Work In Progress

This article is still under construction. It may contain factual errors. See Talk:Colt AR-15 Identification Guide for current discussions. Content is subject to change.

This page is intended as a guide to identify the various Colt manufactured M16 variants and derivatives. This is not a complete list of all variants produced by Colt, and only contains those variants that have appeared in media. Due to the large number of companies that make AR-15 pattern rifles that are nearly indistinguishable from the original variants, all rifles should be identified using Colt terminology in the absences of any information to the contrary, such as unique parts or visible receiver markings.

Weapon Name	Model Number	Upper Receiver	Lower Receiver	Stock	Barrel Length	Barrel Profile	Flash Hider	Bayonet Lug
M16	602	Slickside	Slabside	Solid fixed	20"	A1	Duckbill	Yes
XM16E1	603	A1	Partial fence	Solid fixed	20"	A1	Duckbill	Yes
M16A1	603	A1	Full fence	A1 fixed	20"	A1	A1	Yes
USAF M16	604	Slickside	Partial fence (early) Full fence (late)	A1 fixed	20"	A1	Duckbill (early) A1 (late)	Yes
CAR-15 SMG	607	Slickside (607) A1 (607A)	Partial fence	1st gen. collapsible	10"	A1	3.5" moderator	No
XM177E1	609	A1	Partial fence (early) Full fence (late)	2nd gen. collapsible	10"	A1	4.5" moderator	No
XM177 or GAU-5/A	610	Slickside	Partial fence (early) Full fence (late)	2nd gen. collapsible	10"	A1	4.5" moderator	No
XM177E2	629	A1	Full fence	2nd gen. collapsible	11.5"	A1	4.5" moderator (Grenade ring)	No
GAU-5A/A	630	Slickside	Full fence	2nd gen. collapsible	11.5"	A1	4.5" moderator (Grenade ring)	No
9mm SMG DOE	633	SMG	Full fence	3rd gen. collapsible	7"	A1	None	No
9mm SMG	635	SMG	Full fence	3rd gen. collapsible	10.5"	A1	A2	Yes
M16A2	645	A2	Full fence	A2 fixed	20"	A2	A2	Yes
M16A1 Carbine	653	A1	Full fence	2nd gen. collapsible	14.5"	A1	A1	Yes
M16A1 Carbine	654	Slickside	Full fence	2nd gen. collapsible	14.5"	A1	A1	Yes
M16A1 Special High Profile	655	A1	Partial fence	A1 fixed	20"	HBAR	A1	Yes
M16A1 Special Low Profile	656	A1 flat top	Partial fence	A1 fixed	20"	HBAR	A1	Yes
M16A2 or Diemaco C7	715	A1E1	Full fence	A2 fixed	20"	A2	A2	Yes
M16A2 Carbine	723	A1E1	Full fence	3rd gen. collapsible	14.5"	A1	A2	Yes
M16A2 Carbine	727	A2	Full fence	3rd gen. collapsible	14.5"	M4	A2	Yes
M16A2 Commando	733	A1 (early) A1E1 (early) A2 (late)	Full fence	3rd gen. collapsible (early) 4th gen. collapsible (late)	11.5"	A1 or A2	A1 or A2	Yes or no
M16A2 LMG or Diemaco C7 LSW	750	A2 LMG	Full fence	A2 fixed	20"	LMG	A1	No
M4	920	Flat top	Full fence	3rd gen. collapsible (early) 4th gen. collapsible (late)	14.5"	M4	A2	Yes
M4A1	921	Flat top	Full fence	4th gen. collapsible	14.5"	M4	A2	Yes
M4 Commando	933	Flat top	Full fence	3rd gen. collapsible (early) 4th gen. collapsible (late)	11.5"	A1 or A2	A2	Yes or no
M16A4	945	Flat top	Full fence	A2 fixed	20"	A2	A2	Yes
M16A3 LMG or Diemaco C7A1 LSW	950	Flat top LMG	Full fence	A2 fixed	20"	LMG	A2	Yes
9mm SMG	991	Flat top SMG	Full fence	4th gen. collapsible	10.5"	A1	A2	Yes
M231	None	Slickside (sightless)	Full fence	None	15.6"	A1	A1	No
AR15 Sporter (SP1)	R6000	Slickside	Slabside (screw pin)	Solid fixed (early) A1 fixed (late)	20"	A1	A1	Yes
AR-15 Sporter (SP1) Carbine	R6001	Slickside	Slabside (screw pin)	3rd gen. collapsible	16"	A1	A1	Yes
AR-15A2 Sporter II Carbine	R6420	A1 (early) A1E1 (late) A2 (last)	Slabside (screw pin)	2nd gen. collapsible (early) 3rd gen. collapsible (late)	16"	A1	A1 (early) A2 (late)	Yes
AR-15 9mm Carbine	R6450	SMG	Full fence	3rd gen. collapsible	10.5"	A1	A1	Yes
AR-15A2 Sporter II	R6500	A1 (early) A1E1 (late) A2 (last)	Slabside (screw pin)	A2 fixed	20"	A2	A2	Yes
AR-15A2 Government Carbine	R6520	A2	Full fence	3rd gen. collapsible	16"	A1	A2	Yes
AR-15A2 Sporter Lightweight	R6530	A2	Full fence	A2 fixed	16"	A1	A2	No
AR-15A2 HBAR	R6550	A2	Full fence	A2 fixed	20"	HBAR	A2	Yes
AR-15A2 Government Carbine	AR6520	A2	Full fence	4th gen. collapsible	16"	A1	A2	Yes
AR-15A3 Tactical Carbine	AR6721	Flat top	Full fence	4th gen. collapsible	16"	HBAR	A2	Yes
Match Target HBAR	MT6601	A2	Full fence	A2 fixed	20"	HBAR	Target crown	No
Match Target Competition HBAR	MT6700	Flat top	Full fence	A2 fixed	20"	HBAR	Target crown	No
Match Target HBAR II	MT6731	A2	Full fence	A2 fixed	16"	HBAR	Target crown	No
Law Enforcement Carbine	LE6920	Flat top	Full fence	4th gen. collapsible	16"	M4	A2	Yes

Glossary

Upper Receivers

Slickside

The earliest version of the AR-15 upper receiver which can easily be identified by its lack of forward assist and brass deflector. This receiver was used on the original M16, USAF weapons, and the SP1 civilian rifle.

A1

The first variant to be fitted with a a forward assist (which has a tear-drop shaped plunger head as opposed to the round plunger used on later rifles). This is the only upper to feature a forward assist without brass deflector.

A1E1

An intermediate receiver that was an A1 receiver with the addition of a brass deflector behind the ejection port. It can be distinguished from the A2 receiver by its simpler rear sight. This upper was the one that was chosen by Diemaco (now Colt Canada) for the C7 rifle and C8 carbine. It was also commonly used on the Model 723 and 733 carbines.

A2

This upper was first implemented on the M16A2. It notably differs from its predecessor, the A1 upper, by the addition of a brass deflector and a more complicated range adjustable rear sight.

Flat Top

Essentially an A2 upper with the fixed carry handle replaced with a MIL-STD-1913 scope rail. It can often be seen fitted with a carry handle of the same design as the A2 upper. This is the upper that is used on the majority of current military, law enforcement and civilian rifles.

A2 LMG

A unique upper receiver fitted only to the Model 750. Externally it appears as an A2 upper with the forward assist omitted (being an open bolt weapon, a forward assist would be redundant).

Flat Top LMG

A unique upper receiver fitted only to the Model 950. Externally it appears as a flat top upper with the forward assist omitted (being an open bolt weapon, a forward assist would be redundant).

SMG

The upper receiver used on the 9x19mm submachine guns and carbines is actually a modified slickside upper, fitted with a distinctive semi-circular brass deflector over the rear of the ejection port (which is pinned to the receiver and removable, as opposed to the integrally forged one found on 5.56x45mm rifles) and a correspondingly shortened dust cover.

Flat Top SMG

A flat top variant of the original SMG upper with the same removable brass deflector, this is the upper which is used on the current range of submachine guns and carbines.

Slickside (Sightless)

A unique upper receiver found only on the M231 firing port weapon. It is identical to the slickside upper used on the original M16 but features no rear sight, being designed to be aimed using tracer fire. It does however retain the carry handle that the rear sight is normally mounted in along with the windage direction arrows for adjusting the absent sight, due to it being made from a regular slickside forging without the final machining for the rear sight.

Lower Receivers

Slabside

Used only on the AR-15 prototypes and the original M16, the slabside lower can be identified by the lack of any ridges on the right side of the weapon. The push pin as the front of the lower receiver either has a flat round head, or a round head with a circular divot in the centre.

Slabside (Screw Pin)

A variant of the slabside receiver with a screw pin at the front of the receiver is used on early Sporter models up to the AR-15A2 Sporter II. This variant of the slabside lower receiver is much more common than the genuine military slabside lower, meaning it is often used as a stand in for the correct M16 lower receiver in television and movies.

Partial Fence

Most notably used on the XM16E1, although also used on a number of contemporary carbines and experimental weapons, the partial fence lower features a horizontal ridge under the ejection port, a captive push pin at the front pivot, and an unfenced magazine release button. The term partial fence is a misnomer as the ridge on the side of the receiver is unrelated to the magazine release button, but is instead a housing for the detent spring which retains the new push pin. The partial fence name has only been applied retroactively in relation to the later full fence lower.

Full Fence

The full fence lower is the standard receiver used on all AR-15s since the M16A1. It can be identified by the raised fence around the magazine release button on the right side of the weapon which is designed to lessen the chances of accidentally releasing the magazine. The design of this lower was upgraded with the adoption of the M16A2 featuring strengthening around the front and rear receiver push pins and fire selector marking on the right side of the receiver. However, due to the difficulty in identifying them from a distance and the fact that different manufacturers use slightly different designs (such as strengthening around only the front push pin or omitting the selector markings on the right side of the weapon), these have been treated as one variant for the purpose of identification.

Stocks

Solid Fixed

A solid stock without an internal storage compartment and one piece butt pad was used on rifles prior to the M16A1. This stock can also be identified by hinged rear sling loop.

A1 Fixed

The M16A1 introduced an internal storage compartment into the stock accessed by a textured trapdoor in the butt pad. The original hinged rear sling loop was also replaced by a simpler and more robust fixed loop.

A2 Fixed

The M16A2 used a new stock that was slightly longer (16mm, nearly indistinguishable to the regular observer) and made from a much stronger material. The easiest may to differentiate this stock from that found on the M16A1 is the squarer edges on the butt pad, and the fact that the butt pad is chequered over it entire surface (as opposed to the A1 stock which was only textured on the trapdoor cover).

1st Generation Collapsible

This stock resembles a miniature fixed stock, but can be extended by operating a lever inside the butt pad. The only weapon it was used on was the Model 607 Car-15 SMG, and was abandoned for a simpler, cheaper and more robust design for all future carbines.

2nd Generation Collapsible

A stock made from aluminium with a black polymer coating was used on the majority of carbines from the Vietnam war until 1985.

3rd Generation Collapsible

This stock was introduced in 1985 and is commonly known as the "fiberlite stock". The shape is similar to the early coated aluminium stock but was made from plastic, and can be differentiated by its matt finish (the coated aluminium stocks had a shiny black finish) and the two vertical strengthening ribs on each side. Early models were only two position stocks, but later models were four position.

4th Generation Collapsible

Often called the "M4 stock" or "6 position" stock, this was developed as a strengthened variant for use on the M4/M4A1 carbines. It features a number of ridges and recesses on the sides of the stock, a sloped butt plate and the same bottom mounted sling loop found on M16A1/A2 fixed stocks.

Wire Collapsible

Developed for emergency dismounted use on the M231 firing port weapon, this wire stock is similar to the one found on the M3 / M3A1 "Grease Gun". Although designed for the M231, it can be fitted to any AR-15 pattern rifle.

Flash Hider

Early Duckbill

The original AR-15 flash hider, referred to as the “Duckbill”, was only seen on early prototypes. It was quickly abandoned due to the tendency of the front prongs to break off.

Duckbill

A strengthened variant of the early Duckbill flash hider, this could be seen on the majority of colt weapons prior to the M16A1.

A1

The iconic M16 flash hider often referred to as the “Birdcage”, and was on a closed design to address problems encountered with the duckbill type flash hiders snagging on vegetation. Introduced on the M16A1, it has 6 ports equally distributed around the flash hider.

A2

First developed for the M16A2, this flash hider is similar in appearance to the original birdcage except it features five ports spread only over the top half of the flash hider. Although often described as a compensator this was not the intended purpose of the modification, but was instead designed to reduce the amount of material that would be kicked up by the muzzle blast when firing in the prone position.

3.5" Moderator

Resembling a small sound suppressor, the 3.5” moderator was designed for the Model 607 (which originally used a duckbill flash hider) in an attempt to mitigate the large muzzle flash and blast created when using such a short barrel. It featured a number of internal baffles to reduce not only the flash but also the sound report, meaning it is classed as a suppressor making civilian use more legally problematic (due to this the majority of moderators seen in film and television are replicas omitting the internal baffles and chambers). Although it succeeded in reducing the flash somewhat it led to excessive fouling in the chamber, along with accuracy problems using tracers.

4.25" Moderator

An improved version of the 3.5” moderator, this features a slotted expansion chamber at the end further reducing the weapon report. The majority (although not all) of the moderators made featured a narrow section at the back with a rib behind it referred to as a “grenade ring” to allow mounting of an under-barrel M203.

Colt AR-15 Identification Guide