Colt M4A1 SOCOM Barrel Accuracy: Another Look

[Molon]

Colt M4A1 SOCOM Barrel Accuracy: Another Look

In 2010, I posted one of the first publicly available, in-depth accuracy evaluations of a Colt M4A1 SOCOM barrel. At that time, the Colt SOCOM barrel was relatively new to the civilian market. Many people, including myself, were pleasantly surprised by the level of accuracy/precision that I obtained with the SOCOM barrel; particularly since it is a chrome-lined, NATO chambered “military-grade” barrel. Since that time, the Colt M4A1 SOCOM barrel has developed a significant appreciation amongst AR-15 enthusiasts.


The M4A1 SOCOM barrel

Recently, I assembled another upper receiver group based on the Colt M4A1 SOCOM barrel. This new build features a Colt cage-code marked M4 upper receiver, a Colt “C” marked bolt carrier group and a 13” Geissele MK14 M-LOK free-float hand-guard.

A genuine Colt M4A1 SOCOM barrel is 14.5” long and has a medium contour; it is not an HBAR. The barrel has a 5.56mm NATO chamber and a 1:7” twist.

Colt SOCOM barrel

Colt HBAR

A genuine 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 hand-guards on the port and starboard sides of the barrel, located approximately 1.4” aft of the gas block, for the same reason. The gas port on a genuine SOCOM barrel has a diameter of 0.062” and the barrel employs a carbine-length gas system.


The SOCOM barrel has a stripped weight of 1 pound, 14 ounces. That is only 2 ounces heavier than the ubiquitous 16” government profile barrel found on the Colt 6920.

Colt SOCOM barrel

Colt 6920 barrel

The stripped weight of the SOCOM barrel is 5 ounces heavier than the stripped weight of the standard Colt 14.5” M4 barrel. The pic below shows the difference between the standard M4 barrel and the SOCOM barrel. From the gas block journal forward, the two barrels are identical


SOCOM barrel on top, standard barrel on bottom

The next pic is a close-up comparing the two barrels in the area between the chamber and the gas block journal, showing you were the extra weight is added.

The date-code on my original SOCOM barrel was “11/03” and the date-code on my newer SOCOM barrel is “02/18”

My original SOCOM barrel hand an “F-marked” front sight base. Colt no longer stamps an “F” on their front sight bases, but their newer front sight bases maintain the length of 1.98” from the top of the barrel to the shelf for the front sight post.

My original SOCOM barrel was stamped:

“C MP 5.56 NATO 1/7”

The newer SOCOM barrel is stamped with Colt’s cage code.

“13629 M P 5.56 NATO 1/7”

Both of these SOCOM barrels have the “O” stamp near the chamber portion of the barrel, indicating the barrel has a chrome-lined chamber and bore. Naturally, the M4A1 SOCOM barrel has M4 feed ramps.

Accuracy Is Final


In 2010, my original SOCOM barrel with the “11/03” date-code produced a 10-shot group fired from a distance of 100 yards that had an extreme spread of 0.90”. That group was fired from my bench-rest set-up using match-grade hand-loads and a high magnification scope.

My newer SOCOM barrel with the “02/18” date-code produced a 10-shot group fired from a distance of 100 yards that had an extreme spread of 0.93”. This group was fired off of sand-bags using match-grade hand-loads and a high magnification scope.

. . . .

As a side note, the pic below shows what a great job Ken Elmore of Specialized Armament does on his pin and weld jobs.

.......

 

[R. Moran]

So, this is interesting to me.

We recently received rebuild/converted M4A1s....and we are having a hell of time getting them zero'd at 25 mtrs. They seem to wonder as they heat up, leading us to chase the group, or shoot a few 3rd groups before we actually make sigh adjustments...iron sights w/ the matech rear.

I've tried to consider and isolate variables best I can on a range where everyone just wants to shoot the minimum and go home. I will say I/we did not not see this with old A2 that were previously issued, and some still are.

Additionally I had an upper built with a socom barrel that I shot in a Shrek class, years prior. I had a hell of a time zeroing it, same issues...but with a FF handguard and optic....for the course I was able to shoot it well enough though. I eventually traded the barrel for a Noveske N4 barrel...and the gun had no further issues.

Next qual we should have a mix of optics, hopefully that will eliminate iron sights as a variable, otherwise I'm at a loss.

Any ideas?

 

[Stjjames]

Nicely!
A buddy built a carbine- with the same barrel.

 

[UtahLeftyGunner]

Molon, I’ve always appreciated your write ups. Your original socom post led me to acquiring one in 2013 and I have not been disappointed.

 

[Carlos0311B]

So, this is interesting to me.

We recently received rebuild/converted M4A1s....and we are having a hell of time getting them zero'd at 25 mtrs. They seem to wonder as they heat up, leading us to chase the group, or shoot a few 3rd groups before we actually make sigh adjustments...iron sights w/ the matech rear.

I've tried to consider and isolate variables best I can on a range where everyone just wants to shoot the minimum and go home. I will say I/we did not not see this with old A2 that were previously issued, and some still are.

Additionally I had an upper built with a socom barrel that I shot in a Shrek class, years prior. I had a hell of a time zeroing it, same issues...but with a FF handguard and optic....for the course I was able to shoot it well enough though. I eventually traded the barrel for a Noveske N4 barrel...and the gun had no further issues.

Next qual we should have a mix of optics, hopefully that will eliminate iron sights as a variable, otherwise I'm at a loss.

Any ideas?

We saw “sights” issues with iron sights 2-3 years ago. If the rifle had issues, 90% of the time it was because we had to go 20-25+ clicks left or right to achieve zeros. After I shot 3-4 rifles to confirm it wasn’t the shooter, we started putting MG targets behind the zero targets to catch the impacts. I wish the army did what the marines do. Have an armorer on the range with spare parts, gauges and tools to help on the range. The armorers used to move the front sight if our zero was more than 15 clicks left or right.