Armalite Mid-Length Carbine and A.R.M.S. Mid-Length S.I.R. System.

Print Friendly, PDF & Email

by David Crane

Included in Gary Paul Johnston’s October 2003 "Soldier of Fortune" article is some great info on both the Armalite Mid-Length Carbine and A.R.M.S. Mid-Length S.I.R. System.

The Armalite Mid-Length Carbine was designed specifically to overcome the long-known gas system-related problems associated with the standard M4/M4A1, problems that have been plaguing end-users for years. These include greatly accelerated gas port erosion, , excess heat, higher operating gas pressures, melted and blown-out gas rings, and an open/iron sight radius that’s too short. None of these are good things on a field combat weapon.

So, how does the the Mid-Length Carbine mitigate these problems? The Mid-Length Carbine moves…

the front sight base/gas block 2 inches forward from its position on the M4/M4A1 Carbine. This puts the Armalite Mid-Length Carbine’s gas port mid-length between that of the M4/M4A1 carbine and full-length AR-15/M16 rifle, thus the Mid-Length Carbine’s name.

The 20-inch barrelled AR-15/M16’s gas port is located 12.5" forward of the chamber and 7.5" back from the muzzle. The M4/M4A1 Carbine’s gas port sits 7.5" in front of the chamber and 8.5" back from the muzzle. The Armalite Mid-Length Carbine places its gas port 9.5" in front of the chamber and 6.5" behind the muzzle.

All this serves to put the Armalite Mid-Length Carbine’s gas port closer to the full-length AR-15/M16’s optimum operating pressure curve allowed by its 20" barrel. This results in less gas port erosion, reduced heat, slower bolt velocity, improved extraction, and a longer sight radius.

Armalite is now introducing a semi-auto version of the Mid-Length Carbine called the Special Operations Forces (SOF) Carbine. This is a post-ban gun that features a fixed-position telescoping/retractable-style stock, M4-style 16" barrel w/muzzle brake. The Armalite SOF Carbine will be available in both A2 and A4 configurations. Armalite also has AR-10 versions in 7.62x51mm/.308 caliber.

According to reports, the Armalite Mid-Length Carbine is 100% mil-spec. Also, the feed ramps of the barrel extension extend down into the mag well for greater feed reliability under adverse conditions. This should greatly reduce the risk of nose dives.
As if all this isn’t news enough, there’s a new mil-spec A.R.M.S. Mid-Length S.I.R. System designed to perfectly complement the Armalite Mid-Length Carbine and SOF Carbine. The new A.R.M.S. Mid-Length S.I.R. System apparently mates perfectly to the Mid-Length Carbine(and SOF Carbine) upper receiver, since both components are mil-spec.

While preparing his article on the Armalite Mid-Length Carbine and A.R.M.S. Mid-Length S.I.R. for the October 2003 issue of "Soldier of Fortune(SOF)", Gary Paul Johnston mounted an EOTech 552 Holosight (Holographic Diffraction Sight) onto the A.R.M.S. Mid-Length S.I.R. System, and he attached an NSW Crane/SOPMOD retractable/telescoping buttstock onto the buffer tube of one of his pre-ban semi-auto lower receivers, so he could run some drills with the Armalite Mid-Length Carbine upper/A.R.M.S. Mid-Length S.I.R. System combo. Gary used Redi-Mags(for faster reloads) equipped with Magpul magazine protectors. His personal AR-15/M16 rifles are all equipped with the new and improved ERGO Grip from Falcon Industries.

By the way, Gary’s choice to use an EOTech 552 Holosight/Holographic Diffraction Sight was an excellent one. The only other optical gunsight I would currently put in the same class as the EOTech 552 is the Aimpoint CompM2 red-dot optical gunsight. The differences between the two are several. The EOTech 552 is a Heads-Up Display (HUD)-style sight that utilizes a true holographically-projected reticle. The most common style of reticle for the EOTech is a circle-dot, although a plain dot option is also available.

The Aimpoint CompM2 is a red-dot tube sight. The EOTech allows for slightly faster engagement of multiple targets in CQB environments, but the Aimpoint CompM2 red-dot is plenty fast. The EOTech 552 also gives the operator a less-obstructed field of vision than the Aimpoint provides, since the EOTech is a heads-up display (HUD) as opposed to a tube sight. The Aimpoint CompM2 is water-proofed to a greater depth, and has a proprietary battery/power system that lasts much longer than the EOTech’s power unit.

According to reports DefRev has received, the Aimpoint CompM2 may also be slightly more durable than the EOTech 552, but that remains to be proven. The EOTech is plenty durable. In fact, the EOTech remains functional even after most of the site has been obstructed by particulate matter or even destroyed. Its holographic projection/display technology is what allows for this.

The EOTech 552 and Aimpoint CompM2 are, in my opinion, currently the two best optical sights in the world for CQB and perimeter security, due to the superior multiple target engagement speed that they allow, their ruggedness/durability, and their overall quality of manufacture. At extended ranges, the Trijicon ACOG sights start coming into their own, due to their magnification aspect.

If you’re military or law enforcement, you can inquire about the Armalite Mid-Length Carbine by calling Charles Topp at 502-532-0300 or contacting him via email at Civilians who want to find out more about the Special Operations Forces (SOF) Carbine can contact Armalite at 1-800-336-0184 or via email at To visit Armalite’s website, click here.

If you’d like to find out more about the A.R.M.S. Mid-Length S.I.R. System, you can contact Atlantic Research Marketing Systems, Inc. (A.R.M.S.) by phone at 508-584-7816, or via email at You can also visit their website at

DefRev recommends you visit the official "Soldier of Fortune" website and subscribe to that excellent publication. Those guys do good work over there. If you like tactical weaponry and accessories, you’ll definitely want to keep an eye out for Gary Paul Johnston’s articles. Gary is always one of the first guys to get to test the latest and greatest tactical toys.

Armalite Mid-Length Carbine and A.R.M.S. Mid-Length S.I.R. System. by

About David Crane

David Crane started publishing online in 2001. Since that time, governments, military organizations, Special Operators (i.e. professional trigger pullers), agencies, and civilian tactical shooters the world over have come to depend on Defense Review as the authoritative source of news and information on "the latest and greatest" in the field of military defense and tactical technology and hardware, including tactical firearms, ammunition, equipment, gear, and training.

Check Also

Ryker Grip: A ‘Patent-Pending, Biomechanically Optimized Shooting Method’ for Your Tactical AR-15 or AK Carbine/SBR

By Toby Melville March 25, 2024 From time to time, an individual assesses the status …