Stag Arms makes a number of traditional gas-impingement-system rifles as well as some piston guns such as its Model 8T. From the outside, the 8T looks like any other Stag AR, except the 8T wears high-end furniture. The Model 8T also free-floats a 16-inch barrel in a Diamondhead VRS-T handguard, which is smaller in diameter to Mil-Spec handguards and is easy to grasp. I recently had a chance to take an 8T to the range along with a similarly configured gas-impingement rifle, and here’s how it performed.
The Model 8T had an upper constructed of forged Mil-Spec 7075 T6 aluminum with type 3 hard-coat anodized finish. It included a forward assist. The 16-inch barrel was 4140 steel that was chrome-lined with four grooves. The twist rate was 1:9 inches. It follows the government profile and sports a manganese-phosphate coating. The muzzle device was an A2 flash hider. The lower sported a six-position collapsible stock. The fire selector, or safety switch, and magazine release were standard Mil-Spec types, and the pistol grip was a standard A2-style unit made of toothy checkered polymer. The buffer and spring were standard carbine spec items. The trigger was a Mil-Spec single stage. It was adjusted at the factory to break between five and eight pounds.
Notches in the handguard allow the shooter to grip it better and pull the gun into the shoulder. It also allows a user to customize the handguard with rails. The handguard is drilled and tapped at the three, six and nine o’clock positions. Oblong vents are located on the top end along the left and right sides. Larger vents are located along the bottom. From the top of the receiver to the end of the handguard, a Picatinny rail provides numerous choices to place an optic. Under the handguard is the piston system. The slots in the handguard help to cool the weapon under hard use.
Disassembly is the same as with an impingement system, except the piston system requires the piston to be disassembled for cleaning.
I found the flip-up Diamondhead sights offered excellent target acquisition. At 25 yards offhand, I was able to easily shoot 2-inch groups as fast as I could press the trigger. I attached an EOTech XPS2 holographic sight, which mounted quickly on the carbine and was at the right height to align my eye when using an AR-style stock. When using the EOTech off a rest, the gun’s group sizes shrunk dramatically.
I had a direct-impingement carbine set up similarly for comparison, and in rapid-fire, I could feel the difference in recoil between the two systems. I have also fired full-auto piston and gas systems. In full auto, the piston system was slightly easier to control, but that point is moot on a civilian firearm.
For cleaning, the bolt-carrier group could be removed from the upper after extensive shooting without burning fingers. I also liked the idea that the bolt-carrier group can rack up high round counts without cleaning. On the other hand, parts for a piston system are more expensive.
When the brass has cooled, the main thing is to have an AR that will run when you need it. In my tests, the 8T performed flawlessly, even with the low-cost ammo I ran through it. I shot tiny groups with it — even off-hand. In the end, reliability and accuracy like the Stag 8T demonstrated are hard to beat in a consumer firearm.
|STAG ARMS MODEL 8T|
|Barrel Length||16 inches|
|Stock||Mil-Spec six-position type|
|Finish||Matte black, type 3 hard-coat anodizing|
Stag Arms Model 8T 5.56x45mm/.223 Rem. Range Performance
|American Eagle 55-gr. FMJ||2,971 fps||1.13 in.||1.44 in.|
|Independence 55-gr. FMJ||3,164 fps||1.38 in.||1.69 in.|
|Herter’s 55-gr. HP||2,750 fps||1.50 in.||1.69 in.|
Notes: Muzzle velocity measured with a ProChrono digital chronograph. Group sizes are the result of three five-shot groups at 25 yards shot with open sights.
Gas Impingement Versus Piston Mechanisms
Want to start a “healthy discussion” among AR shooters? Just ask them what’s better — an AR with an impingement system or a piston system. The basic arguments boil down to opinion and certain characteristics.
Those on the impingement side say the direct-impingement system is the original operating design in the AR platform. Gas from a fired round is ported through a small hole in the barrel and directed through a gas tube, where it contacts or impinges the bolt carrier, pushing it rearward. While this system channels heat and burning powder residue into the mechanism, it creates a smooth operating system with little felt recoil.
Gas-piston advocates have a slightly different pitch. A gas-piston system also uses propellant gases bled off through a hole in the barrel similar to gas impingement, but the gases are channeled into a cylinder-and-piston configuration. The gas moves the piston rearward, which pushes the bolt carrier to cycle the mechanism. This system keeps the bolt-carrier group cool and clean. In some cases, thousands of rounds can be fired through the gas-piston design without cleaning. On the downside, many shooters say the gas-piston system creates a snappy recoil, which can impact fast follow-up shots. They say the handguard also heats up under extended use.
Do you prefer gas impingement or piston mechanisms? Why? Tell us in the comment section below.