AR-15 / M-4



“…a pretty good gun, even if it’s goofy looking.”

– Colonel Hal Moore, United States Army –



Introduction to the AR-15

How the AR-15 Works

Direct Impingement vs. Gas Piston

What is Mil-Spec?

Tiers of Quality

5.56mm /.223 Caliber Barrel Twist Ratios

Ammo in the AR-15

AR-15 Parts

Fieldstripping, Cleaning, and Lubrication

Five Most Common AR-15 Problems


Aluminum “G.I.” Magazines

Polymer Magazines

Super High-Capacity Drum Magazines

Backup Iron Sights (BUIS)

Shooting with Iron Sights



Introduction to the AR-15:


Wikipedia article on the AR-15 Rifle

Wikipedia article on the M-4 Rifle

Wikipedia article on the military M-16 Rifle’s AR-15 Forum Official Picture Thread .com’s M-4 Picture Thread



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How the AR-15 Works:



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Direct Impingement vs. Gas Piston:


Direct Impingement:

Direct Impingment Wiki

Direct impingement is a type of gas operation for a firearm that directs gas from a fired cartridge directly into the bolt carrier or slide assembly to cycle the action.


Gas Piston:

Coming soon.



Coming soon.


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 “Say hello to my little friend!”

– Tony Montana, From the Motion Picture Scarface –


What is Mil-Spec?


Most AR-15 rifles look the same, however in terms of engineering and precision craftsmanship their quality varies greatly. There are very few that actually meet all of the qualifications to be considered 100% “mil-spec”.

Government agencies test out a rifle system before trusting their agents’ lives to them. Most can take the abuse. Some can not.



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Tiers of Quality:


Explanation of Desirable Features in Commercial M4 Pattern Carbines

Commercial M4 Manufacturer Poll


Below is a list of most of the major players in the AR-15 manufacturing game.  The “tier one” guns are made to “mil-spec” and are certified tough enough to be used by our nation’s armed forces.  The second list is very high quality rifles, that while not necessarily meeting each and every part of the military specification, are still considered tough enough to be used by some of our nation’s finest law enforcement agencies and departments, as well as civilian contractors operating abroad.  Any rifle from these manufacturers should serve you well in a defensive role.  The last list is lesser quality manufacturers.  You should avoid these and use your hard-earned money to invest in what the professionals use.


Tier One AR-15 Rifles:

Serious fighting gear, meets or exceed the stringent mil-spec requirements of the U.S. military.


Tier Two AR-15 Rifles:

Excellent quality, but without the price of the Tier One rifles.

  • Bushmaster  (Rifles older than 3 years old.)
  • Rock River Arms (Used by the DEA.)
  • Smith & Wesson (Used by many law enforcement agencies.)
  • Palmetto State Armory (Many parts are made at the FN Herstal plant in South Carolina.  I don’t know enough about the origin, manufacturing process, or final assembly to place them in the coveted Tier One category, but I have only heard good things about these rifles.)


Tier Three AR-15 Rifles:

Entry level.  An economical way to start learning the AR-15.


Unknown or Junk:

Stay away from.  You have been warned.

  • Bushmaster  (Those manufactured in the past three years since Remington acquired them.  They are made by different people and different machinery than the original Bushmaster.  The new guns are only are similar in namesake.  They may be better than the original, or they may be horrible.  It is too early to tell.  Because there are so many quality manufacturers with proven track records, stick with one of those listed above.)
  • Bushmaster’s Carbon-15  (Regardless of when it was manufactured.)
  • Interarms
  • AR Star
  • Olympic Arms



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Ammo in the AR-15:



Wikipedia article on the 5.56mm NATO cartridge FAQ’s About Ammo

Savannah Arsenal’s Steel Case / Bi-Metal Ammuntion: Is It OK To Shoot In Your AR-15?


The Difference Between .223 Remington and 5.56mm:

  • .223 Remington:  One of the most popular rifle cartridges among American shooters.  Optimized for accuracy (varmint hunting).  Can be used in 5.56mm barrels.  While similar to NATO-standardized 5.56×45 ammo, .223 and 5.56 rounds are not identical, so be sure you’re shooting the appropriate caliber in your firearm.
  • 5.56mm NATO:  Optimized for reliability (military).  Loaded at higher pressures than .223 ammo.  Pressure too high for .223 Remington barrels.
  • It is safe to shoot .223 Remington out of a 5.56mm barrel, but you shouldn’t shoot 5.56mm out of a .223 barrel.


Military Ammo Designations:


  • M193:  5.56×45mm 55-grain ball cartridge.
  • M196:  5.56×45mm 54-grain tracer cartridge, red cartridge tip.
  • M855:  5.56×45mm 62-grain FN SS109 ball cartridge, green tip w/steel penetrator and a lead core.
  • M856:  5.56×45mm 64-grain FN L110 tracer cartridge.
  • M262:  5.56×45mm 77-grain Open-Tipped Match/Hollow-Point Boat-Tail cartridge. Mod 0 features Sierra Matchking bullet, while Mod 1 features either Nosler or Sierra bullet.


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5.56mm / .223 Caliber Barrel Twist Ratios:


 Gun & Ammo’s The Spin on .223 Twist Rates



  • This means that the bullet will make one complete rotation for every seven inches that it travels down the barrel.
  • This is the fastest twist rate that you will encounter on production AR-15 rifles.
  • Manufactured originally to stabilize the heavier SS109/M855 ball and M865 tracer ammo.
  • Good twist if all you are planning on shooting is 62 grain ammunition.
  • This is the twist ratio of a mil-spec AR-15.



  • This means that the bullet will make one complete rotation for every nine inches that it travels down the barrel.
  • Good all around twist ratio.
  • Best suited for 52-69 grain ammunition, but either end of the envelope will be questionable.
  • Good for shooting either 55 grain or 62 grain military ammunition.
  • Seen on many commercial-grade AR-15 rifles.



  • This means that the bullet will make one complete rotation for every fourteen inches that it travels down the barrel.  This is a slow twist rate.
  • Originally used on the early M-16 / AR-15 rifles with 55 grain ball ammunition.
  • Understabilizes heavier ammunition and will affect accuracy.
  • Creates a tumbling effect upon bullet impact. IMHO, better to shoot straight with a good HP bullet as your chances to hit are better and damage will most likely be greater.
  • If you have an older rifle with this twist, stick to 55 grain ammunition.


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AR-15 Parts:


AR-15 Parts Diagram:

M4 Parts


AR-15 Lower Parts:

AR15 Lower Receiver Parts


AR-15 Bolt Carrier Group:

AR15 Bolt Carrier Group 1


Types of Bolt Carriers:

Bolt Carriers


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Fieldstripping, Cleaning, and Lubrication:


Cleaning & Maintenance:’s AR-15 Hacks: Destroying 4 AR Maintenance Myths


How To Fieldstrip the AR-15:’s How To Field Strip the AR-15



How to Clean and Lube the AR-15:

  • Scrub chamber & locking lugs.
  • Scrub bore from the chamber end.
  • Strip bolt assembly from carrier.
  • Make sure carrier key is tight.
  • Clean gunk out of upper.
  • Lube everything.
  • Hose out lower with degreaser.  Lube moving parts.
  • **Check gas ring friction.  Extend bolt from carrier and stand the assembly on its head.  If the weight of the carrier causes the assembly to collapse, you need new rings.
  • **Most important:  Keep chamber and locking lugs clean.



How To Remove A Stuck Case From The Chamber Of Your AR-15:



AR-15 / M-4 / M-16 Operating Manuals in PDF:


Armalite-AR10-M15 Manual PDF

Bushmaster Manual PDF

US Army M-16 Manual PDF

US Army M-16 Technical Manual PDF


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Five Most Common AR Problems:


Insufficient extractor tension:  Causes cases to be left in the chamber or dropped loose into the feedway where they get in the way of the next round.

Loose key on top of the bolt carrier:  Should be torqued down to 50’ lbs. with Loctite.

Blown primers:  Shooting 5.56 our of .223.

Headspace: Reloads break after two or three loads because of too much headspace. Too little headspace mimics the problem of too little gas which is short stroke.

Failure to eject:  Usually caused by combination of small faults, such as brass filings building up under ejector due to sharp edges on soft cases.


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Magazines: Thread on Good Deals on Magazines


Good Gear:



Stay away from: any aluminum magazine without a manufacture’s stamp on the baseplate, any “used” G.I. magazines, and any polymer magazines other than Magpul brand.


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Aluminum “G.I.” Magazines:


Aluminum magazines for AR/ M-16 rifles, when manufactured under heavy quality control, are very reliable. Their weakness, however, is that their thin and delicate bodies and feed-lips can be easily damage if dropped or landed on.

Aluminum AR magazines are made in either 20 or 30-round capacity. There are a few low-grade manufacturers that have made 40-round magazines throughout history. Avoid these. Traditionally as a general rule, the lower round capacity of a magazine, the more reliability you can expect. The 20-rounders were considered the most reliable, and for a little less reliability you could get 30-round magazines. With increases in manufacturing technology and experience the 30-round magazines can be expected to be just as reliable as the 20-round magazines. Still, avoid the cheap 40-round magazines.

Aluminum magazines have been manufactured by numerous manufacturers over the years. They are not all equal in quality of the stampings and welding tolerances.

The manufacturer’s logo will be stamped or engraved into the bottom of the floor-plate of the magazine (shown left).  Avoid magazines that do not have any type of manufacturer’s mark on the floor-plate. There is no way of telling who made them or how reliable they are.

Stay away from unbelievable deals on used G.I. aluminum magazines at gun-shows and internet listings. In the military “used” translates to “abused”. There is a very good chance that the magazine lips may be bent out of spec, or the spring may be worn out. New quality magazines are now too plentiful and inexpensive for you to take the chance with acquiring junk.


D&H  Brand Magazines:

D&H brand magazines are considered top-of-the-line.  They are made on former Labelle tooling.  They are OEM for several AR-15 manufacturers.


Brownell’s Magazines:

Brownell’s brand magazines are considered top-of-the-line.  They are approved for military use.


Surefire Brand Magazines:

Surefire MagazineSurefire (the company that builds tier-one weapons lighting systems and weapon sound-suppression systems) recently started selling 60 and 100-round aluminum magazines. The idea is that you can keep shooting your way out of trouble, rather than get shot while reloading. This is a great idea, but the downside is that they hang a long way under the rifle which can restrict movement and the ability to shoot from prone or unorthodox positions. They are supposed to be ultra-reliable, but they are very expensive. It is too early (as of Q3-11) to tell if these are as good as advertised. Like any quality, super high-capacity magazine, you have to make a cost/benefit analysis on whether the additional firepower capability is worth the additional expense (you can buy 10 high-quality 30-round aluminum magazines and carry 300 rounds of ammunition for the same prices as carrying 60 rounds of ammunition in one Surefire magazine). Also, if the single magazine of 60 or 100 rounds of ammunition is damaged (dropped or shot), then you are out that many rounds of firepower. If the same damage occurs to a less expensive 30-rounder, dump the magazine, load a fresh one, and get back into the fight. A final note: the 60 and 100 round magazines are very long compared to a 20-round or 30-round magazine. They will hang out of the bottom of the rifle considerably farther than lesser capacity magazines. This will greatly hinder your ability to fire from the prone position.


Colt, H&K, and C-Products Brand Magazines:

Coming soon!


How To Disassemble a “G.I.” Aluminum Magazine:

How To Disassymble a US GI Magazine


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Polymer Magazines:


The AR-15/M-16 rifle system was originally designed to use magazines manufactured from lightweight, thin aluminum. It was problematic to design a polymer AR magazine thin enough to hold a high volume of rounds, fit into the rifle, and still maintaining strength, integrity, and heat resistance of the magazine body and feed-lips. The magazine would need to hold together under fully loaded spring pressure, and then not melt when fired from hot, automatic weapon. Eventually advances in polymer manufacturing technology allowed the creation of plastic magazines thin enough and strong enough to be used AR/M-16 weapon systems.


Magpul P-Mag Magazines:

How to disassemble and reassemble the P-Mag

Magpul Industries P-Mags are considered absolute tier-one equipment. They are manufactured in both 20-round and 30-round capacity versions, and come in black, olive drab, and tan. There is a version that sports a thin, clear window on the side so the operator can view how many rounds are left in the magazine. When you purchase them, verify that you are getting the “M revision” version. With this design update the part of the magazine that inserts into the weapon’s magazine well has been modified. There were issues with their fit and function when used in some non-AR rifles which are designed to accept NATO M-16 (AR) magazines. Unless you think that you will ever use the magazines in a non-AR style rifle you probably shouldn’t really worry about it. Fortunately, the “M” revision has been out a while and I haven’t seen anyone selling the pre “M” version for quite some time, so you probably will not have to worry about it. Magpul now has a “Gen-3” version out. There are some a few ergonomic improvements, but functionally they should be the same as the “M” revision.


Thermold Magazines:

Manufactured by Master Molder, Thermold magazines were used by the Canadian military for a brief time, and the company liked to brag about it. Eventually they were taken out of service and replaced with traditional aluminum magazines. They are fairly reliable, but the Canadian military discovered that the feed lips on the magazines were prone to melt when used in weapons on full-auto. As a civilian with a semi-automatic weapon, you will probably not ever get a Thermold hot enough to melt the magazines, but with other similarly priced polymer magazines on the market that are more heat tolerant, I would stray away from them and go with either high-quality traditional aluminum magazines, or Magpul Industries polymer P-Mags.


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Super High-Capacity Drum Magazines:


Beta Drum Magazine:

C-Mag “Beta” Magazine is a 100-round dual drum magazine designed to provide the operator with sustained firepower. It was used extensively in the early years of the post 9/11 war on terror by our military and private contractors. While exponentially higher quality than the MWG snail magazine (seen below), they are complex mechanisms, require careful maintenance and graphite lubrication, and over time have proven prone to malfunction or breakage during the stress and abuse of combat. Serious operators have begun to stray away from these. Beta magazines are also very expensive. For the Beta’s retail price of around $225 you could instead purchase more than 20 30-round high quality aluminum G.I. style magazines, and have the capability to load six times as much ammunition as the Beta.


MWG Snail Magazine:

This plastic 90-round magazine has been around since the days of Miami Vice. It is more of a novelty item than a piece of serious equipment. Its plastic is less than top quality. It has a marginal reputation for reliability. When loaded into the rifle it adds the combined weight of the magazine plus 90-rounds of ammunition way out to the left side of the rifle, thus creating an asymmetric balance and a decrease to the rifle’s handling characteristics.  They suck.


To the right we can see Miami Vice’s Crocket and Tubbs about to blast a fool who was dumb enough to invest his hard-earned money on a MGW snail mag.


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Backup Iron Sight (BUIS):




Coming soon!



To Co-Witness or Not:’s Guide To Understanding Co-Witness



What Are Good Brands?

Coming soon.


BUIS on Bushmaster Brand Rifles With Removable Carry Handle:

Colt A3 Removable Carry Handle Sights are taller than A1& A2 Rear Sights, and require an .040” taller Front Sight Post.

Colt Front Sight Post vs. Bushmaster Front Sitght Post

More soon!


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What Distance to Zero Your Red Dot Sights and Backup Iron Sights:


It is important to zero the elevation of the sights with a single setting that will take the most advantage of the flat shooting trajectory of the 5.56mm/.223 caliber rifle round.  The following diagram compares the trajectories of bullets when zeroed at 25, 50, and 100 yards.  It is easy to see why the 50 yard zero is the best choice, and how your point-of-impact will never be more than +/- 2.5 inches from your point-of-aim, from close up and personal “bad breath” distance, all the way out to a distance 225 yards.

5.56mm / .223 caliber zero comparison

25, 50, & 100 Yard Zero Comparison

100 Yard Zero

100 Yard Zero

300 Meter Zero

300 Meter Zero

Improved Battle Sight Zero

Improved Battle Sight Zero


Battlesight Zero For Red-Dot Optics:

Simply zero your rifle for point of sight / point of impact at 50 yards.  Make adjustments until bullet impact is right on the red dot.  For shots at 300 meters simply hold over approximately one dot.


Battlesight Zero For BUIS Without Elevation Adjustment:

With the majority of BUIS you can not adjust the elevation of the rear sight.  If you have a red-dot optic installed, first sight in the optic as precisely as you can at 50 yards.  Then use a front sight post adjustment tool to raise or lower the front sight until the it appears that when you are looking through the front and rear BUIS and the optic that the red dot is horizontally intersected by the tip of the front sight post.  If you do not have an optic installed, simply adjust your point of impact by adjusting the front sight for point of sight / point of impact at 50 yards.




Improved Battlesight Zero For Carry Handles With Adjustable Rear Sights:

The standard A2 rear sights on an AR-15/M16A2 were designed with elevation settings for 300 to 800 meters. The Santose Improved Battlesight Zero allows for an elevation setting of 50 yards / 200 meters for one of the most all-around useful trajectories obtainable with the 5.56mm/223 Remington cartridge when fired from an AR-15. Neither of the above sighting schemes allow for an elevation setting giving you point of aim equals point of impact at 100 yards.  Since 100 yard shooting ranges are some of the most commonly found ranges in the United States, it would be useful to have such a setting on our AR-15s. This can be achieved quite easily with nothing more than a 1/16” allen wrench. It’s really just a matter of taking the Improved Battlesight Zero one step further.  See this link to learn how to do this:’s Revised Improved Battlesight Zero



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AR-15 Links:


Link to Firearm Refinishing and Camo Picture Thread

Link to Pinestraw Camo Picture and Tutorial Thread


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Optics: Scopes and Red-Dots:

Savannah Arsenal’s Defensive Rifle Optics


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Shooting with Iron Sights:


Proper AR-15 Eye PlacementWhen shooting with magnified optics, red-dot or holographic optics, or iron sights, for proper eye relief you should have your face far enough forward on the fixed stock or retractable stock tube so that your nose is almost touching the charging handle.


AR15A2_toobig_3458In the photo to the right the shooter has their eye excessively far back from the rear sight.  This is a telltale an inexperienced shooter.


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  • Buy a quality AR-15 / M-4 appropriate for your perceived needs.
  • Purchase at least 10 quality aluminum or polymer 30-round magazines.
  • Equip the rifle with an Eotech or Aimpoint red-dot optic (magnified optics if you live in a rural area).
  • Install a quality backup iron sight.
  • Zero optics and iron sights at 50 yards.
  • Equip the rifle with a quality lighting system.
  • Keep the weapon cleaned and properly lubricated.
  • Make sure that optics and other accessories are properly installed with Loctite.
  • Keep spare batteries for optics and lights.
  • Get formal training, and Practice, Practice, Practice.


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One comment on “AR-15 / M-4

  1. Just placed the “Mako” mag well grip on my Ar. Fits tight with no problem in magazine exchanges. Added next to no weight. I recommend at least looking at one near you.

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