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VARMINTSDEN
AR-15 TECHNICAL INFORMATIONEXCHANGE

NomenclatureOf The AR-15 Rifle
Contributedby Ken Russo
NOMENCLATURE

Weapon description:

- 5.56MM NATO ChamberingGas operated, magazine fed internal recoil buffer (weighted) Steel rotatingmulti-lug bolt and bolt carrier

- Magazine- factory20-30 round magazines.

- Receiver - aluminumupper and lower, gray phosphate Mil-Spec non reflective, non-self lubricatingfinish.

- Barrel- Chromemoly steel/chrome lined bore and chamber.

- Available barreltwists: 1 in 7”, 1 in 9”, (1 in 8” supplied in most competition rifleswith addition of commercial 223 Rem chambering alone with
variants like 223Wylde 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 gastube

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

- Forward Assist/righthand ejection/built in brass deflector on A2 and newer models (A1 modelslack brass deflector and forward assist)

- Threaded flashsuppressor or crowned barrel end on post-ban rifles

Ammunition/Chambering

Most people often mistake the designationsof 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 aMatch chamber and in non mil-spec rifles. 223 Remington chambers are setup with tighter internal tolerances and require the use of 223 Remingtoncommercial ammunition only. There are many available variants of the standard223 Remington chambering as in the following examples. It does not nameall but just a few.

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

- 5.56mm NATO:Mil-Specchamber (More generous dimensions than standard 223 Remington Commercialchambering), chrome lined chamber and bore for resistance to corrosionin harsh environments. Improved feeding and extraction during rapid fire/fullauto operation or from extended periods of abuse/zero maintenance in militarycombat environments.

5.56mm NATO chambered rifles will reliablyfunction with either 223 Remington commercial ammunition or 5.56mm NATOmilitary M855 62gr ball or older (Pre-1982) 55gr NATO ball ammunition.Firing 5.56mm NATO ammunition in a 223 Remington chamber can lead to pressurerelated problems due to tighter neck dimensions in 223 Remington chambersand thicker case walls in 5.56mm NATO spec brass.

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

Any ammunition intended for street usemust be tested for reliability in any gas operated weapons. Barrel lengthsand gas port setup make a difference in reliability from commercial AR15and military M16 setups.

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

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

Barrel life is also generally longerthan on 1 in 7” barrels because the faster twist combined with use of heavierbullets causes more throat erosion. Either twist is generally suitablefor close range urban use.

Barrel lengths of less than 16 inchesare also reliant upon proper gas port system setup and proper ammunitionselection. Short gas tube systems require slightly oversized gas portsfor reliable feeding and extraction. Use of heavier bullets with short-barreledrifles also increased the reliability of function from 14.5” and shorterrifles.

Heavier bullets are moving slightlyslower and remain in the barrel long enough to develop the pressure necessaryto reliably operate the gas system. Lighter bullets generally exit thebarrel too quickly to guarantee high enough pressure to reliably operatethe gas system. Opening the gas port to allow more gas pressure in shortbarreled rifles will alleviate this problem, but this should only completedby a competent gunsmith or by factory service.

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

Many of the manufacturers claim theirammunition to be “TACTICAL” use ammo, but it is more of a sales pitch thathas to be tested for actual performance. Varying bullet design will showwhich ammunition keeps its bullet integrity after passing through suchtest mediums. It should also be pointed out that as a general rule, 223ammunition performs exceptionally well on automotive and domestic houseglass. Tests show that there is generally mush less deflection with the223 than with .308 Winchester ammunition.

Once a suitable 223 caliber bullet design/weightis chosen, it can be relied upon to work well against such intermediatebarriers. 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 stoppingpower to be relied upon in this capacity.

There have been many incidents documentedwhere a sniper rifle in 223 was employed and the 223 was shown to be lessthan effective in this role with an off center shot. Sniper rifles andammunition need to be selected for their ability to deliver a shot thatcan instantly incapacitate an adversary. A 223 caliber patrol carbine isnot the weapon for such a task.

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

Within each bullet design there arealso 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 onboth barriers and human targets. The use of FMJ ammunition should be avoidedfor weapons in an urban environment. The AR15/M16 generally feeds all knowncommercial and military ammunition very reliably and more reliably thanin Ruger Mini-14 rifles in use with the Department. The added reliabilityof 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 afterthe Springfield M14, the feed ramps found on the M14 were not incorporatedinto the Mini. Without the feed ramps, the Mini-14 will have a shorterlist of ammunition that is suitable for field use and soft point ammunitionis generally not a good choice for the Ruger.

Sights

Rear peep, adjustable for elevationand windage. Adjustments are usually ¼”, ½” 1/3” (MOA) dependingupon the manufacturer and purpose of the rifle. ½” MOA is most oftenfound on AR15/M16 based rifles. ¼” MOA adjustments are usually aspecial request for 20” barreled service rifles used in competition. Fineadjustments are usually no advantage on rifles with less than 20” barrelssince the sight radius is too short to take full advantage of the system.½” adjustments are more than adequate for the task of the tacticalpatrol carbine.

The rear sight aperture has two flipup peep holes. The use of the smaller diameter hole allows for more accuratefire due to a finer sight picture. The larger aperture is primarily designedfor combat use allowing quicker sight acquisition and better sight picturein low light situations. (This sight system also offers a distinct advantageover rifles like the Mini-14 which incorporates a small rear peep sightaperture that is virtually impossible to acquire a proper sight picturewith in low light situations.) For use as a tactical patrol carbineit is recommended that the larger aperture be used on a full time basisalthough some reduction in accuracy will be realized.

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

Charging Handle

Located at the upper forward end ofthe butt stock, the charging handle is engaged by pinching and releasingthe catch on the left side of the handle and drawing the handle sharplyin a rearward motion. Releasing the handle allows the bolt to close chamberinga live cartridge. The charging handle is also used to eject any live cartridgesfrom 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 tolock it back in place. Due to its design, the AR15/M16 charging handleis one of the weak links to the system and care must be taken to preventdamage to it. Proper familiarization with the unit and its operation willensure that operator error with use of the charging handle will not becomea factor.

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

Magazines

AR15/M16 magazines are aluminum shelledbox type in 20 and 30 round configurations for law enforcement only dueto federal legislation (1994 assault weapons ban). Twenty round magazinesfeed most reliably because the follower does not have to make a turn inthe magazine body. Twenty round magazines are easier to carry and thusallow a shooter to fire from the prone position without interference fromthe 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 betested for reliability prior to deployment in the street.

Magazine Release

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

Weapon Finish

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

Trigger

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

AR15 and M16 rifles differ in that anAR15 rifle system is semi-automatic only and the M16 platforms are selectfire weapons offering semi-auto and either burst or full automatic firecapability via a selector switch.

Trigger weights as supplied from thefactory often vary but ideally a trigger pull weight of no less than fourpounds is desirable. Single stage triggers in general are more than adequatefor this type of weapon.

Flash Suppressors

AR15/M16 based rifles generally comewith an A2 birdcage type flash suppressor. Birdcage type suppressors inthe A2 configuration have a solid bottom with 5-vented slots on the upperhalf of the unit. The solid bottom prevents muzzle blast from kicking updust when firing from the prone position.

Newer designs are multi-directionaland cool flame quicker and reduce muzzle flash by more than 80% versusolder A2 designs. Examples of these are the Smith Enterprise Vortex andPhantom designs. Both Vortex and Phantom suppressors effectively defeatflash signatures, but Phantom suppressors have a closed end. Low lightfiring conditions can cause flash signatures to become a factor with retentionof an officerÂ’s night vision capability, depending upon the sensitivityof the officer to the muzzle flash of the weapon.

Rifles built to post-ban civilian legalconfigurations have either a plain crowned barrel or a permanently attachedmuzzle brake per 1994 Crime Bill regulations.

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

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

Design of the AR15 based rifles alreadyreduce felt recoil and muzzle brakes are not recommended. The best optionfor law enforcement rifles is to obtain pre-ban configuration rifles withjust A2 flash suppressors or aftermarket Vortex or Phantom units.

Sling systems

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

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

Use of a single point sling system generallyrequires the installation of a single point sling adapter, which is a gunshop modification. The adapter adds a loop to the center of the rifle atthe beginning of the buffer tube assembly which allows easy connectionof the single-point type sling adapters available in ambidextrous setupsfor left handed sling setup.

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

Butt Stocks

AR15/M16 based rifles come in two basicconfigurations. Fixed, non-adjustable butt stock and a retractable 4 or6 position butt stock. Both types involve a self-contained recoil buffersystem. Buffer weights vary with full sized rifle/M4 carbine/9mm carbineweapon systems.

Advantages of an adjustable stock:
  • Allows for easy storage/transportof the carbine
  • Allows for adjustability for bodytypes of shooters/body armor
  • A Rubber butt cap suggested withuse of retractable stock to prevent slippage on clothing.

Article contributed by Ken Russo
 
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