AR15 / M4 / M16

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

– Colonel Hal Moore, United States Army –


AR-15 Essentials:

Ammunition For The AR-15:

AR-15 Maintenance & Repairs:

AR-15 Magazines:

AR-15 Sights and Optics Mounting Options For Fixed Carry Handle Rifles:

AR-15 Sights and Optics Mounting Options For Flat-Top Rifles:

AR-15 Optics:

Weapons Manipulation:


Final Recommendations:


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 from 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.

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How the AR15 Works:

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Direct Impingement vs. Gas Piston:


Direct Impingement:

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.

Direct impingement style AR / M-16 style rifles have been in use by the military and civilians for over 50 years and have sent a lot of bad guys to meet their makers.  Because the bled off gas that cycles the action vents into the upper receiver, some suggest that the direct impingement rifles will run hotter, and gunshot residue in the gas will dirty the action and affect reliability.  I have never heard of a properly maintained direct impingement style AR failing because of this system.  With quality ammunition and appropriate lubrication application you can expect a direct impingement AR style rifle to run reliably for hundreds, if not thousands of rounds.  In a carbine class where the gun was run fast and hot I have fired 1300 rounds through a S&W M&P carbine without a malfunction.

Direct impingement systems are traditionally quieter when operating with a suppressor.  That being said, you may experience more gas blow-back in your face and gunshot residue in upper receiver as well as down in your magazine when shooting a direct impingement AR style rifle with a suppressor.  When operating with a suppressor, wear protective glasses, and be sure that the rifle is properly lubricated.  Grease works great because it won’t be blown back in your face like oil.


Gas Piston:

Gas pistol style rifles do not vent dirty gas into the receiver, but rather through vents located under the handguards.  This may help to keep the rifle from running as hot as a direct impingement style rifle during sustained fire.  Also, the rifle may go longer before becoming noticeably dirty inside.

Generally speaking, gas piston rifles can not be quieted as much as a direct impingement style rifle when using a suppressor.  Some people purchase gas pistol style rifles thinking that they won’t get gas blowback in their face when using a suppressor, but you are just as likely to get it from a piston rifle as you are a direct impingement rifle.

Generally speaking, gas piston style AR rifles are not as accurate as direct impingement style AR rifles.  If you are shooting a “fighting” style rifle you probably will not be able to tell any difference between a gas piston and a direct impingement style rifle, however you won’t find any “precision” gas piston style AR rifles on the market.

There is not such a thing as a “Mil-Spec” gas piston AR style rifle.  Each manufacturer will have their own proprietary system that don’t share common parts.  From a prepper’s perspective, if you buy gas piston rifle(s), it is recommended that you buy and store any spare parts that could ever possibly fail on your rifle.  Direct impingement style AR rifles are in abundance, and most parts are interchangeable.  Parts on your gas piston style AR are not, and your rifle will be almost impossible to repair after the SHTF.



Decision Making Factors on Which System To Choose:



Direct impingement style rifles have been reliably putting down bad guys for over half of a century.  Spare parts are easy to find during the good times, and parts are easily cannibalized from other direct impingement style AR rifles after the SHTF.  Stick with the tried and true, military style direct impingement style AR rifle.  If you insist on owning piston style AR rifles, make sure to purchase spare parts now why you can.

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Tiers of Quality:

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:



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:



  • 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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AR15 / M4 / M16 Operating Manuals in PDF:

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AR-15 Parts:

AR15 Parts Diagram:


AR15 Lower Receiver Parts:

AR15 Lower Receiver Parts


AR15 Bolt Carrier Group (BCG):

AR15 Bolt Carrier Group 1


Types of Bolt Carriers:

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Fieldstripping, Cleaning, and Lubrication:

Cleaning & Maintenance:


How To Fieldstrip 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.
  • Lubricate moving parts. Use high-temperature wheel bearing grease. Do not use Lithium grease. See video below.
  • 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.

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AR-15 Malfunctions:

Five Most Common AR-15 Problems:

  1. 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.
  2. Loose key on top of the bolt carrier:  Should be torqued down to 50’ lbs. with Loctite.
  3. Blown primers:  Shooting 5.56 our of .223.
  4. 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.
  5. 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.


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

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AR-15 Magazines:

AR-15 Magazine Selection Criteria:

These are the suggested criteria in the order of importance that you should take into consideration when choosing magazines for your rifle:

  1. Reliability
  2. Capacity
  3. Material (aluminum, steel, polymer, plastic)

For a thorough AR-15 magazine review and buyer’s guide, be sure to check out:


Magazine Capacity:

5-Round Box Magazine: Typically used for hunting where local regulations limit the number of rounds in the hunting firearm to 5-rounds, or in some competitive target shooting. Useless for self-defense.

10-Round Box Magazine: Typically used in backward-ass states that limit firearm magazine capacity to 10 rounds, or in some competitive target shooting.

20-Round Box Magazine: Perfect for shooting from a prone position or from a tabletop at the range. It is a good idea to have one or two of these in your inventory to use when you zero an AR-15 so that you can rest the forend of the rifle on a beanbag or bipod and not have the magazine touch the shooting table.

30-Round Box Magazine: 30-rounds are the most common AR-15 magazine capacity. They present a good balance of reliability, capacity, mobility, and shootability.

40-Round Box Magazine: Traditionally as magazine capacity increased, their reliability decreased. In the early days of the M-16/AR-15 the 20-round magazines were the most reliable, followed closely by 30-round magazines. I am not aware of a 40-round magazine having ever been issued by the military, and most commercially available 40-rounders available to the public were very unreliable.

Magpul and several other companies have recently released 40-round polymer magazines. Magpul’s 40-round P-Mag has earned a reputation as being very reliable. Two reasons that might give you pause about 40-round magazines is that it is hard to find magazine pouches made them, and it is more problematic to shoot from a prone position or rifle range tabletop with a tall magazine.

60, 75, & 100-Round Drums: x


Aluminum Box 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.

AR15 magazine baseplate d&HAluminum 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.

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

How To Disassymble a US GI Magazine


Polymer Box 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.


Drum Magazines:

I am not a big fan of drum magazines. They are heavy and awkward. Most are very unreliable as they have delicate and complicated mechanisms that are prone to jam up. They are all expensive. You can typically purchase 10 to 15 quality 30-round stick magazines for the price of one drum.


 AR-15 Magazine Recommendations:

Qualtity Gear:


  • Any aluminum magazine without a manufacture’s stamp on the baseplate.
  • Any “used” G.I. magazines.
  • Promag.
  • National Magazine

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Introduction To Sights and Optics For AR-15 Rifles:

Older AR-15 Rifles With Fixed Carry Handle:

Fixed Carry Handle Sights:

If you have an older rifle with a fixed (non-removable) carry handle then you can make adjustments to the rear sight that will allow you to have settings for a 25 yard, 50 yard, and 100 yard zero.  You will also still be able to use the 300 to 800 meter settings.  To learn several different methods to zero the sights on a fixed carry handle rifle, including the method use by the US Army, as well as the method used by the US Marine Corps, check out:

Fixed Carry Handle Optics Options:

With a rifle with a fixed carry handle you will be limited with your choices of how to mount optics.  Optic mounting options are discussed at:


Flat-Top AR-15 Rifles — Removable Carry Handles:

AR-15 Removeable Carry HandleThere are removable carry handles that fit on flat-top rifles.  It is possible to mount optics on top of the carry handle, but this is inefficient and mounts the reticle or crosshairs of the optic higher than the optimal 2.5 inches above the bore (the height of the front sight and the rear carry handle sight).  If you want to mount optics on the rifle, remove the carry handle and mount them directly to the rifle.  If you want to use the A2 style sights then check out:



Flat-Top Rifles With Backup “Iron” Sights (BUIS):

Troy-BattleSight-Front-HK-Folding-2Backup sights are intended to be used should the primary optic fail (break or dead battery).  Most rear backup sights are only capable of windage adjustments.  Elevation must be established with adjustments to the front sight.  Most backup sights do not have the fine adjustments like those on a carry handle.  Zero them as close as possible, but don’t expect perfection.  Zero your backup sights for point-of-aim / point-of-impact at 50 yards.  Be sure to use Loctite thread locker when mounting your backup sights.  I promise that the screws will eventually loosen during shooting and will lose their zero.  More details are discussed further down with Flat-Top Rifles With Backup Iron Sights (BUIS).



Non-Magnified Red-Dot Sights & Holographic Sights On The AR-15:

Red-dot and holographic sights make it much easier to quickly acquire and hit targets than “iron sights”.  Shooting from CQB distances out to 300 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.

Unless the optic is equipped with some type of bullet drop compensation (BDC) then you will want to zero the optic for point-of-aim / point-of-impact at 50 yards. Be sure to use Loctite thread locker when mounting your optic. I promise that the screws will eventually loosen during shooting and will lose their zero.

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 set of backup sights (discussed above) as batteries can go dead and electronics can fail or be destroyed. With backup sights you will be able to stay in the fight.

Unless the optic is equipped with some type of bullet drop compensation (BDC) then you will want to zero the optic for point-of-aim / point-of-impact at 50 yards.  More details are discussed further down with What Distance to Zero Non-Magnified Optics & Sights.


Co-Witness Iron Sights and Optics:

Co-witness means that with your backup sights match up with your primary optic.  Your aiming reticle will appear to bisect the top of the front sight post.  It is easy to co-witness backup sights if you first zero your primary optic.  After the primary optic is zeroed, simply raise the backup sights into shooting position.  After verifying that the weapon is unloaded, aim the rifle at a point approximately the same distance that the rifle is zeroed (50 yards).  Using a front sight tool for the front sight, and the adjustment knob for the rear sight, you will want to adjust your backup sights so that the reticle of the already zeroed primary optic is bisected by the top of the front sight post of the backup sight.  Keep your co-witnessed backup sights folded down until needed.  More details are discussed further down with Co-Witness Iron Sights and Optics.


Magnified Optics On The AR-15:

Non-magnified red-dot and holographic optics are perfect for shooting at targets less than 250 – 300 yards, but at greater distances you will be greatly aided with a magnified optic.  Typically the greater the magnification, then the less the field of view, or the less that you will be able to see left and right of your target, thus degrading your situational awareness.  This is not good for combat / defensive shooting.  1-4x variable magnification optics are great for targets out to 300 to 500 yards, although man-size targets at 500 yards are pretty small.  If you plan on routinely shooting at targets 500 yards and beyond then you might benefit from a 1-6x variable magnification optic.  More details are discussed further down with Magnified Optics On The AR-15.  More magnified optics information is available on Savannah Arsenal’s Tactical Rifle Optics page.


Magnified Optics On The AR-15:

Non-magnified red-dot and holographic optics are perfect for shooting at targets less than 250 – 300 yards, but at greater distances you will be greatly aided with a magnified optic. 1-4x variable magnification optics are great for targets out to 300 to 500 yards, although man-size targets at 500 yards are pretty small with only 4x magnification. If you plan on routinely shooting at targets 500 yards and beyond then you might benefit from a 1-6x variable magnification optic. Keep in mind that 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 magnification. Examples of magnified optics are also discussed on the page linked above.


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 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 it written down.


Magnified Optics with Simple Crosshairs or Reticle:

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

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Sighting and Optic Options For Flat-Top AR-15 Rifles:

Improved Battle Sight Zero For Carry Handles With Adjustable Sights:

This applies to those with rifles equipped with fixed carry handle rear sights, or removable carry handle rear sights that adjust for both windage and elevation.

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. Early Battle Sight Zero techniques don’t 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.

Potential Problems Zeroing Rear Backup Sight and Optic:

F marked FSBThe vast majority of BUIS are manufactured to match the height of a Mil-Spec front sight base (FSB). If you want to add a Mil-Spec carry handle or a BUIS to a rifle with a shorter “commercial” grade (non-Mil-Spec) front sight base (FSB), then you will have to replace the stock front sight post with a slightly taller part. If you don’t, then you will not be able to raise your front sight post enough to zero the rifle. Details and solutions to the problem are discussed further down with Potential Problems Mounting and Zeroing Backup Sights. None of this is an issue if your rifle has a “F” marked (Mil-Spec height) front sight base (as seen right), or is completely flat-top and requires both a front and rear backup sight, as discussed next.


Front and Rear Flat-Top Configuration:

M4 ORCWhile some flat-top rifles will be manufactured with the traditional triangle FSB, others may be manufactured a rail on top of the gas block so that you can add a backup sight of your choice. Most front backup sights will fold down and out-of-the-way until you need them. This rifle configuration is sometimes referred to as an Optic Ready Carbine (ORC).

Daniel-Defense-AR-15-Flattop-DDM4-V11Some AR-15 rifles are manufactured or modified to have a railed forend that extends and covers where the triangle front sight would normally sit.


You can mount backup a backup rear sight where it should go, and then mount a front sight all of the way forward on the rail (as seen in the photo to the right). You can simply use the backup sights exclusively, or if you mount an optic, the front and rear backup sights can be folded down and out-of-the-way until they are needed (primary optic becomes inoperative).

If you use the front and rear backup sights exclusively, or use a non-magnified red-dot or holographic optic then you will want to zero your rifle so that the bullet impacts where you aim at 50 yards. This will give you the flattest trajectory possible with 5.56mm (.223 Remington) ammunition fired from a rifle with sights that sit 2.4″ to 2.5″ above the center of the bore. For further explanation, skip down to What Distance to Zero Non-Magnified Optics & Sights.


Backup Iron Sights (BUIS) Use On Flat-Top Rifles:

If you use the front and rear backup sights exclusively, or use a non-magnified red-dot or holographic optic then you will want to zero your rifle so that the bullet impacts where you aim at 50 yards. This will give you the flattest trajectory possible with 5.56mm (.223 Remington) ammunition fired from a rifle with sights that sit 2.4″ to 2.5″ above the center of the bore. For further explanation, skip down to What Distance to Zero Non-Magnified Optics & Sights.

If you are going to use a non-magnified red-dot or holographic optic, first zero your optic and then zero your BUIS. Your optic has much finer adjustments than the BUIS. As stated above, zero your optic so that the bullet impacts where you aim at 50 yards. Zeroing your BUIS is as simple as looking through your deployed sights with your correctly zeroed optic turned on. Adjust the backup sights so that the optic’s reticle dot is bisected by the tip of the front sight post. You don’t have to fire a shot to zero the backup sights, although prudence would suggest that you verify your zero on the range with your optic turned off. Keep in mind that since the backup sights do not have as fine of adjustments as the optic that you might not be able to get the sights perfectly aligned with the optic. This is okay. Just get it close enough. They are backup sights. They won’t be perfect, but they will be close enough that you can continue the fight if your optic fails.

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What Distance to Zero Non-Magnified Optics & Backup Sights:


Battle Sight Zero = Set It And Forget It:

Simply defined, “Battle Sight Zero” (sometimes referred to as “Battle Zero”, “BSZ”, or “BZ”) is a theoretical “set it and forget it” setting for your backup sights or non-magnified optics that will allow your to make combat effective hits out to a certain distance without applying any hold-over or hold-under from your point-of-aim. With your sights set to a “Battle Sight Zero” you will know that your rounds will hit no more than “X” inches above or below your point-of-aim from CQB distances out to “Y” yards or meters distance. 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.


What Zero Distance Provides 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. While you can expect minor variations in trajectory depending on if you are using a carbine with a 16″ barrel or a full-size battle rifle with a 20″ barrel, as we as with different brands, loads, and weights of ammunition, the data supplied is accurate enough to compare trajectories for use with backup sights and non-magnified optics.

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 a second 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 (109 yards) the your rounds will impact over 4″ above your POA. At 175 meters the bullet impact will reach its peak apogee 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 (not meters). 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 apogee 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 backup sights and non-magnified optics as a “set it and forget it” Battle Sight Zero setting.



The 50 yard zero provides the flattest trajectory for the AR-15 style rifle. 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 of approximately 250 yards. Competitive shooters and the USMC now realize this and employ the 50 yard zero technique with backup sights and non-magnified red-dot and holographic optics.

Important: This Battle Sight Zero is for AR-15 style rifles firing 5.56mm NATO ammunition. It is not necessarily an appropriate Battle Sight Zero for other 5.56mm rifles (because they may have sights of different height over bore than the AR-15), or rifles in other calibers. This is not the correct zero for Tavor, Steyr AUG, or AK rifles chambered in 5.56mm.


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Co-Witness Backup Sights and Optics:

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”.

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 reticle is horizontally bisected by the tip of the front sight post.

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AR-15 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:

Using either a dedicated .22LR upper receiver or a .22LR conversion kit is a great way to teach a new AR shooter the fundamentals of shooting the rifle without the intimidating loud noise of the full size battle ammunition, and for the experienced shooter to maintain proficiency at a fraction of the cost of shooting full size .223/5.56 ammunition.

To shoot .22LR ammunition out of an AR platform, you basically have two options. You can buy a dedicated upper receiver/barrel set, or buy a .22LR conversion kit that simply replaces your bolt carrier and fires the .22LR bullets through your AR barrel. The dedicated upper’s barrel will usually be a 1 in 12″ twist (as opposed to your AR’s 1 in 7″ or 1 in 9″ twist). The 1 in 12″ twist will result in a better stabilized .22LR bullet in flight which may result in slightly better accuracy. .22LR rounds fired from a conversion kit and through your AR’s barrel may or may not be as accurate as those fired out of a dedicated upper, but I have been very satisfied with the results using the simple and less expensive conversion kit. I can easily hit coke cans at 50 yards, and a full size paper plate at 100 yards. This is good enough for training purposes.

I live and swear by my CMMG brand .22LR conversion kit. When properly maintained, it is both reliable and accurate. They are around $160 and usually come with a 25 round magazine.

For a thorough review, check out:

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AR-15 Related Website, Blogs, and Articles:

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Savannah Arsenal’s Related Pages:

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Final Recommendations:

  • 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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3 comments on “AR15 / M4 / M16

  1. Issues, runs dirty, jams & failures to eject spent cartridges. American made rifle, low quality.


    • That is a by far the most ignorant statement that someone has attempted to post here. Normally I edit out the Call of Duty “armchair commando” trolling comments, but I had to leave this one on here for laughs.

      I’ve owned at least 10 different rifles (5 different manufacturers) and fired tens of thousands of rounds through them. I have had one failure to eject (with steel case ammo in a very hot gun), and never a failure to fire. The rifle system has been reliably putting bad guys in the ground for over half of a century.

      …and if you are trying to belittle American made firearms, keep in mind that the US military’s rifles are made by FN of Belgium. Eurotrash bastard children of an American icon.


  2. 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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