The Colt M4A1 SOCOM Barrel





A genuine Colt M4 SOCOM barrel is 14.5” long and has a medium contour underneath the handguards (not a heavy barrel profile).  The barrel has a NATO chamber and a 1:7” twist.  The SOCOM barrel has the typical M4 circumferential cut-out located approximately 1.4” forward of the gas block for the attachment of an M203, as well as rectangular shaped cut-outs underneath the handguards on the port and starboard sides of the barrel, located approximately 1.4” aft of the gas block, for the same reason.  The SOCOM barrel employs the carbine length gas system.











The barrel stamp located just aft of the flash suppressor reads:

            C   MP
5.56 NATO 1/7








The barrel has an “F” marked front sight base and a side sling swivel.  The “F” mark is located on the port side of the front sight base.











The SOCOM barrel will have a “date code” located immediately aft of the handguard retaining ring.  The handguard retaining ring itself will also have cut-outs located at 4:30 and 8:30; again for the attachment of an M203.








The barrel will also have a small “O” stamp, that is located at the chamber section of the barrel, indicating a chrome-lined chamber and bore.







Naturally, the SOCOM barrel will have M4 feedramps and there will be a numeral “4” stamped at the 3 o’clock position on the barrel extension.







Here are a couple pics comparing the SOCOM barrel to the standard M4 barrel.










Accuracy Evaluation



I performed an accuracy (technically precision) evaluation of the Colt SOCOM barrel following my usual protocols. All shooting was conducted from a concrete bench-rest from a distance of 100 yards (confirmed with a laser rangefinder.)  For the accuracy evaluation, the barrel was free-floated using a Daniel Defense Omega rail.  




This accuracy evaluation used statistically significant shot-group sizes and every single shot in a fired group was included in the measurements.  There was absolutely no use of any Group Reduction Techniques (e.g. fliers, target movement, Butterfly Shots).  

As many of the significant variables as was practicable were controlled for.  The free-float handguard of the carbine rested in a Sinclair Windage Benchrest, while the stock of the carbine rested in a Protektor bunny-ear rear bag.  Sighting was accomplished via a Leupold VARI-X III set at 25X magnification and adjusted to be parallax-free at 100 yards. Wind conditions on the shooting range were continuously monitored using a Wind Probe.  The set-up was very similar to that pictured below.





The Wind Probe.





Using match-grade hand-loads topped with Sierra 55 grain BlitzKings, I fired three 10-shot groups from the Colt SOCOM barrel in a slow, steady manner from 100 yards.  Those groups had extreme spreads of:

0.90”
1.02”
0.93”

for a 10-shot group average extreme spread of 0.95”.  All three of the 10-shot groups were over-layed on each other using RSI Shooting Lab to form a 30-shot composite group.  The mean radius for the composite group was 0.35”.

The smallest 10-shot group.





The 30-shot composite group.

Great work, Molon.

I assume GI barrel assemblies will include A2-style flash hiders; is this correct?  What model are the flash hiders on the barrels in your pictures?  Are they the same model?  The SOCOM's FH seems to have straight tines, while the M4's tines go counterclockwise.

You're correct.  My two barrels have permanently attached Vortex flash hiders to bring them to the legal length.  No SBRs allowed for the unwashed masses in my state.

Bingo!

Molon,

Just curious,  where dd you get the upper and who welded the Vortex?  

T

Ummm...Am I the only one who cannot see any pics?  

People looking to buy a SOCOM barrel need to be alert to the length.  There were alot of them sold last year that the factory threads had been cut off, shortening the barrel 5/8" to 3/4", and then new threads cut.  They had the step directly behind the threads recut but maybe some didn't.  They were reparked and often sold as new or new take-offs.  They may shoot fine but there is no reason to pay a premium for a cut down mis-represented barrel.

Stripped down, they look like this:

Excellent illustrative write-up Molon!  Of course, I already knew it all.  

Cheers

Would you mind weighing the stripped barrel and posting your results?

My apologies, Molon - that barrel was only in that state for about a week, and I didn't get a weight on it.  It's completely built now, with a pinned Phantom on it.  Sorry, man...  

Thanks for the write-up.
My Socom barrel has the exact same markings, made in 04/04.
The gun on the left is the one with that barrel. Colt M16A1, DD Omega, Magpul parts. I have replaced the FCG with Geissele parts, and it has an MGI buffer with Wolff extra power recoil spring.

Who's receiving the M4's with SOCOM barrels?

Thanks for posting this article, and great work on the pictures. I got tired of looking at all that barrel sticking out on my Colt 6721 so I sent it to ADCO for a chop job - from 17.5" (w/FH) to 16.10" w/FH pinned. At the same time I have a middie/med-con upper being made at CMMG for another carbine. Having the Colt HBAR now with a more 'correct' barrel length, I doubt if I will build another carbine, but the SOCOM barrel sure looks good. I guess the 'medium-contour' CMMG barels are about the closest to it, at least under the guards - except for the mounting cuts, of course.

I've never seen that Young flash hider.  How does it compare to the Smith Vortex?  Sorry to go off topic.

I am a big SOCOM fan and would love to see these pics, but I am getting nothing. I am not even getting any red X's . Molon, did you remove the pics from the writeup?

Thanks!

My M4 Match Target has all of that except for the Medium Profiled barrel.-
Steve

They're all showing up on my screen.   Try hitting your refresh button.

I'm seeing the pictures with no problems.

This is VERY weird. I cannot get them to show up no matter what I do. It's like they were never even posted, just text. ??

ETA: I can see everyone's pics except Molon's. Never had this happen before.

The FH isn't a straight A2 model.  There is a notch (@6 o'clock if I remember correctly) for mounting the issued suppressor.  Special Forces Groups are issued the SOCOM barrels but only at ODA level.  HHC's and Group Support Battalion have the standard M4A1.

CD

A far as I know Colt and CMMG both stopped making this barrel. I think Socom stopped asking for it and decided to use a standard M4 barrel to save weight.

Do you see other people's Photobucket pictures?  Could your ISP be blocking Photobucket?

I see everyone else's pictures, just not Molon's.

It sounds like you are referring to the Knight's M4QD mount which is associated with the QDSS-NT4 suppressor.

Cheers

I haven't done any formal testing comparing the two.

Good write up and excellent quality pics. It is nice to read posts, written by someone who can write well.

I will post a pic just for giggles.
FYI, in reference to Colt M203's, they are not all the same. I found this out the hard way when I had to assemble a bunch of them on M4A1s that were meant for fixed carry handle systems. It took a lot of sweat, cussing and some slight mods to get them right.

Slight mods?  Can you elaborate?

There is a recent article about the Army probably going to the SOCOM barrel for all M4s.

wow... thx for posting that

Can we get a barrel diameter measurement of the two barrels just aft (to the barrel nut side) of the rectangular SOCOM cut?  Thanks.

This is the why of the SOCOM.

The SOCOM barrel has a diameter of approximately 0.850" at that point.  I don't currently have a standard M4 barrel on hand, so maybe someone else can provide the comparative measurement.

M4A1 + SOCOM = SAW !!   Well just about anyway.  Got two of these beasties on a pair of M4's and one M4 with the std. Govt. bbl.  The weight
difference is noticeable, but certainly not excessive.  I like 'em !

I'm not particularly a fan of the two piece design free-float railed handguards.  However, I have to say that the Daniel Defense Omega Rail is a very nice option for those who choose to go that route.  My M4 SOCOM upper will be wearing one during its accuracy evaluation.

I've not heard any indication that Colt has stopped production of 921HB barrel, if anything they seem poised to ramp up production pursuant to the possibility of going to a MEDCON barrel for all RO920 and RO921s (USGI M4 and M4A1 Carbines).

Also, there's a rumor out that BCM is going to be producing M4A1 profile barrels in the near future as well which could make high quality barrels available for more reasonable prices than the somewhat relatively rarer Colt barrels.  

~Augee

This is the Internet.  If someone posted it, it must be true.

This kinda makes you wonder a bit...IF the SOCOM med. weight barrel  makes a big difference on the M4A1 with full auto, then what would be the
result of using a 6721LE barrel on the same weapon??  Now that would raise the weight a bit, but you'd never have to worry about frying the
barrel.  The 1/9 twist would also be slightly beneficial in F/A, as it would generate a bit less heat.   It will, of course never happen, but just a
thought.

Accuracy evaluation added to first post.

My M4 with SOCOM bbl.

Has molon tested a standard m4 barrel with the same rounds? I have suspected these barrels are not worth it for semi auto

I have a CMMG socom its great but my Colt socom seems to be a bit thicker dimensionally than the CMMG.BCM alreDY HAS THE SOCOM AVAILABLE FOR $259 BUT YOU HAVE TO SEND TO adco TO HAVE AN fsb INSTALLED..sorry for the caps..wich still makes it a $400 barrel..ive seen and got my Colt socom brand new never mounted for $375 on the EE.Nothing against BCM I have one of their barrels but if I casn get an original Colt for the same money or just a bit less ill go that route.

I dont see the point of them unless your putting out alot of full auto fire.

Is that a QRP mount for the Aimpoint?

If so did you use the spacer?

With the spacer will it give center cowitt?

What I wonder?

With doing several mag dumps wont the GAS TUBE Fail before the Socom barrel or even the M4 barrel


When I saw the COLT video on the reg. M4.   I would of liked to seen the gas tube? I bet it was cooked just like the M4 barrel

Oh boy, another old topic from the past!!

Thanks for adding to this discussion.

The advantage is heavy barrels take the heat better..id rather have the heavier more heat resistant barrel that will boost rate of fire because heat is handles better.There very relevant for semi auto use especially if sustained fire was needed..what if the weapon was ever needed to fight with and had to be used that way I would rather have the uneeded all the time advantage for 6 ounces more than regular M4 profile than need it and it not be there.Weight increase is slightly noticed and it balances better.Ill bet you would see HBARs in use it wasnt that the M203 in american use was attached to the barrel.If we used a QD m203 that ran off the rail system you would see un M4 notched medium weight barrels id bet on the M4.