Daily Bulletin » Gas Piston

Superformance Ammo in Gas Guns — Hornady TECH Advice

Editor — Wed, 11 Dec 2013 13:15:40 +0000

For many cartridge types, Hornady Superformance ammunition provides enhanced velocity compared to some other types of factory-loaded ammo. However, Hornady has found that there may be issues when Superformance ammo is shot in gas-operated guns with barrels under 20″, or with barrels fitted with suppressors. This is because the gas returning from the barrel port may cause the bolt to begin unlocking prematurely. Hornady has published the following information concerning the uses of Superformance ammo in direct impingment and gas piston self-loading rifles.

Internal Ballistics of Superformance Ammo in Semi-Auto Guns

Superformance™ ammunition is tested and is safely within SAAMI pressure guidelines. Gas operated (direct impingement or gas piston) firearms are perfectly safe to use with Superformance ammunition. However, Hornady ballisticians have conducted testing with a variety of guns (including guns equipped with suppressors), and our findings conclude that some systems work far better with Superformance ammunition than others.

It is recommended that to get the best functioning with Superformance ammunition in gas operated/gas piston semi-automatic or select fire guns, rifle length gas systems with 20 inch or longer barrel lengths are best for reliable firing and extraction. Any other configuration — particularly shorter barrels/gas systems — are best served with the installation of an adjustable gas system, ESPECIALLY if a suppressor is to be installed.

Due to the longer duration of peak pressure produced by Superformance, the post peak/declining port pressure at common carbine and mid-length gas port locations is still higher than that produced by standard propellant. This has a tendency to flood the system with a larger volume of gas, at a higher velocity, that tries to open the bolt of the gun too fast. It’s a timing issue. The cartridge case is still swollen from the application of pressure during firing while the gun is simultaneously trying to extract the cartridge case before it has had an opportunity to settle back to its original size, or more simply: the gun is still in the process or firing while it’s trying to extract the cartridge case.

If the firearm and the ammunition are not in sync, there can be what is commonly identified as “pressure signs” on the cartridge case. This is exhibited by the movement/marring of the head of the cartridge case, cratered primers, flat primers, ripped or ruptured cartridge cases, “popped primers”, and/or any combination of these effects. If any of these “pressure signs”; are apparent, stop firing immediately. If an adjustable gas system is installed, it is advisable to reduce the amount of gas flowing through the system by closing the gas port until the gun operates correctly.

With the installation of an adjustable gas system, gas pressure can be metered to a point that enough gas is applied to open the bolt, but at a slower rate to allow the cartridge case to return to its original diameter prior to the movement of the bolt, and thus allow for proper extraction.

Pressure VS Gas Port Location

Due to the longer duration of peak pressure produced by Superformance™, the post peak/declining pressure at common carbine and mid-length gas port locations is still higher than that produced by standard propellant. However, there is very little difference in port pressure between Superformance™ and standard propellants at the rifle length port location.

Superformance and Suppressors

The use of suppressors on rifles creates yet another dynamic in firearms design that is not commonly understood or communicated. Consider the suppressor on a firearm the same as a muffler on a car. The suppressor works as a filter for the gas (noise) that is escaping the barrel during firing. As a “filter”, it takes longer for the gas to leave the confines of the firearm, and thus, it creates back pressure. This back pressure, ESPECIALLY in a gas operated firearm forces an extensive amount of gas back through the firearm’s operating system that may create too much thrust too early during the firearm’s cycle of operation.

To counteract this back pressure, the use of an adjustable gas system is advised. By metering the gas system to ensure that it will cycle the firearm correctly and not flood the system with gas/pressure, the gun will work properly and will still benefit dramatically from the increased velocity potential of Superformance ammunition.

Back Pressure from Suppressor

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MEDIA Day Shoot: New MR762A1 LRP .308 from Heckler & Koch

Editor — Fri, 25 Jan 2013 17:49:08 +0000

There were many semi-auto “tactical” rifles on display at MEDIA Day 2013, but one that caught our eye was the new MR762A1 LRP from Heckler & Koch (HK). The HK MR762A1 LRP (“Long Range Package”) looks similar to the H&K G28 rifle, Germany’s new Designated Marksman Rifle. But the G28 has a steel upper receiver, unlike the MR762A1, which evolved from the HK 417.

Bedecked with quad rails up front, this black and tan rifle screams “tactical”, yet it is surprisingly comfortable to shoot. The grip is comfortable in the hand and the thick rubber buttpad on the adjustable buttstock did a good job of mitigating recoil. Jason said the trigger was crisp and the gun was very accurate. With a gas-piston system (rather than direct gas impingement), this rifle runs very clean. The proprietary, polymer HK magazine worked perfectly with zero feeding issues. We liked these better than the metal mags we’ve tried on other makers’ AR10-type systems.

The MR762A1 is a direct descendent of the HK416/417 series, only in a semi-automatic rifle configuration developed for civilian users. The MR762A1 LRP employs the same HK proprietary gas piston operating system found on current HK rifles and carbines, using a “pusher” rod in place of the gas tube in the original M16/AR15/AR10 design. According to HK, the op-rod design “virtually eliminates malfunctions common to direct impingement gas systems since hot carbon fouling and waste gases do not enter the receiver area. The MR762A1 stays cleaner, reducing heat transfer to the bolt and bolt carrier, and drastically reducing wear and tear on other critical components.”

The MR762A1 uses the same 10- and 20-round translucent polymer box magazines made for the HK417; a 5-round magazine is also under development. Additional accessories and add-ons for the LRP variant of the MR762A1 include an ERGO Pistol Grip from Falcon Industries, the same Blue Force Gear sling used on the HK M27 IAR supplied to the USMC, and an OTIS cleaning kit. The rifle package, complete with one 20-rd mag and one 10-rd mag, is shipped ready to use with the scope attached in a 42″-long Model 1720 Pelican case.

Colt Releases New Gas Piston AR Platform Rifle — LE6940P

Editor — Mon, 09 Apr 2012 20:21:10 +0000

Six decades after the introduction of the M16, Colt has added a gas piston system to the venerable AR15. Colt put a gas piston in this new AR-platform rifle in order to improve reliability and reduce fouling. The new gas-piston Colt AR, designated the LE6940P, will be sold to both civilians and law enforcement agencies. In selling a gas-piston AR, Colt is following the lead of Heckler & Koch (HK 416) and other manufacturers who have found a market among buyers seeking a lower-maintenance AR with significantly less internal powder fouling than the original direct-gas-impingement AR design.

Colt’s product press release declares: “Colt Defense LLC … has advanced its one-piece monolithic upper receiver to introduce the LE6940P. This modular carbine has an articulating link piston (ALP) operating system and offers shooters a highly accurate, lightweight and easy-to-clean AR-platform rifle with an extended lifespan. The advanced piston carbine (APC) is a lightweight, highly accurate alternative to the traditional direct gas impingement system found in most ARs. The LE6940P utilizes a unique articulating link piston (ALP) operating system, which reduces inherent stress in the piston stroke by allowing for deflection and thermal expansion. As a result, shooters are offered a highly accurate firing experience and the weapon’s lifespan is extended.”

Piston Design Developed for U.S. Military
“The new LE6940P puts to use a new, improved version of a piston system that Colt originally pioneered for the U.S. Army,” said David Ridley, Vice President of Colt Defense LLC. Ridley added: “Colt was the first to put a piston system in an AR, and we have continued to improve on that system since. Now, any civilian shooter or law enforcement professional has the opportunity to shoot using this superior piston-operated AR.”

Monolithic Upper with Extended Rail
The LE6940P weighs just over 6.5 pounds, and measures 35 inches with stock extended. The rifle is chambered in .223 Rem (5.56×45 NATO) and uses standard AR15 magazines. Colt delivers the LE6940P with a full-length rail running from the rear of the upper receiver to the front sight. This allows many mounting options for sights and accessories. Colt has also includes a back-up iron sight (BUIS) and a folding front sight. The lower receiver is marked “Piston Carbine” and comes with a Colt/Rogers Super-Stoc M4 H-buffer stock kit with cam-lock lever, push-button QD swivel, and accessory kit. The standard barrel is a 16.5″-long M4-type contour with flash-hider. CLICK HERE for large photos of the internals, plus close-ups of the folding sights.