AR15 / M4


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

– Colonel Hal Moore, United States Army –


Introduction to the AR15:


The Developmental History of the AR15 and the M16 / M4:

In the beginning there was the M16 (pictured right). It featured a fixed carry handle with a rear sight that was only adjustable for windage.  The front sight was used to adjust elevation. The hand guards were triangular shaped.  The grip had no index finger groove. There wasn’t a brass deflector or no forward assist. The thin, non-chromed, 1:12 twist barrel sported a three pronged flash suppressor.  The rifle could fire in both semi-automatic and full auto.  At some time in the early years the barrels became chrome lined.

The M16A1 added a forward assist.  Some A1s sported a birdcage flash suppressor.

M16A1 Rear SightFor civilian legal AR15 rifles, the “A1” designated a model with a fixed carry handle with only windage sight adjustment (seen right). Some were slick sided like the early M16 rifles. Some feature forward assists like the M16A1.

The M16A2 added the brass deflector.  The fixed carry handle rear sight was improved and was adjustable for both windage and elevation. The barrel’s twist was made a faster 1:7 twist to stabilize heavier tracer rounds.  Its profile remained thin in under the hand guards to facilitate the M203 grenade launcher, but was made heavier ahead of the front sight base and the barrel .  Flash hider was a modified birdcage with an enclosed bottom to prevent dust from being kicked up while firing prone.  Hand guards were changed from triangle to round.  The pistol grip had an index finger groove.  The butt stock was lengthened and strengthened.  The full-auto mode was replaced with a three round burst mode.

The AR15A2 often feature barrels with either 1:7 or 1:9 twist rates, and heavy profiles under the hand guards.

M4 CarbineThe M4 carbine (pictured right) was originally developed for special operation and airborne troops.  It has since become general issue. It featured a flat-top upper receiver with removable carry handle and similar adjustable rear sights to the A2, but with less elevation adjustment.  The 14.5″ barrel has cutouts to accommodate the M203 grenade launcher.  The flash hider and rifling twist rates are the same as the A2. The front sight base height was changed to correct sight alignment with the carry handle and for the shorter sight radius of the carbine.  The feed ramps were enlarged on the barrel extension and extended into the upper receiver itself to improve reliable feeding during automatic or burst fire. Larger diameter carbine hand guards with double heat shields were added.  The butt stock is collapsible.  Early versions used three round burst and current production are full auto.

m4 16 inch barrel bayonet problemCivilian M4 barrels may have a 1:7, 1:8, or 1:9 twist rate.  Most barrels are 16″ with a removable flash hider to meet BATE regulations.  Because of the increase in barrel length, a Mil-Spec bayonet can not be properly fitted onto the rifle (pictured right).  Some have 14.5″ barrels with a 1.5″ flash hider or recoil compensator permanently attached to meet the BATFE regulations.  The civilian versions should still feature M4 feed ramps, dual heat-shields in the hand-guards, and grenade launcher cut-outs under the hand guard.

A3 and A4 rifles have 20″ barrels.  The A3 is basically an A2 that has replaced the burst feature in favor of a return to full auto. Like the M4, the M16A4 is a flat-top upper with detachable carry handle and may feature three round burst or full-automatic fire.

Civilian AR15 clones of the M16A3 and M16A4 rifles my use either the A3 or A4 designation to describe 20″ flat-top rifles.  Many commercial clones differ from mil-spec M16 rifles in that most feature 4140 chrome-moly steel instead of the military grade 4150. Many companies do not make chrome lining standard.  Rifling twists are more commonly 1:9 twist, and barrel profiles are often different than military rifles made to mount grenade launchers.

m16 mk12 mod 0Other variations that are not general issue in the military are Special Purpose Rifles (SPR).  These were originally developed as special purpose uppers to give Special Operations troops the capability to provide precision fire in a compact package. Features include a free-floated, match grade, 18.5″ barrel mounted to a flat-top receiver. Purpose built uppers have now evolved into Special Purpose Rifles instead of uppers only.  Variations include the Mk12 mod-0 (seen right),  and the Mk12-mod-1.

SDMRThe SDMR (pictured right) and SAM-R rifles are the Marine Corp’s and Army’s squad level marksmen rifles intended to add precision capability to the squad level of all units. These rifles feature match grade, 20″ stainless steel free-floated barrels, equipped with magnified optics (ACOG or Leupold).


National Match service rifles used by military marksmanship teams for competition must retain outward appearance of the A2 or A1 rifles but are enhanced to increase the competitive edge within the rules. They often feature match grade barrels with fast twist rates to accommodate heavy bullets with long profiles to reach out to 1000 yards. The barrels are free-floated in tubes that accommodate the standard hand-guards. Match triggers are used but can not be lighter than 4.5 lbs.  Finer profile sights with finer adjustments are used.  Flash hiders and bayonet lugs are optional to accommodate shooters who live in states that still retain bans on these features.


Related Website, Blogs, and Articles:

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How the AR15 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:



Decision Making Factors on Which System To Choose:



Coming soon.

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 “Say hello to my little friend!”

– Tony Montana, From the Motion Picture Scarface –

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 AR15 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.


What is Mil-Spec?

Most AR15 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.


Tier One AR-15 Rifles:

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


Tier Two AR15 Rifles:

Excellent quality, but without the price of the Tier One rifles. Perfectly suitable for prepper duty.

  • Bushmaster: Rifles manufactured before Remington bought the company.)
  • 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 where M-4 rifles are manufactured under contract for the US military.  I can not say with 100% certainty if the parts are the exact same as what goes on the mil-spec military rifles.  Since I don’t know enough about the origin, manufacturing process, or final assembly, I can’t place them in the coveted Tier One category, but I have only heard good things about these rifles.
  • Ruger AR-556: I haven’t heard anything bad about these rifles, but I haven’t heard anything good either, unless it was from a review in a magazine that also advertised for Ruger.  They company has always made solid products, so I can’t help but believe that their rifles should be solid.  If you have a choice between the direct-impingement model or the gas-pistol model, go with direct-impingement (DI).
  • Stag Arms


Tier Three AR-15 Rifles:

Entry level.  An economical way to start learning the AR15. They may or may not be survive the torture received in serious carbine type training classes and extended self-defense scenarios.


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. They are shit.  Do not buy one.
  • 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 AR15?


The Difference Between .223 Remington and 5.56mm NATO:

  • .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 NATO 55-grain ball cartridge.
  • M196:  5.56×45mm NATO 54-grain tracer cartridge, red cartridge tip.
  • M855:  5.56×45mm NATO 62-grain FN SS109 ball cartridge, green tip w/steel penetrator and a lead core.
  • M856:  5.56×45mm NATO 64-grain FN L110 tracer cartridge.
  • M262:  5.56×45mm NATO 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 AR15 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 AR15.



  • 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 to 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 AR15 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 M16 / AR15 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:

AR15 Parts Diagram:

M4 Parts


AR15 Lower Parts:

AR15 Lower Receiver Parts


AR15 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 AR15 Hacks: Destroying 4 AR Maintenance Myths


How To Fieldstrip the AR15:’s How To Field Strip the AR15


How to Clean and Lube the AR15:

  • 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 AR15:


AR15 / M4 / M16 Operating Manuals in PDF:

Armalite-AR10-M15 Manual PDF

Bushmaster Manual PDF

US Army M16 Manual PDF

US Army M16 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 / M16 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 stamping 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 AR15 manufacturers.


Brownell’s Brand Magazines:

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


Surefire Brand Magazines:

Surefire (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 AR15 / M16 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 /M16 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 STANAG M16 (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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Sighting Options – Backup Sights & Optics:

Fixed Carry Handle Sights:

Early AR15 style rifles had a fixed carry handle with an integral rear sight.  If your carry handle is removable, then skip down to Removable Carry Handle.

You may choose to leave your rifle stock and simply use the sights that came on the rifle and not add any optics.  If that is the case, it is recommended that you simply adjust your sights so that your point-of-aim (POA) and the rifle’s point-of-impact (POI) are the same at 50 yards (meaning that the rifle hits where you are aiming at 50 yards).  This will give you a very flat trajectory out past 225 yards.  The benefits of a 50 yard zero are discussed farther down this page with What Distance to Zero Your Red Dot Sights and Backup Iron Sights. Should you wish to adjust your sights so that you can have a specific setting for 50 yards and 100 yards, and still use the 300 – 800 meter settings, read about the Improved Battle Sight Zero farther down this page.

You may wish to add some type of optic, but with fixed carry handles there aren’t many truly useful options.

ar-15 with scope mounted high on fixed carry handleThere are several options for mounting optics on top of the carry handle, but this method set the optic so high that the shooter can’t get a good cheek weld on the stock. With the optic mounted excessively high (as seen in the photo to the right) there isn’t any distance to zero the rifle that won’t destroy the fantastic flat trajectory of the .223 Remington / 5.56mm NATO cartridge that results when optics are normally mounted with the dot, reticle, or crosshairs 2.5″ above the center of the rifle’s bore like the iron sights are.

ar-15 fixed carry handle forward optic mountAnother option is to add a mount to the carry handle that carries holographic or red dot optic forward of the carry handle over the forend.  It can hold an Eotech or Aimpoint optic so that the reticle is co-witnessed with the iron sights of the rifle.  Note that you can’t mount a magnified scope forward of the charging handle as you would never be able to get proper eye relief on the optic.

Fixed Carry Handle ACOGSome models of Trijicon’s ACOG magnified optics are designed to mount in the channel of the carry handle.  There is a small hole through the mount so that you can still use the iron sights on the rifle should the ACOG be put out of commission.  This may be your best way to mount a magnified optic to the top of the carry handle as low as possible.  You still won’t have the optimum cheek weld or ballistics, but you can make it work.

AR-15 Cheek RiserIf you mount an optic to the top of the carry handle then you might want to think about adding a cheek riser to your stock (as seen in the photo to the right).  This will allow you to properly position your head behind the optic.  There are cheek rests for both fixed and telescoping stocks.  Research carefully before purchasing your cheek riser as some may block the operation of the charging handle unless the stock is fully extended.  If you mount a holographic or red dot optic forward of the carry handle then you won’t need a cheek riser.


Flat-Top Rifle With Removable Carry Handle Sights:

As discussed above, if you have an older AR15 it may have a fixed (non-removable) carry handle that is part of the forged upper receiver.  If this is the case, your rear sight is built into the carry handle and this section does not pertain to you.

AR-15 M-4 Flat TopMost AR15 style rifles built in the past ten to fifteen years do not have a built in carry handle / rear sight assembly, but rather a “Picatinny rail” that allows the user to have a choice as to mount holographic sights, red-dot sights, magnified optics, simple rear sights, or even a removable carry handle / rear sight assembly.  These are referred to as “flat top” rifles (pictured right).  In the past, anyone wanting to mount optics on top of their AR-15 style rifles were forced to use some type of adaptor to mount their optics on top of the fixed carry handle.  This set the optics too high to take advantage of the 5.56x45mm NATO rounds fairly flat trajectory, and it set the optic too high for the shooter to get a good cheek weld on the stock.  The flat-top design allows you to mount your optics so that the aiming reticle is the same height above bore as the tradition fixed “iron sights”.

AR-15 Removeable Carry HandleSome flat top rifles are sold with a removable carry handle that looks exactly like the older fixed carry handles, except that they can be easily removed with two knobs.  Some rifles are sold without the carry handle as manufactures realize that most end users will want to remove them to customize their rifles with optics and accessories.  If you choose to simply use the carry handle then don’t mount any optics to the top of it.  This defeats the purpose of the removable carry handle.  Remove it and mount the optics to the rifle’s rail.


Red-Dot Sights, Holographic Sights, and Magnified Optics:

Savannah Arsenal’s Tactical Rifle Optics Page

As noted on the page linked above, shooting from CQB distances out to 200 meters can greatly be aided with the use of red-dot or holographic optics.  They are much easier to shoot with than traditional iron sights.  Examples are discussed on that page.

Magnified optics on tactical rifles are beneficial when shooting past 200 meters.  While some magnification can help you identify and prosecute threats at intermediate distances, too much magnification can limit your peripheral vision and affect your ability to detect threats. It is recommended to limit the magnification power of optics intended for tactical / fighting rifles to 4x.  Examples of magnified optics are also discussed on that page.

Always keep spare batteries for the optic with the rifle.  I really like Magpul’s MOE grips (pictured right) as they have a compartment where you can store spare batteries for your optic or weapons light.  I place the battery in a small plastic arts & crafts “crack bag” before storing it in the grip.  (If you replace your grips, be very careful as there is a very small spring and pin that may fall out when you remove the original grip.  Be careful not to damage the spring when installing the new grip.  Be sure to add a dot of Loctite to the screw that holds the grip to the rifle’s receiver.)

Be sure to add a Backup Iron Sight (discussed next) as batteries can go dead and electronics can fail or be destroyed.  With backup sights you will be able to stay in the fight.


Backup Iron Sights (BUIS):

xW7465_SI_WilsonCombatTacticalCustom522_0279BUIS is an acronym for “backup iron sights”.  This is nothing more than a catchy label for backup sights that you can use when and if your primary electronic or magnified optic is damaged or fails.  “Iron” simply refers to their metal parts to differentiate them from electronic optics, although none of them are made from iron, but rather aluminum, steel, and plastic.  Backup sights can simply be a rear sight that sits on a flat-top receiver behind the optic, or it may be a  set of both front and rear sights for an ORC (Optic Ready Carbine: a carbine with only rails on top and no front sight base that is ready for customization by the end user).

If you run some type of aiming device (holographic sight, red-dot sight, or magnified optic) on your rifle then you need to have a backup sight(s) on your rifle.  Murphy’s Law dictates that your electronic optics will break or be damage, your scopes will break or fog up, and your batteries will go dead at the worst time.  If this happens and you don’t have a backup system for aiming, then that weapon is out of the fight.  You soon will be too.

One day, after making a long drive to the range to shoot my M4, I discovered that my Eotech’s batteries were dead.  Although I was ashamed for not having an extra set of batteries with my rifle or in my range bag, I was still able to utilize the rifle’s backup sights and enjoy a long morning of shooting.  Now, besides installing backup sights on all of my rifles, I store an extra set of batteries in each rifle’s Magpul MOE aftermarket pistol grips, and keep extra batteries in my range bag.

Stay away from cheap Chinese made “Airsoft” quality parts and gear, such as Aim Sports, Promag, Leepers, UTG or NcStar. Save your money and buy quality gear. Your life may depend on it. As always, when you install any parts, be sure to use Loctite thread locker on the threads of the screws to keep your parts from loosening up when you shoot.

Manufactures of Quality Backup Sights include:

If you are going to install backup sights on a Bushmaster carbine, be sure to read:
Backup Sights on Bushmaster Brand Carbine With Removable Carry Handle

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What Distance to Zero Magnified Optics:

Magnified Optics with Bullet Drop Compensation (BDC):

ACOG Bullet Drop Compensator (BDC) and Ranging CapabilityIf you are using a magnified optic that has bullet drop compensation (BDC) stadia markings for .223 Remington / 5.56mm NATO ammunition then you should zero the rifle so that bullet impact is appropriate for corresponding distance’s marking in the optic (at 100 meters the bullet’s point-of-impact hit where you aim with the 100 meter stadia marking).  The rifle should then hit point-of-aim at 200 meters when aiming with the 200 meter stadia marking, 300 meters with the 300 marking, etc.


Magnified Optics with Non-Specific Stadia Markings:

mil-dotIf you have a magnified optic with non-specific markings, such as mil-dot, you may choose to zero the rifle at 50 yards.  With a 50 yard zero you know that your rounds will hit within a 2.5″ circle from 10 yards out to approximately 250 yards (discussed further down).  For shooting greater than that distance you will have to shoot at known distances and and experiment to figure out how much hold-over you need for a given distance (shoot, observe where the round hit, and keep adjusting until you know how many dots to hold-over for that particular distance.  Record the rifle’s “dope” on a card or piece of paper that will stay with the rifle.  You will forget the information and will be glad that you kept the information.


Magnified Optics with Simple Crosshairs or Reticle:

Simply zero the rifle at 50 yards.  You will hit withing a 2″ circle from 10 yards out past 225 yards without any holdover. (Explanation below)

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What Distance to Zero Non-Magnified Optics & Sights:

Battle Sight Zero:

Simply defined, “Battle Sight Zero” is a theoretical “set it and forget it” setting for your iron sights or non-magnified optics.  You will want your sights set at a distance that will provide the flattest trajectory, and thus the least deviation in point-of-aim and point-of-impact at varying distances.  Fortunately for those using .223 Remington / 5.56mm NATO rifles, there is a distance that you can zero your rifle and enjoy a very flat trajectory out past 200 yards away.


Find The Flattest Trajectory:

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.


100 Yard Trajectory:

100 Yard ZeroThe first chart shows the trajectory of a 5.56mm NATO round when fired from an AR15 style rifle.  The dash line represents the shooters point of aim.  The bullet departs the barrel approximately 2.5″ below the point of aim.  It’s flight path reaches the shooters aiming point at 100 yards (point-of-aim (POA) = point-of-impact (POI).  The bullet then drops back down to 2.5″ below POA at 200 yards, and plummets drastically after that.  This isn’t a terrible zero if you never plan on shooting past 200 yards as the bullet will impact somewhere within the distance of the barrel to the top of the rifle’s sight base.  Not terrible, but you can do better.


25 / 300 Meter Trajectory:

300 Meter ZeroThe next graph represents the traditional military method of zeroing the rifle at 25 / 300 meters (meaning that you zero the rifle at 25 meters and can expect POA = POI at 300 meters).  This was traditionally done with adjustable rear sights, such as those found on rifle’s equipped with carry handles, set on the 300 meter setting, but the target set 25 meters away.  This is a TERRIBLE zero setting.  At 100 meters (91 yards) the your rounds will impact over 4″ above your POA.  At 175 meters the bullet impact will reach its peak apogy at roughly 6″ above your POA.  The USMC has finally accepted that this isn’t the most efficient way to zero an AR15 / M16 style rifle.  Do not use a 25 meter “set it and forget it” zero.


50 Yard Zero:

The next graph illustrates the ballistic trajectory of a 5.56mm NATO round with a 50 yard zero.  This zero is commonly referred to as “Improved Battle Sight Zero”.  As with the graphs above, you can see that the bullet leaves the rifle 2.5″ below the point-of-aim (POA).  The bullets trajectory will pass through the shooters point-of-aim at 50 yards.  At 100 yards it impact approximately 1.5″ high.  It will reach its peak apogy of 1.8″ at approximately 140 yards.   Around 220 yards the round will again pass through the shooters (POA).  At 250 yards the round will impact approximately 2.5″ below POA.  This data shows that on its flight from the rifle’s muzzle out to 250 yards, the bullet will hit somewhere within plus or minus the height of the rifles front sight base (+/- 2.5″).  That’s pretty darn flat.


50 Yard, 25 / 300 Meters / 100 Yards Trajectory Comparison:

5.56mm / .223 caliber zero comparisonThe final graph compares all three trajectories.  The 100 yard zero isn’t terrible, but you can do better.  The 25 / 300 meter zero is terrible.  The 50 yard zero will provide the combat shooter with the flattest trajectory out to approximately 250 yards, and is the recommended distance to zero your iron sights and non-magnified optics as a “set it and forget it” Battle Sight Zero setting.


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Battle Sight Zero For Red-Dot and Holographic 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.

co-witnessAs discussed earlier, if you are going to install any type of electronic aiming device, it would be prudent to install some type of backup sights.  You will also want the backup sights to be zeroed at 50 yards.  With the optic and the backup sights properly installed and zeroed, it will look like the aiming dot of the optic is bisected by the top of the front sight post.  The sights and optic will then be considered “co-witnessed”.


Co-Witness Iron Sights and Optics:’s Guide To Understanding Co-Witness

Eotech CowittnessThe easiest way to co-witness your optic and backup sights will be to carefully zero your optic first on the range so that your bullets are hitting exactly where you aim at 50 yards.  You want to zero your optic first because it can be more finely adjusted than most backup sights.  Next you will zero your backup sights. If your optic is correctly zeroed then you won’t have to fire a single shot to zero your backup sights. With the majority of backup sight you can not adjust the elevation of the rear sight. You must use a front sight post adjustment tool to raise or lower the front sight until it appears, when you are looking through the front and rear backup sight, that the optic’s reticlet is horizontally bisected by the tip of the front sight post.

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Zero For Carry Handle Sights:

Improved Battle Sight Zero For Carry Handles With Adjustable Sights:

The standard A2 rear sights on an AR15 / M16A2 were designed with elevation settings for 300 to 800 meters. The Santose Improved Battle Sight 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 Battle Sight Zero one step further.  See this link to learn how to do this:’s Revised Improved Battle Sight Zero

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Proper Cheek Weld and Eye Relief:

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 of an inexperienced shooter.

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.22LR Conversion Kits:

AR-15 Conversion Kit
Savannah Arsenal’s CMMG Brand Conversion Kits For AR-15 Rifles

Savannah Arsenal’s What Distance To Zero Your .22LR Conversion Kit Equipped AR-15 or Dedicated .22LR AR15

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  • Buy a quality AR15 / M4 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 “AR15 / M4

  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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