (if the hammer is down, the safety must be off... you cannot put the safety on unless the hammer is cocked)
Dust cover closed
This is how the gun should be when you're ready to store it.
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Loading the AR-15
By "loading" I mean getting the gun ready for immediate action... a full magazine inserted, chamber loaded, hammer cocked, safety on, and dust cover closed.
There are two ways to load the gun... one, in my opinion, is better than the other. I will explain both ways and explain why I think the second way is better than the first.
In each case we start with the gun in "storeroom" condition... no magazine in the gun, bolt closed, hammer down, safety off, and the dust cover closed.
Loading procedure #1...
Insert a loaded magazine into the weapon.
Pull the charging handle all the way back and let it go... let it "fly" forward at full speed. (This also cocks the hammer).
Put the safety ON.
Close the dust cover.
You now have the gun ready for immediate action... a full magazine inserted, one round in the chamber, hammer cocked, safety on, and dust cover closed. (The dust cover will open automatically whenever the bolt goes rearward, whether by firing or by pulling the charging handle back).
Loading procedure #2...
Press down on the bottom of the bolt catch and maintain this pressure.
While maintaining pressure as above, draw the charging handle all the way to the rear, then push it forward and close it. (The bolt is now locked open and the hammer is cocked... you can now release pressure on the bolt catch - the bolt stays locked open).
Put the safety ON.
Insert a loaded magazine.
Slap the top of the bolt catch... the bolt slams home and loads a round.
Close the dust cover.
The gun is now ready to fire and in is exactly the same state as at the end of procedure #1 as shown above.
So why do I think #2 better than #1? Here are three reasons why...
In loading procedure #1 when you pull the charging handle back and let if fly home, you have loaded a round into the chamber with the safety off. You now, at least for a few seconds, are holding a weapon with a loaded chamber and a cocked hammer, with the safety off... not the best idea.
In procedure #2, the safety is on before you insert a loaded magazine into the weapon. By the time you let the bolt slam home to load a round into the chamber, the safety is already on. (Remember you can't engage the safety until the hammer is cocked). In #2 there is no time during loading, not even one second, when you are holding a loaded weapon with the safety off.
In #1, when you let the charging handle go, you are causing the bolt to "pull" the charging handle along with it as it closes... which it can do very well, but it does make for a slightly less clean bolt closing. In addition, if you accidentally "ride" the charging handle forward, the bolt may not close completely and you might not realize it... and if the bolt is not fully closed, the gun will not fire. (If you see that the bolt is not fully closed, you can use the forward assist to close it).
In #2, when you slap the top of the bolt catch to release the bolt, the charging handle is already closed and does not have to be "pulled" along with the bolt carrier as it closes... this makes for a more positive bolt closing.
In #1, when you insert the magazine in the gun (with the bolt closed) you must push up a little harder to seat it since the top round in the magazine (powered by the magazine spring) is bearing against the base of the bolt carrier. If you're not careful this introduces the slight possibility of the magazine not being fully seated.
In #2, when you insert the magazine (with the bolt locked open) the top round in the magazine does not bear against anything... therefore there is no resistance offered by the bolt carrier, and the magazine snaps in easier (and more reliably).
Firing the AR-15
The AR-15 is a semi-automatic rifle, while the M-16 has two modes of fire... a semi-auto mode and a "burst" mode, where the gun fires three shots with each pull of the trigger.
We will discuss the semi-auto firing sequence only to gain a basic understanding of how the firing mechanism works.
After the chamber is loaded as above, the safety is disengaged and the trigger is pulled. Several things then happen...
The sear, which bears directly against the hammer, releases the hammer, which is driven forward with force by the hammer spring.
The hammer strikes the rear of the firing pin, driving it forward.
The forward tip of the firing pin drives into the primer, located at the base of the round in the chamber, firing it, which causes the powder inside the shell casing to ignite.
There is an internal explosion inside the shell casing, which drives the bullet down the barrel. The bullet undergoes a tremendous acceleration, moving from zero to about 3200 feet per second over the next twenty inches (in a 20 inch barrel).
As the bullet passes the gas block (the tiny hole drilled inside the barrel near the end), some of the gas pressure behind the bullet is channeled back down a long tube and blows directly into the bolt carrier key, which is mounted on top of the bolt carrier. This forces the bolt carrier to the rear.
As the bolt carrier moves rearward, the bolt (situated at the front of the bolt carrier) is rotated by means of a cam located in the bolt carrier... this rotation causes the locking lugs milled into the bolt (which mate up with lugs milled into the breech) to unlock, thus allowing the bolt to be pulled rearward along with the bolt carrier.
The dust cover is spring loaded... if it is closed, the rearward motion of the bolt carrier will pop it open, and it will stay open until you close it.
As the bolt moves rearward, an extractor (a small part on the face of the bolt that grips the rim of the shell) pulls the empty shell out of the breech and pulls it rearward along with the bolt.
As the bolt carrier moves rearward, a spring mounted ejector in the face of the bolt applies pressure to the left side of the shell casing, causing it to fly out the right side of the gun (through the dust cover opening).
As the bolt carrier continues rearward, it encounters the hammer and recocks it. A disconnector grabs the base of the hammer, requiring you to let up on the trigger and pull it again before the next shot can be fired.
The force of the gas blown into the bolt carrier key sends the entire bolt carrier group slamming rearward all the way into the butt of the weapon,
compressing the recoil spring.
The force of the gas blown into the bolt carrier key sends the entire bolt carrier group slamming rearward all the way into the butt of the weapon, compressing the recoil spring.
While the bolt carrier group is at its rearward most point (inside the butt, with the recoil spring now fully compressed), the magazine spring pushes the next fresh round upwards into line with the bolt carrier.
As the recoil spring forces the bolt carrier forward again, the next fresh round is picked up by the advancing bolt and slammed into the breech of the weapon. As the bolt closes, a cam device located inside the bolt carrier causes the bolt to rotate into a locked position... the next round is now loaded and ready to go. You can pull the trigger again (as fast as you can) to continue firing.
When you fire the last round in your magazine, the magazine spring pushes the magazine follower upwards, where it encounters the inside of the bolt catch, forcing it upwards (which moves the bolt catch in the same direction as if you pushed on the bottom of the bolt catch from the outside of the gun).
The inside of the bolt catch, now pushed into line with the bolt carrier, stops the bolt carrier from advancing and locks it to the rear.
You can now eject the empty magazine, and insert a fresh one... the bolt carrier is still locked to the rear at this point. All you have to do now is simply slam your hand against the top of the bolt catch to release the bolt.
The bolt will fly forward and pick up, and chamber, the first round out of the magazine... the safety is still off, so you're ready to keep firing.
Unloading the AR-15
When you are finished shooting, you'll need to unload your AR-15. This, like loading, must be done in the safest way possible. (The weapon should be cleaned and lubricated after shooting, but we will not discuss that here).
When you finish shooting, you will either have a round still in the chamber (if you don't fire the whole magazine) or the chamber will be empty (if you have fired up the entire magazine).
A. If you have not fired the entire magazine there is still a round in the chamber, the bolt is closed, and the gun is cocked (there may or may not be any rounds still in your magazine).
Remove your finger from the trigger guard and put the safety ON.
Remove the magazine.
Press down on the bottom of the bolt catch and maintain this pressure.
While maintaining pressure as in #3, sharply draw back the charging handle all the way to the rear... this will eject the round in the chamber and will also lock the bolt back. You can now release pressure on the bolt catch... the bolt will stay open. The charging handle will stay to the rear.
Visually inspect the chamber to verify it is empty.
The charging handle is still sticking out of the back of the gun... pull it back slightly (to release the bolt catch), then "ride" the charging handle forward to close it and the bolt... you could just let the charging handle "fly" and let the bolt slam home, but I just don't like doing that on an empty chamber. (At this point the hammer is still cocked).
Now to relieve the pressure on the hammer spring, put the safety OFF, then pull the charging handle back until you feel the bolt carrier just touch the hammer. Then pull the trigger and ease the charging handle forward until it closes and locks. The hammer will "ride" down with the bolt as it closes.
Close the dust cover... the weapon is safe to store.
B. If you have fired the entire magazine there is no round in the chamber, the bolt is locked to the rear, and the gun is cocked. Still, you never assume the chamber is empty.
Remove your finger from the trigger guard and put the safety ON.
Remove the magazine.
Visually inspect the chamber to verify that it is empty.
Pull the charging handle all the way back (to release the bolt catch), then "ride" the charging handle forward to close it and the bolt... you could just let the charging handle "fly" and let the bolt slam home, but I just don't like doing that on an empty chamber. (At this point the hammer is still cocked).
Now to relieve the pressure on the hammer spring, put the safety OFF, then pull the charging handle back until you feel the bolt carrier just touch the hammer. Then pull the trigger and ease the charging handle forward until it closes and locks. The hammer will "ride" down with the bolt as it closes.
Close the dust cover... the weapon is safe to store.
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