Explanation of all the variations of AR15/M4's

[Dastook]

Can anyone suggest a good article that explains all, or many of the different varieties of AR 15/M16/M4. I am fairly new to the AR platform. I love all of the things you can do with it but am having trouble understanding all of the terminology that is displayed by the very knowledgeable members of this forum. For instance. I do not know the differences between the AR15 and the M4, and don't know what makes it an A2 or A1 etc. I'm going crazy trying to take it all in.

[Frens]

Can anyone suggest a good article that explains all, or many of the different varieties of AR 15/M16/M4. I am fairly new to the AR platform. I love all of the things you can do with it but am having trouble understanding all of the terminology that is displayed by the very knowledgeable members of this forum. For instance. I do not know the differences between the AR15 and the M4, and don't know what makes it an A2 or A1 etc. I'm going crazy trying to take it all in.

here is a good starting point

http://en.wikipedia.org/wiki/M16_rifle


btw, M16/M4 is used when talking about military/fullauto weapons: everything else is a AR15 (M16gery/M4gery)

[C4IGrant]

Can anyone suggest a good article that explains all, or many of the different varieties of AR 15/M16/M4. I am fairly new to the AR platform. I love all of the things you can do with it but am having trouble understanding all of the terminology that is displayed by the very knowledgeable members of this forum. For instance. I do not know the differences between the AR15 and the M4, and don't know what makes it an A2 or A1 etc. I'm going crazy trying to take it all in.

Generally speaking the term "M4" refers to the barrel profile (as it is setup to accept a grenade launcher). A civy M4 and an AR15 are almost identical and the two terms are generally inter-mixed by most people.

An A1 receiver is a fixed carry handle without the elevation wheel for the rear sight. An A2 receiver is a fixed carry handle WITH the elevation wheel for the rear sight. An M4 receiver is a flattop with M4 cuts in it to line up with a M4 barrel extension.


C4

[Failure2Stop]

Generic Military designations

M16- The original. Triangular handguards; three-prong flash suppressor; safe, semi, auto; fixed carrying handle; battle sights; 1:12 twist rate; 20" barrel

M16A1- Product improved M16. Changes- Forward assist; bird-cage flash hider

M16A2- 1:7 twist rate; fine adjust sights (A2 sights); longer buttstock; ribbed tubular handguards; safe, semi, 3-round burst; A2 flash suppressor (birdcage with closed bottom); finger bump pistol grip; case deflector (thanks rmecapn).

M16A3- Same as A2, but with A1 type fire control (safe, semi, auto); some with removable carry handle/A2 sights/ picatinny railed upper.

M16A4- Same as A2 but with removable carrying handle/A2 sights/picatinny upper; Knight's M5 RAS railed handguard

M4- Essentially an A2 with a 14.5 inch barrel and correspondingly shortened tubular handguard and a collapsable/adjustable buttstock. Most have now been modified or ordered with railed upper/removable carry handle and Knight's M4 RAS. M4 profile barrels have a distinct groove machined in the barrel just forward of the front sight to accept the M203 grenade launcher. The M4 introduced "M4 Feed-Ramps" in which the upper receiver and barrel extension have deeper relief of the feed-ramps to improve feeding with the more violent cycling of the shortened gas-system.

M4A1- Same as M4 but with all the modifications (RAS, flat-top upper) and a safe, semi, auto trigger group. Some have a heavier barrel profile under the handguards to delay over-heating

Mk18/CQBR- Navy designation of the Commando. Essentially a 10.5 to 12.5 inch barrelled M4A1. Heavier buffer than the M4 to ensure proper operation.

Mk12 (Mod 0/Mod 1) / SAM-R - Army and Marine version of similar concept- precision rifle outwardly similar to a normal M16A4. Varying components between the two, but equipped with a free-floating handguard (Knight's on some SAM-Rs, PRI carbon-fiber on Mk12, later Knight's free-float), a Leupold Mk 4 MR/T scope, and usually Harris Bipods. The SAM-R has a fixed A2 style buttstock while the Mk12 may have a fixed A2 buttstock or a collapsable stock of several types. The venerable Mk 262 (Mod 0 and Mod 1) were designed for the Mk 12, though it has found favor with all types of M16 variants. They generally feature match-grade triggers of the safe, semi, auto option.

Commercial-
A2/A3 is frequently used to describe the type of upper receiver/carrying handle. A2 means fixed A2 style carrying handle and sighting system, while A3 usually denotes a flat-top upper, sometimes including the detachable carrying handle/rear sight.

M4 (aka M4geries) are usually 16" barrelled guns due to NFA regulations on barrels of shorter length. They usually have the M4 feed-ramps, though the quality and alignment of upper and barrel extension will vary with manufacturer QC. Some manufacturers will produce 14.5" barrels with a pinned and welded flash hider that brings the barrel's overall length to the 16" nominal regulation. Some do not like the fixed flash hider as it limits the ability to remove the FSB for some upgrades. Others don't care, happy to have a shorter barrel without NFA stigma.

AR-15 (or simply AR) is now the generic term for everything from an M4 to a Mk12. The original AR-15 was a select-fire rifle for military consideration. It has, however turned into the category of all Stoner AR-15 based direct-impingement firearms. Actual military designations have little to do with commercial designations, as they are free to call whatever they make whatever they want, despite existing names.

[rmecapn]

M16A1- Product improved M16. Changes- Forward assist, case deflector; bird-cage flash hider

Just nit-picking, but the case deflector was not a part of the A1 mods, it came with the A2.

[Dastook]

Great info guys. I'm getting an education. Thanks

[Failure2Stop]

Just nit-picking, but the case deflector was not a part of the A1 mods, it came with the A2.

Thanks for catching that. Failure to proof-read is a mo-fo.
Editing post to reflect correct info.

[rmecapn]

You know what's really interesting in the military modification area? I have pictures from an article in a 1968 issue of Popular Mechanics that shows the M16 with ribbed tubular handguards. (And I'm pretty sure it's a M16 not a M16A1.) Those were never issued and I wonder who finally decided they were a better design and put them on the M16A2.

[lowprone]

Blake Stevens, Ed Ezell book The Black Rifle