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Nomenclature Of The AR-15 Rifle
Contributed by Ken Russo

NOMENCLATURE

Weapon description:

    - 5.56MM NATO Chambering Gas operated, magazine fed internal recoil buffer (weighted) Steel rotating multi-lug bolt and bolt carrier

    - Magazine- factory 20-30 round magazines.

    - Receiver - aluminum upper and lower, gray phosphate Mil-Spec non reflective, non-self lubricating finish.

    - Barrel- Chrome moly steel/chrome lined bore and chamber.

    - Available barrel twists: 1 in 7”, 1 in 9”, (1 in 8” supplied in most competition rifles with addition of commercial 223 Rem chambering alone with
    variants like 223 Wylde for use with 75-80grain projectiles)

    - Barrel lengths: 10.5”, 14.5”, 16”, 20” and 24”

    - Synthetic stock- fixed and retractable, synthetic 2 piece hand guards Stainless steel gas tube

    - Sights: A1 original design, non-elevation adjustable rear sight with use of a tool. A2 Knob Adjustable windage and elevation rear sight. A3
    Adjustable as A2 + removable carry handle (flat top). Front sight: Bladed square post, elevation adjustable with tool.

    - Forward Assist/right hand ejection/built in brass deflector on A2 and newer models (A1 models lack brass deflector and forward assist)

    - Threaded flash suppressor or crowned barrel end on post-ban rifles

Ammunition/Chambering

Most people often mistake the designations of 223 Remington and 5.56mm
NATO chambers as being completely interchangeable. Listed here are the differences between the two chamberings.

223 Remington: Commercial (civilian) chambering most often found in AR15 rifles with a Match chamber and in non mil-spec rifles. 223 Remington chambers are set up with tighter internal tolerances and require the use of 223 Remington commercial ammunition only. There are many available variants of the standard 223 Remington chambering as in the following examples. It does not name all but just a few.

     223Remington Standard Chamber
     223Remington Match
     223Remington - Wylde (Competition chambering offered by Rock River Arms)
     223Remington (Savage Arms Match chamber)

- 5.56mm NATO: Mil-Spec chamber (More generous dimensions than standard 223 Remington Commercial chambering), chrome lined chamber and bore for resistance to corrosion in harsh environments. Improved feeding and extraction during rapid fire/full auto operation or from extended periods of abuse/zero maintenance in military combat environments.

5.56mm NATO chambered rifles will reliably function with either 223 Remington commercial ammunition or 5.56mm NATO military M855 62gr ball or older (Pre-1982) 55gr NATO ball ammunition. Firing 5.56mm NATO ammunition in a 223 Remington chamber can lead to pressure related problems due to tighter neck dimensions in 223 Remington chambers and thicker case walls in 5.56mm NATO spec brass.

Some of the problems related to pressure are the possibility of blown primers, ripped case rims leading to extraction problems and excess wear and tear on internal parts possibly leading to parts or weapon failure.

Any ammunition intended for street use must be tested for reliability in any gas operated weapons. Barrel lengths and gas port setup make a difference in reliability from commercial AR15 and military M16 setups.

Generally most AR15/M16 based rifles come with either a 1 in 9” or 1 in 7” twist barrel. The 1 in 7” twist barrels will allow the use of 40-80 grain projectiles. Currently 80 grain projectiles are not commercially available as loaded ammunition.

Barrels with a 1 in 9” twist will allow shooting of 40-75 grain bullet weights. Since most commercial 223 ammunition choices fall within 55-62 grains, a 1 in 9” barrel is a good choice. 1 in 9” barrels produce better accuracy with these bullet choices.

Barrel life is also generally longer than on 1 in 7” barrels because the faster twist combined with use of heavier bullets causes more throat erosion. Either twist is generally suitable for close range urban use.

Barrel lengths of less than 16 inches are also reliant upon proper gas port system setup and proper ammunition selection. Short gas tube systems require slightly oversized gas ports for reliable feeding and extraction. Use of heavier bullets with short-barreled rifles also increased the reliability of function from 14.5” and shorter rifles.

Heavier bullets are moving slightly slower and remain in the barrel long enough to develop the pressure necessary to reliably operate the gas system. Lighter bullets generally exit the barrel too quickly to guarantee high enough pressure to reliably operate the gas system. Opening the gas port to allow more gas pressure in short barreled rifles will alleviate this problem, but this should only completed by a competent gunsmith or by factory service.

With the wide variety of ammunition available for law enforcement use today, it is best to select ammunition, which reliably performs in the weapons, and predictably performs on a variety of mediums such as automotive glass, barriers and windows. The only way to be sure is to actually test ammunition side by side and make an informed decision after testing.

Many of the manufacturers claim their ammunition to be “TACTICAL” use ammo, but it is more of a sales pitch that has to be tested for actual performance. Varying bullet design will show which ammunition keeps its bullet integrity after passing through such test mediums. It should also be pointed out that as a general rule, 223 ammunition performs exceptionally well on automotive and domestic house glass. Tests show that there is generally mush less deflection with the 223 than with .308 Winchester ammunition.

Once a suitable 223 caliber bullet design/weight is chosen, it can be relied upon to work well against such intermediate barriers. It is not to suggest that the 223 be selected to replace the .308 Winchester as a primary sniper round, since the 223 lacks the stopping power to be relied upon in this capacity.

There have been many incidents documented where a sniper rifle in 223 was employed and the 223 was shown to be less than effective in this role with an off center shot. Sniper rifles and ammunition need to be selected for their ability to deliver a shot that can instantly incapacitate an adversary. A 223 caliber patrol carbine is not the weapon for such a task.

Ammunition available is found in 40-75 grain weights from a variety of manufacturers and individual bullet designs are just as varied within each bullet weight. There are full metal jacket (FMJ), jacketed hollow point (JHP), lead soft point (SP), and newer nylon tipped hollow cavity (Nosler Ballistic Tip or Hornady V-Max) designs just to name a few.

Within each bullet design there are also varied weight offerings depending upon the intended use of the ammunition. Generally the 55gr FMJ ammunition works well on all intermediate barriers, but the downside of this is the high potential for over penetration on both barriers and human targets. The use of FMJ ammunition should be avoided for weapons in an urban environment. The AR15/M16 generally feeds all known commercial and military ammunition very reliably and more reliably than in Ruger Mini-14 rifles in use with the Department. The added reliability of the AR15 comes from the incorporation of feed ramps at the chamber opening, which the Mini-14 does not have. When Ruger designed the Mini-14 after the Springfield M14, the feed ramps found on the M14 were not incorporated into the Mini. Without the feed ramps, the Mini-14 will have a shorter list of ammunition that is suitable for field use and soft point ammunition is generally not a good choice for the Ruger.

Sights

Rear peep, adjustable for elevation and windage. Adjustments are usually ¼”, ½” 1/3” (MOA) depending upon the manufacturer and purpose of the rifle. ½” MOA is most often found on AR15/M16 based rifles. ¼” MOA adjustments are usually a special request for 20” barreled service rifles used in competition. Fine adjustments are usually no advantage on rifles with less than 20” barrels since the sight radius is too short to take full advantage of the system. ½” adjustments are more than adequate for the task of the tactical patrol carbine.

The rear sight aperture has two flip up peep holes. The use of the smaller diameter hole allows for more accurate fire due to a finer sight picture. The larger aperture is primarily designed for combat use allowing quicker sight acquisition and better sight picture in low light situations. (This sight system also offers a distinct advantage over rifles like the Mini-14 which incorporates a small rear peep sight aperture that is virtually impossible to acquire a proper sight picture with in low light situations.)  For use as a tactical patrol carbine it is recommended that the larger aperture be used on a full time basis although some reduction in accuracy will be realized.

Front sight: Square post type, adjustable for gross elevation. Sight post is protected by two blades, the front sight base is part of the gas system, which covers the gas port in barrel and serves as the transfer point for cartridge gasses to pass through the sight base and into the gas tube assembly.  The adjustment of this front sight should be limited to adjustments to zero that cannot be made by utilizing the rear sight adjustments.

Charging Handle

Located at the upper forward end of the butt stock, the charging handle is engaged by pinching and releasing the catch on the left side of the handle and drawing the handle sharply in a rearward motion. Releasing the handle allows the bolt to close chambering a live cartridge. The charging handle is also used to eject any live cartridges from the chamber and to hold the bolt open until the bolt stop is employed. When keeping the bolt open, always push the charging handle forward to lock it back in place. Due to its design, the AR15/M16 charging handle is one of the weak links to the system and care must be taken to prevent damage to it. Proper familiarization with the unit and its operation will ensure that operator error with use of the charging handle will not become a factor.

Light lubrication of the charging handle will also insure reliable operation. The procedure for this will also be covered in the care and maintenance phase. As an add on item, the charging handle can be equipped with an oversized tactical latch which can make operation of the rifle more reliable if using gloves of if a particular sighting system prevents ease of operation. Such a modification must be approved by the Department gunsmiths.

Magazines

AR15/M16 magazines are aluminum shelled box type in 20 and 30 round configurations for law enforcement only due to federal legislation (1994 assault weapons ban). Twenty round magazines feed most reliably because the follower does not have to make a turn in the magazine body. Twenty round magazines are easier to carry and thus allow a shooter to fire from the prone position without interference from the floor. Other magazine types are available but not recommended. Orlite, Thermold and other aftermarket military type magazines are readily available, but if a magazine system other than factory is to be used, they must be tested for reliability prior to deployment in the street.

Magazine Release

The magazine release button is operated from right hand side of lower receiver.  No secondary magazine release is available on AR15/M16 based weapons as on H&K MP5 type weapons.

Weapon Finish

AR15/M16 based weapons are finished in a non-reflective gray phosphate military specification, corrosion resistant, non-self lubricating finish. Lubrication will be addressed during the care/maintenance phase.

Trigger

AR15/M16 based rifles are equipped with either a single stage or two stage trigger system. Two stage trigger systems allow better feel and deliver more feedback to the shooter and are more commonly found on competition rifles. Some current AR15/M16 M4 variants are being produced with 2 stage match triggers but the majority comes with a single stage trigger system.

AR15 and M16 rifles differ in that an AR15 rifle system is semi-automatic only and the M16 platforms are select fire weapons offering semi-auto and either burst or full automatic fire capability via a selector switch.

Trigger weights as supplied from the factory often vary but ideally a trigger pull weight of no less than four pounds is desirable. Single stage triggers in general are more than adequate for this type of weapon.

Flash Suppressors

AR15/M16 based rifles generally come with an A2 birdcage type flash suppressor. Birdcage type suppressors in the A2 configuration have a solid bottom with 5-vented slots on the upper half of the unit. The solid bottom prevents muzzle blast from kicking up dust when firing from the prone position.

Newer designs are multi-directional and cool flame quicker and reduce muzzle flash by more than 80% versus older A2 designs. Examples of these are the Smith Enterprise Vortex and Phantom designs. Both Vortex and Phantom suppressors effectively defeat flash signatures, but Phantom suppressors have a closed end. Low light firing conditions can cause flash signatures to become a factor with retention of an officer’s night vision capability, depending upon the sensitivity of the officer to the muzzle flash of the weapon.

Rifles built to post-ban civilian legal configurations have either a plain crowned barrel or a permanently attached muzzle brake per 1994 Crime Bill regulations.

Crowned 16” barrels with no suppressor or muzzle brake typically exhibit a large muzzle flash during fire because of unburned powder exiting the barrel upon bullet exit. Short 16 inch barrels often have the largest muzzle flash signature and it often depends upon the ammunition used.

Varying powder types will dictate the severity of the muzzle flash. Rifles equipped with muzzle brakes are typically louder than their counterparts with just a suppressor or nothing at all. Muzzle brakes reduce felt recoil by redirecting muzzle gasses but increased noise is the result.

Design of the AR15 based rifles already reduce felt recoil and muzzle brakes are not recommended. The best option for law enforcement rifles is to obtain pre-ban configuration rifles with just A2 flash suppressors or aftermarket Vortex or Phantom units.

Sling systems

AR15/M16 rifles typically come with a simple one-inch shoulder sling supplied by the manufacturer. These are typically not long enough for anything but simple shoulder carry.

Single and three point tactical slings are readily available from a variety of manufacturers and are more suited to this application of the rifle. Use of a tactical three-point sling allows for operators to readily transition to secondary weapons and also allows the operator to keep his hands free to perform tasks without having to worry about loosing control of the weapon.

Use of a single point sling system generally requires the installation of a single point sling adapter, which is a gun shop modification. The adapter adds a loop to the center of the rifle at the beginning of the buffer tube assembly which allows easy connection of the single-point type sling adapters available in ambidextrous setups for left handed sling setup.

Operation and deployment of a tactical rifle or carbine with only the use of simple loop sling is a disadvantage to the operator and restricts his use of the weapon platform in tactical situations. With the employment of either single or three point tactical slings, an emergency release buckle and a tension clip will allow the operator a wide variety of sling positions and a method of rapidly releasing the weapon sling if the need arises.  The addition of these features to a tactical sling does not compromise the safe deployment of this weapon system.

Butt Stocks

AR15/M16 based rifles come in two basic configurations. Fixed, non-adjustable butt stock and a retractable 4 or 6 position butt stock. Both types involve a self-contained recoil buffer system. Buffer weights vary with full sized rifle/M4 carbine/9mm carbine weapon systems.

Advantages of an adjustable stock:
- Allows for easy storage/transport of the carbine
- Allows for adjustability for body types of shooters/body armor
- A Rubber butt cap suggested with use of retractable stock to prevent slippage on clothing.

Article contributed by Ken Russo


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