Differences between CAR-15 and M4?


July 24, 2003, 02:12 AM
What are the Differences between CAR-15 and M4?

If you enjoyed reading about "Differences between CAR-15 and M4?" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!
July 24, 2003, 04:07 PM
.... and, are their uppers interchangeable with an AR-15's ?

July 24, 2003, 04:38 PM
well the real deal are
semi and full auto for the CAR15
and Semi and Burst for the M-4
The M4 has a flattop
the M4 has feed ramps milled into the upper receiver

Bartholomew Roberts
July 24, 2003, 05:26 PM
Well strictly speaking, theonly model ever officially referred to as a CAR-15 is extremely rare. It has short triangular foreguards, a 10.5" barrel, a shortened retractable stock that looks like a regular M16A1 stock but has a switch on the butt for collapsing/extending it. Here is an Airsoft copy:


Since then, people have taken to calling any shortened AR15 series rifle a CAR-15 and there are a bunch of different variations.

The M4 is an official military designation (M1 Carbine, M2 Carbine, M3 Grease Gun and now... the M4). It has a 14.5" heavier barrel with a step for M203 mounting. It has more oval shaped handguards with double heat shields to protect from the increased heat of the shorter barrel, although most are outfitted with RIS/RAS rail systems now. Rear sights are marked 6/3 vice 8/3. The front sight is 0.40" taller and narrower to give the same sight picture as a 20" with the shorter sight radius. Early ones have an A2 style carry handle but current production is all flattop. M4s are burst-only. M4A1s are full-auto.


July 24, 2003, 05:39 PM
Yeah, original specifications for M4s did not mandate flat-tops, It just evolved very quickly due to obvious benefits.

July 24, 2003, 06:00 PM
The original was the CAR-15 "Commando" with the 10" barrel, a 3-prong flash suppressor, collapsible stock and triangular handguards.

The Air Force wanted one, so they created the CAR-15 "Survival Rifle" which retained the 10" barrel, a shorter pistol grip, a cone shaped flash suppressor, a fixed, tubular buttstock and rounded handguards. Due to the huge fireballl when fired, the Air Force decided not to adopt them.

Colt then created the XM177 which had a 4.5" flash suppressor (which ATF decided was also a sound suppressor), 10" barrel, collapsible, tubular buttstock and no bayonet lug.

When the forward assist was added to the M16, it was also added to the XM177, which was then designated the XM177E1.

About a year later, the barrel was lengthen to 11.5" and it became the XM177E2. It remained in this configuration until it was replaced in the 80s with the M4.

July 24, 2003, 07:32 PM
Is the Colt civilian M4 mil-spec (not counting the burst-fire)? Are there any differences in the Colt M4 and the Bushmaster M4 (civilian models)?


July 24, 2003, 10:08 PM
The colt lower has diferent diameter parts and I had abuddy who got one new out of the box and the buffer was plastic,Ihave bushmaster and RRA and they are way better than the colt closer to the mil spec.

July 25, 2003, 03:57 AM
The Colt has a metal buffer or at least my M-4/6400c does. Sure looks and feels like metal as I type this. The only "plastic" part is the nylon end on the buffer.

Pins are indeed bigger diameter, I measured them just now. But, unless you want to drop in the full-auto parts who cares?
I like the pins bigger; maybe a hair bit sturdier that way?:scrutiny:

Here's what is not "mil-spec" in all 3: Bolt Carrier, Safety/Selector Switch and Trigger Group.
That's what's listed as different from "mil-spec" in Bushmasters catalog.
If you do have these true "mil-spec" parts in your AR it's now considered an M-16 by the ATF.

From what I can see my Colt has a barrel marked C MP , 5.56NATO 1/7. The handguards are the newer oval like the military M-4's, side mounted slige swivel like the military M-4's, flat-top reciever w/removable handle-sight assembly like the newer miltary M-4's and a fixed stock that looks alot like an M-4's telescoping stock. Even has the step in the barrel for the M-203 to mount there too bad it ain't an option.:D

July 25, 2003, 07:49 AM
Ahem. According to "The Black Rifle," IIRC, "CAR" only means "Colt Automatic Rifle" and can be applied to any M16. The shorty was called the Commando, IIRC.

July 25, 2003, 09:47 AM
Even has the step in the barrel for the M-203 to mount there too bad it ain't an option.

Ah, but it is. If NFA weapons are legal in your state, you can buy one. If not, you can add a 37mm "flare" launcher to your M4gery. Another interesting option is a 12 gauge pump shotgun that mounts on the bayonet lug, and uses the magazine as the pistol grip like the grenade launcher.

July 25, 2003, 12:15 PM
My concern is, if I needed to replace any trigger/fire-control parts in the Colt, would I have to go to Colt for them or would parts from Bushmaster, etc. work? If the pin diameters are different, it sounds like it would be a problem. I also read somewhere that Colt puts some kind of steel block or blocks somewhere in the fire control components to prevent full-auto modification. If that's the case, do these block non-Colt replacement parts from being used, such as Bushmaster, etc.?


July 25, 2003, 12:55 PM
The block makes working on the fire control group a little harder and I think it has to be modified or removed for a 2 stage set trigger,Bushmaster does have the larger diameter parts for at least the last 5 years when I had the colt at the time you couldnt get parts for the late model except from colt and that was a nightmare dealing with them.To big g the first colt car 15 was a short barrel short triangular hand gaurd and telescopic stock that looked like a full size stock at half the legnth and was called the car 15 and it does stand for colt automatic rifle,then before the commando iw was the XM177E1 and E2 with forward assist,the commando 11.5 barrel with bird cage flash hider was out I beleive the same time as the 653 carbine wich eventualy evolved into the M4,the 653 was the first to have the 14.5 barrel.

July 25, 2003, 01:36 PM
Thanks, BDM. I have a suspicion that people mistake CAR for CARbine rather than Colt Automatic Rifle.

July 25, 2003, 01:45 PM
I still call mine a car15 and some times "shorty"it depends on how you feel,ive talked to guys who used it and called it by diferent names that I cant list because I like this site and dont want to get booted,I remember reading I dont know where and the article was"the car-15,sworn by and sworn at"but car is probably used more for the shortest of them,the ones used as sub guns,its like if you have ever seen platoon the carbines carried by sgt barnes and alias have 16" barrels a legnth not used by the military at that time it was either10.5,11.5 and had the big supressor or sometimes the 3 prong the case with the first car15,Ther is a book put out by the navy seal museum called special warfare special weapons youll love it shows evry variant of rifle,pistol sub gun,knives grenades evry thing the udts and seals ever used.:D

July 25, 2003, 01:58 PM
This might help....although I think I'm more confused than I was before. lol

CAR Overview (http://www.isayeret.com/weapons/assault/car15/car15.htm)

M4 Overview (http://www.isayeret.com/weapons/assault/m4/m4-alone.htm)

July 29, 2003, 03:07 PM
The M-3 carbine is simply an M-2 Carbine with the infra red night sight.

The submachinegun family folowed it's own protocol-M-1 was the simplified Thompson, the M-2 was a little seen GM product, the M-3 was the Greasegun.

July 29, 2003, 03:23 PM
"Is the Colt civilian M4 mil-spec (not counting the burst-fire)? Are there any differences in the Colt M4 and the Bushmaster M4 (civilian models)?"

The Bushmaster doesn't have the feed ramps milled into the upper receiver, the Bushmaster doesn't come with the double heat shielded handguards, and the Bushmaster has a different muzzle brake called a mini-y-comp.

I personally own the Bushmaster. It is a great rifle and IMO gives up very little to the Colt for less money. The handguards are no big deal, for one thing, I don't allow my carbine to get that hot, for another thing, I bought a set of real M4 handguards to put on it for the look. I also intend to replace the handguards altogether when I install a KAC RAS II, but this won't happen until I finish a half dozen other AR15 projects. The feed ramps are nice, but I have never had a feeding problem with any of my AR15s and none have the feed ramps. The one thing that I don't like is the muzzle brake. It is very loud, but in truth I just would prefer to have the look of the real thing. I am going to send my M4 to KKF and have a clone muzzle brake installed. I personally would rather own a Bushmaster than a Colt, although I own both in addition to Cav Arms, Oly (SGW), and Mega Machine.

I am not sure what the situation is with the pins. Some Colts have large pins and some don't. I am not sure about the M4. You can use the lower with any of the many different AR15 uppers regardless of pin size by using an adapter. This is not as convienient IMO, but it will work fine.

July 29, 2003, 04:32 PM

July 29, 2003, 06:13 PM
On the CAR thing...Jim Sullivan said in an interview that the "AR" stood for the first two letters of the manufacturer, "ARmalite" and I'd always understood the 'C' in "CAR" stood for "Commando" as Hkmp5sd said. Add to this the fact that there are other "AR"s (eg AR7) that are not automatic and you have a bit of a dilemma.

What's the consensus on the true meaning of the 'C' (or "AR" for that matter)?

July 30, 2003, 11:34 AM
According to "The Black Rifle," which is supposed to be the definitive source, Colt Automatic Rifle. Now, you can call it whatever you want, and most people do. :neener:

As BDM mentioned, the actual Army nomenclature was sumpin like XM177xx so CAR was Colt's designation, just like AR15 was. The govt nomenclature of the rifle has never been AR15; it is M16xx. My GI M16 was stamped Colt AR15 Model M16, if my rapidly fading memory serves me.

July 30, 2003, 02:05 PM
The govt nomenclature of the rifle has never been AR15; it is M16xx. My GI M16 was stamped Colt AR15 Model M16, if my rapidly fading memory serves me.

And the civilian one in my safe is stamped Colt M16A1. :neener: Gotta love the gov'ment.

If you enjoyed reading about "Differences between CAR-15 and M4?" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!