It was my understanding that the M4 has a 14.5" barrel, period.  However, I see many adds and references to 16" M4 barrels.

Now, I know that we tend to use terms interchangeably from time to time, which is fine.  But, from a purely technical perspective, I like to have my shit in order.

So, when one refers to the M4 barrel, should we always be talking about 14.5", 1/7, chrome, 4150, m230 cutouts, and feedramps?

Or does the "M4 barrel" really refer to the m203 cutout profile in the vernacular?

Or do I worry too much?

The art of a launguage of science is in the details.

M4 = Colt 14.5 1/7 chrome lined m203 step down.

M4 = a2 upper + safe/semi/burst
M4A1 = flat top upper +
safe/semi/auto

Remember! [:)]  M4 is Colt, but I will get [flame] for this last comment.


Also I would like to add that the [b]UPPER[/b] is what is marked [b]M4[/b]. Not the [b]BARREL[/b].

I have a M4gery with a 19" M4 barrel.

Isn't the A2 upper (carry handle, 20" bbl) with burst an M16A3?  The M4 designation refers to a flattop, doesn't it?

In general, at least on this board, the primary characteristic of an M4 or M4-type barrel is the cutout profile, and usually light profile under the handguards.  That's why people refer to an 14.5" or a 16" M4 barrel.  The twist could also vary:  1/7 or 1/9.  Then there's chrome lined and non-chrome lined.

The true military M4 is 14.5" chrome-lined with 1/7 twist.

Here ya go!

[url]http://www.autoweapons.com/photosv/m16m4a2up.html[/url]

[url]http://www.specialoperations.com/Weapons/Features/M4/Page_Two.htm[/url]

Yep, especially since for the majority of us, the closest we can come to the correct barrel length is 14.5" with a 1.5" flash suppressor.  

This is what I call my "M4gery", but it's not very close to a real one.  

[img]http://photos.ar15.com/WS_Content/ImageGallery/Attachments/DownloadAttach.asp?sAccountUnq=2207&iGalleryUnq=777&iImageUnq=18698[/img]

About the only thing that's "M4" about it is the barrel profile.

Asked a class3 dealer if he ever saw a REAL M4 and he said yep.....for over $10,000.

I would believe the price but the former?  Probably BS!

The M4 carbine also has a flat top, it is not only the M4A1.



I believe that the M16 versions go like this:
M16- Air Force version of the M16A1 except that it lacks the forward assist.
M16A1- forward assist with semi/auto selector
M16A2- fixed carry handle with semi/burst selector
M16A3- M16A2 except with flat top and semi/auto selector instead of semi/burst
M16A4- M16A2 with flat top

"The M4 carbine also has a flat top, it is not only the M4A1."


From the link I posted above.
"The M-4 & M-4A1 are capable of taking a wide array of accessories, one of the more common of these is the use of a removable carrying handle found on the M-4A1 Carbine.  The use of this "flat top" allows it to mount a number of optical sights depending on the role needed, including both day and night sights (see Figure 3-1)."

Okay, I thought it was:
M16 - 3-prong flash hider, no forward assist.
M16A1 - birdcage flash hider, forward assist.
M16A2 - fixed handle, improved sights, semi-full auto.
M16A3 - fixed handle, A2 sights, semi-burst
M16A4 - flattop, semi-full auto.

I could be way off on this, but that's what I thought. (And we've done quite a job of hijacking this thread now!)

I think the confusion comes from the multiple meanings of M4.  ARFCOMers are pretty certain we don't mean the WW2 Sherman tank or the 12v Surefire light.  IMHO, there are three different "M4s": the M4 barrel profile, the M4 carbine specification, and the M4geries.  

The "M4 Barrel" would be the barrel on the M4 Carbine: 14.5", chrome lined, ~.61" under the handguards, A2-style flashhider.  I think it's okay to say 16" M4 barrel and mean a part identical except in length, and say 16" 1/9 twist M4 barrel when it has a different twist, because we can assume all other traits are the same.  To be more specific, we should likely say "M4 Profile", but it's a little redundant.

Spooge:  I think all but a few of the first M4-nothings were flattop.  

Horik: I agree with you.  A real M4, stamped "M4" would be manufactured after the 88 MG ban, and should be around $600-800 as a post-88 dealer sample.  
There may have been a few M727 "M16A2 Carbines" before 88, but I don't think they had the stepped barrel or were marked "M4 Carbine".
However, since there are M16A1 and A2 rifles updated to the M4 spec, I think a real M16 with a real Colt M4 upper would qualify as a "real" M4, and likely sell for $10k.  Just my $.02

eswanson:

I think you've got it mostly right, save for the last three:
A2 = carry handle, safe-semi-burst
A3 = carry handle, safe-semi-full
A4 = flattop, safe-semi-burt

These two things come up so often we need a sticky.  I've saved some of the previous threads on this.

There were 500 non feed ramp M4s purchased by the military during Desert Storm.


M4 DOES NOT NECESSARILY = COLT

"Spooge: I think all but a few of the first M4-nothings were flattop."

Read this and tell me what you think.

[url]http://www.impactsites2000.com/site3/data/TM9-1005-319-10.pdf[/url]

HAHAHAHAHA
I too am the kind of person who likes to refer to items by their specific designator.
How about this Most people refer to their M4 as an M4gery on this board. But If I recall correctly didnt the Navy (SEALS) recently Purchase several Hundred(or more) 16" barreled Armalites with the Mid-length Gas system, I believe they are calling them their "Recon Carbine" Sounds like a good name for all the M4gerys out there.
hahahahahahaha
cp  

I thought the whole 3-shot-burst thing was a failure; why would they go back to it for the A4?  

eswanson:
I'm not sure why.  I think the A4 is the A4 because it was released after the A3, not because it's better in any way.

Spooge5150:
What page were you referencing specifically?  

Why do  you say the 3 round burst was a failure?

The second one from the top is my M4.  it is a Bushmaster and I call it whatever I want because its mine.. [sniper]

[img]http://www.imagestation.com/picture/sraid59/p56c34eb0fc544a6b2f232c7ffb885168/fc5cdae9.jpg[/img]

I think that there's nothing in that manual that contradicts what Spooge said.  The M4 and M4A1 are both flat-tops by definition, but there were some early M4s that used an A2 fixed carry handle upper.  There's been some pictures come back from the sandbox of guys carrying M4-barreled carbines that have slick slide M16 uppers.

Well I have done a lot of research on the web, and have found that I am in error.
Early M4's had A2 style uppers but not all.
So I stand corrected.
M4 A2/A3 Upper with safe/semi/burst
M4A1 A3 Upper with safe/semi/auto.

Thank you all for driving me to get the right info!

Spooge humbled.

A couple of notes from "The complete AR-15/M16 Sourcebook" Second Edition

First there was the Abu Dhabi Carbine which had the 14.5 barrel with M203 cut outs.

Then there was the XM4 that was tested by the marines.
Then there was the M16A2 Carbine that the Army tested (Model 720)

Then there was the M4 (Model 723) which had A1 sights

Then there was the M4A1 with A2 sights

The book does not mention the M4 with flattop although is shows several images of the flat top version with the caption of just "M4"

now, where does the Model 727 which I heard a "operator" talk about on the Discover Channel fall into in this puzzle?

I don't know... makes ya nuts [banghead]

[url]www.isayeret.com[/url] has a lot of info on the fixed loop M4s.

I think the 727 model had A1 rear sight and the abu dhabi carbine as previously mentioned I beleive is what turned into the M4 but dont forget 14.5 inch barrels were in use way before even the A2 variant rifle or carbine on the A1 653 carbine basicaly an A1 version of a later M4.I have pictures of seals with hybrid rifles M4 fixed handle uppers and A1 lowers and the first batch of M4s were bushmaster made back in 90.Just the other dat in USA todat showed a SGT who was the winner of the silver star he had an M4 fixed A2 handle with the old slimmer handguards.To my understanding a plain M4 has always been a fixed handle burst model no feed ramps.

I have shot a M16A2 and it was semi/auto

Colt has designated their title I 16" civilian carbine as an "M4 carbine", so a 14.5" barrel isn't necessarily a prerequisite to be considered an "M4".

I have one of these. A1 sights rear, A2 sights front. Stamped "C MP 5.56 NATO 1/7"

By military designation the M16A2 is semi/burst with a fixed carry handle.  Colt has four versions of the M16A2 available for sale.  Model RO701: Semi/Auto with fixed carry handle; Model RO705: Semi/Burst with fixed carry handle; Model RO901: Semi/Auto with flat top upper; Model RO905: Semi/Burst with flat top upper.  Now Colt has redesignated the M16A2 models as M16A4, just like they changed the Commando to the M4 Commando.

Is there any chance we can collect and compare sources and petition a mod to make a sticky topic?

A good reference on the Colt model numbers is:
http://www.biggerhammer.net/ar15/variants/

Also, there's a good chance of "more modern" A2 and M4 uppers on older recievers, which would cloud the picture.  I recall the USAF rebarreled some old GAU-5/As to 14.5" barrels, leaving the upper reciever with field sights and no forward assist.

Where are you seeing this? The M16A4 is different from the M16A2. The Commando series uses 11.5" barrels while the M4 does not. Colt can call their guns whatever they want but the M16/A1/A2/A3/A4 and M4/A1 are spec'd to have certain features by the military. Colt changing their internal designations doesn't change the military designations.

FWIW, Colt calls their FA guns "M16A2" even when the sights are A1, just like they call their flattops "A3" but it's the M16A4 that has the flattop. If there is a 14.5" barrel it's an "M16A2 Carbine" and if the barrel is 11" it's an "M16A2 Commando"

The difference between the M4 and M4A1 is in the lower. The XM4 had the fixed carry handle.

You'll see any combination of uppers barrels and lowers in the military depending on what unit you're looking at. Some units upgraded old guns with new parts, some units bought whole rifles, some bought new upper units. If you're seeing slick side (M16) uppers you're probably looking at USAF guys with GAU's.

This is the biggest problem with using military terminology when discussing parts. This problem was discussed at length at the Colt armorers class. Unfortunately it's have become the favored method of naming parts and we'll probably have to live with it.

A true "M4" barrel will have the "4" marked barrel extension, be made of 4150 CM, be fully chrome lined, chambered for 5.56 NATO, be a 1X7" twist, 14.5 in length in an A2 barrel contour with the cut out for the front bracket of the M203, have a forged "F" marked FSB, be proof load and magnetic particle tested tested and use the same front sight post as the M16A2.

Oh yeah, and it will be roll stamped IAW the barrel prints and since Colt is the only one making M4s that roll stamping will say

[center][b]C MP 5.56 NATO 1X7[/b][/center]


[last part]

"Oh yeah, and it will be roll stamped IAW the barrel prints and since Colt is the only one making M4s that roll stamping will say


C MP 5.56 NATO 1X7"

Thank you Tweak! I love you man! [kiss]

Correction they still remain the M16A2 but the title of the page is the M16A4.  In regards to the Commando has been renamed the [url=http://www.colt.com/mil/M16.asp]M4 Commando[/url].  Also I did say that Colt redesignated them, I never said that the military did.

Exactly. I have a registered M16 in transfer right now. When I take possession of it around the first of the year, I will be adding a 14.5" flattop M4 upper, Aimpoint M2, ARMS #40, ARMS #45 SIR, Vltor stock, Surefire 900A, and Gemtech M4-96D suppressor.

It will be selectfire (safe/semi/auto) and I will refer to it as an M4A1. [:D]

You can call it whatever you want but real M4s use lowers having the A2 reinforcements. Is your transferable an M16A2?

I remember seeing all the "Colt M4s" (semis) on gun show tables when the AWB was nigh. Lots of Colt M4 uppers (complete) mounted on any Colt lower the dirtbag could lay his hands on combined with whatever knock off no name stock he could scrounge. Those weren't M4s either but most of the chimps walking the aisles didn't know any better and paid a serious, and unwarranted, premium for a "Colt M4".

Mb121,

True, you never said the military changed the designation but to someone who doesn't know how the system works it could sound that way. Hence my statement.

"M4 Commando" makes sense as a Colt designation since it is not an M4 (tho it has most of the M4 features) and does have the Commando barrel. If it was an M4 Colt would call it an....M4, actually they would call it an RO727, 728, or 729. Even the civilian models say, "Ninja Law Enforcement Super Tactical M4" not simply M4.

Reminds me of my car, a Subaru Impreza Outback Sport. It's not an Outback body, it's an Impreza body but it has slightly higher ground clearance so that makes it "sport", dunno how the Outback fits into the name, maybe just marketing hype, maybe some hidden features like suspension. Care less about this discussion than that. [:D]

I'm not familiar with this - are you referring to the raised fence around the mag release?


.

The fence under the ejection port and around the mag catch button came in earlier. Some of the earliest AR15s (FA) had no fence at all.

[img]http://harrison.customer.netspace.net.au/m161.jpg[/img]

A picture is worth a thousand words.

[img]http://photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=16145[/img]

A1 on left

[img]http://photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=16146[/img]

A1 on top

[img]http://photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=16152[/img]

A1 on left