Cleaner. Cooler. More reliable. These are just three advantages cited by people who prefer piston-driven ARs over direct-impingement guns. The Stoner-type direct impingement system traditionally used in the AR-15/M16 platform bleeds off propellant gas from the bore and directs it through a tube to the bolt carrier group, which then cycles the gun. While the direct impingement system can be very reliable, there is no doubt that a lot of fouling can build up on the bolt carrier group.
Piston-Driven ARs
A growing number of companies build piston-driven AR-style rifles. These guns use the propellant gas to operate a rod that acts as an intermediary to exert force on the bolt carrier group to cycle the weapon. All excess gas is bled out of the gun well forward of the receiver. This helps keep the guns extremely clean when compared to the Stoner-type direct impingement system.
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There is a wide range of rifle configurations available with a piston system. Calibers run the gamut, as do barrel length, furniture and intended use. Here are some of the best piston-driven AR-style rifles on the market.
Adams Arms COR Ultra Lite
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The COR Ultra Lite rifle from Adams Arms features a 16.5-inch barrel with a 1-in-7-inch twist rate and a VDI Jet Comp. It uses a low-mass bolt carrier and comes standard with a Magpul MOE stock and pistol grip. The handguard is a Samson free-floating rail system. Diamondhead D-45 sights are an optional upgrade, as are Kryptek finishes.
Barrett REC7 Gen II
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For a compact rifle in 5.56mm NATO or 6.8 SPC, it is tough to beat the Barrett REC7 Gen II, which is available with either a 9.25- or 16-inch barrel. The 5.56mm barrels have a 1-in-7-inch twist rate, while 6.8 SPC barrels have a 1-in-10-inch twist rate. The REC7 Gen II comes with a KeyMod handguard, a Magpul MOE stock and an oversized triggerguard. The rifle can be ordered with a black, grey, OD green or Flat Dark Earth Cerakote finish.
Colt LE6940P
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Long associated with the AR platform, it should be no surprise that Colt offers a piston-operated rifle. Called the LE6940P, the rifle is chambered in 5.56mm NATO and uses all standard AR-15 magazines. The LE6940P come with a 16.1-inch barrel, folding backup sights and an adjustable buttstock. A quad-rail handguard also comes standard.
Heckler & Koch MR762A1
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Chambered in 7.62mm NATO, the Heckler & Koch MR762A1 is a reliable, compact rifle that offers better downrange performance than the typical 5.56mm. A 16.5-inch, cold-hammer-forged barrel is standard, as well as an adjustable buttstock, Troy flip-up front and rear sights and HK’s free-floating, quad-rail handguard. The rifle comes with a 20-round magazine.
Huldra Mark IV
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Aggressively priced, the Mark IV carbine from Huldra Arms offers users an economical way to upgrade to a piston-operated carbine. These 5.56mm NATO rifles have 16-inch barrels with a 1-in-7-inch twist rate and a Melonite finish. The rifles come ready for mounting optics with a Picatinny rail and a low-profile gas block.
LMT CQB MRP Defender Piston
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Designed for use in close quarters, the Lewis Machine & Tool Company (LMT) CQB MRP Defender Piston is a piston-driven AR available with either a 12- or 16-inch, chrome-lined barrel chambered in 5.56mm NATO. LMT cryogenically treats the barrel for longer life and improved accuracy. A quad-rail handguard and SOPMOD buttstock are standard features. The gun ships with tactical sights, rail covers and a sling with QD swivels. LMT also offers a 6.8 SPC-chambered gun with a 16-inch barrel.
LWRCI IC-SPR Individual Carbine
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The Individual Carbine line is built on LWRCI’s patented self-regulating short-stroke gas-piston systems that are more reliable, capable and longer lasting. It includes revolutionary new features like a fully ambidextrous lower receiver, dual controls for bolt catch and release, a magazine release and fire control group. The lower receiver is compatible with all legacy AR-15-pattern upper receivers. The monoforge upper receiver is machined with an integrated rail base that is lighter and stronger. Other features include a two-position gas block with normal and suppressed settings, and a spiral fluted barrel that is 20 percent lighter. Increased surface area speeds cooling. LWRCI Enhanced Fire Control Group is nickel-boron coated for a smooth crisp trigger pull with positive reset.
POF-USA P308 GEN 4
The Patriot Ordnance Factory (POF-USA) P308 is an AR-style rifle chambered for the 7.62mm NATO cartridge. Offering more long-range power than a typical 5.56 NATO gun, the P308 can be had with barrel lengths of 12.5 to 20 inches and be outfitted with a variety of precision optics. The rifles have ambidextrous controls and can be had in a variety of finishes, including Burnt Bronze and NP3.
POF-USA P415
The P415 from Patriot Ordnance Factory (POF-USA) combines the fast-handling characteristics of a light and handy AR carbine with the rock-solid reliability of a piston operating system. These carbines are chambered in 5.56mm NATO and come with barrel lengths from 7.25 to 16.5 inches. Magpul stocks, pistol grips and magazines come standard.
Primary Weapons Systems MK109
Light and compact, the MK109 from Primary Weapons Systems (PWS) gives users the increased punch of the 300 BLK cartridge from a 9.75-inch barrel. For those who want to employ a suppressor, this rifle can be extremely quiet. A KeyMod handguard is standard, as is the nickel-Teflon-coated bolt and carrier.
Sig Sauer SIG516 Patrol
The SIG516 from Sig Sauer uses a short-stroke piston system with a four-position adjustable gas valve to provide officers with optimum reliability. Chambered in 5.56mm NATO, the SIG516 uses standard AR-15/M4 magazines but adds an ambidextrous mag release for left-handed shooters. Flip-up sights, an adjustable buttstock and a quad-rail handguard are all standard.
Sig Sauer SIG716 Patrol
If you need the heavier hitting power of a 7.62mm NATO-chambered rifle, the piston-driven Sig Sauer SIG716 deserves a look. With a six-position buttstock and an ambidextrous magazine release, these guns are well-suited for a wide variety of users. QD-type sling attachments and iron backup sights are standard. The nitride-treated barrel is 16 inches long and has a 1-in-10-inch twist rate.
Stag Arms Model 8TL
Stag Arms is one of the few companies that make left-handed AR-style rifles. The Model 8TL is a left-handed version of the popular 8T, and it comes with all of the same features, including the chrome-lined barrel, Diamondhead components and an adjustable buttstock. Standard rifles are chambered in 5.56mm NATO, but the guns can also be had in 6.8 SPC.
This post was updated on Jan. 12, 2006.
