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Understanding AR Systems

Every few years or so a gun manufacturer develops a new operating system for the AR/M4. Here’s a look at the benefits and deficits of some of the most popular designs.

January 25, 2012  |  by Nick Jacobellis - Also by this author

The LWRC M6A2 SPR also proved to be an incredibly smooth shooting rifle. I believe this rifle shot so well because all of the internal parts are coated with a patented EXO Technology nickel alloy that protects against corrosion while also adding lubricity to all internal parts and mechanisms, including the trigger system. The LWRC M6A2 SPR also uses the Advanced Combat Bolt, which is designed to operate for 20,000 rounds.

During the next phase of our test the mid-length direct impingement Bravo Company EAG Tactical Model M4 was compared to the direct impingement Colt 6940 Model M4 carbine. Three out of four shooters noticed that the recoil impulse from the Bravo Company EAG Tactical shot noticeably softer than the Colt 6940. 

In our third range evaluation, we compared a direct impingement Colt 6920 M4 and a direct impingement Colt 6940 M4 to the Bravo Company EAG Tactical Carbine and the LWRC M6A2 SPR. The Bravo Company EAG Tactical Carbine was without question the softest shooting M4 of any rifle tested during this session. This rifle was equipped with a mid-length gas system as well as an incredibly effective Battle Comp compensator.

It should be noted that even though the Battle Comp compensator significantly reduces muzzle rise under firing conditions, this compensator does produce a loud noise signature. While this did not prove to be a problem for anyone operating the Bravo Company M4, the rifle sounded very loud to bystanders and other shooters. 

In the fourth range session, we compared the Bravo Company EAG Tactical to the LWRC M6A2 SPR. The Bravo Company EAG Tactical Carbine (M4) once again proved to be the softest shooting rifle tested. For the record, both the Bravo Company EAG Tactical Carbine that was equipped with an Aimpoint Micro T1 red dot optic and the LWRC M6A2 SPR (M4) that was equipped with an Aimpoint Comp M4 red dot optic produced almost identical sub-one-inch groups at 50 yards. 

Everyone who participated in the test and evaluation agreed that any well-made M4 variant that uses high-quality parts regardless of the operating system is a very capable rifle for law enforcement operations.

But a softer shooting rifle enhances precision and speed of engagement, and a mid-length direct impingement M4 like the Bravo Company variant or a mid-length gas piston LWRC M6A2 SPR shoots softer than a standard direct impingement M4.

A Quick Quide to AR Systems

Direct Impingement: The original Eugene Stoner design in use for decades. Uses hot gas from expended ammunition to drive the bolt to the rear.

Pros: Battle tested for decades, entry-level versions generally less expensive than other AR/M4 designs.

Cons: According to the U.S. military, reliability can be a concern under certain adverse conditions (Note: the author has never experienced a problem with direct impingement rifles that could not be attributed to defective or worn-out magazines), gets dirtier than other AR operating systems, recoil is noticeably heavier than in other AR operating systems, select fire versions can be prone to stoppage during sustained usage.

Mid-Length Direct Impingement: Direct impingement design with longer gas system.

Pros: Shoots softer than standard direct impingement model for faster follow-up shots, stays slightly cleaner than direct impingement model, reportedly very reliable. (The CEO of EAG Tactical says that he has shot 48,000 rounds through one of Bravo Company's mid-length direct impingement models with no malfunction.)

Cons: More expensive than an entry-level direct impingement model.

Gas Piston: Hot gas from the expended ammunition is used to power a steel rod or piston that pushes the bolt to the rear.

Pros: Runs cooler and cleaner than direct impingement ARs, improved reliability over standard model, select fire gas piston models tend to be more reliable than select fire direct impingement models.

Cons: Generally more expensive than direct impingement models, armorers used to working on direct impingement rifles need to be trained specifically to work on gas piston versions, additional expense can be incurred stockpiling spare parts for the more popular direct impingement versions and the gas piston models, some gas piston models can be retrofits of direct impingement rifles, which can lead to breakage of critical internal parts.

Mid-Length Gas Piston: A hybrid of the piston system and a mid-length system.

Pros: Most advanced M4/AR design, incorporates all of the best features of the mid-length direct impingement design and the gas piston design.

Cons: More expensive than standard direct impingement, armorers used to working on direct impingement rifles need to be trained specifically to work on mid-length gas piston versions, additional expense can be incurred stockpiling spare parts for the more popular direct impingement versions and the mid-length gas piston models, relatively new and unproven design.

For More Information:

Bravo Company



SIG Sauer

Nick Jacobellis is a medically retired U.S. Customs Agent and former police officer who was physically disabled in the line of duty while working as a federal agent.

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Comments (1)

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Bart3054 @ 1/30/2012 7:13 PM

The POF and the HK 416 were part of the initial resurgence of the piston in this platform, have to give a nod to them as well.

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