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Stag Arms Model 8 popular-priced piston gun: Fortier is a well-known piston skeptic, but he says if you want to try piston operation in an AR, this is a great place to start.

While Stag Arms is perhaps best known for its line of left-hand ARs, it also offers a full line of standard right-hand models. Until recently these were all conventional direct-gas guns, but now Stag has expanded into the piston arena with the new Model 8. Available in both right- and left-hand versions, this new model is yet another option to consider if you're in the market for a piston-operated AR. The question I had was, "Does it actually bring anything to the table?"


The rifle ships in a plastic hard case with manual and a 30-round magazine. At first glance, it simply looked like one of Stag's standard 5.56mm Model 3s. It's built on a flattop upper receiver mated to a 16-inch government profile barrel.

The barrel is chrome-lined and features a 5.56x45mm NATO chamber, 1:9 twist and sports the typical cut for mounting an M203 grenade launcher. This latter feature is fairly useless on a sporting rifle, but remains the norm.

I am not a big fan of l:9-inch twist barrels either. I'd rather have a 1:7 or 1:8 twist so I can shoot the entire range of loads available. However, 1:9 inch twist barrels remain the commercial standard because they split the difference between the original A1 1:12 twist and the A2 1:7. Fitted to the muzzle is a standard A2 flash suppressor. Handguards are the standard M4 pattern.

An A2 pistol grip is standard equipment along with a six-position collapsible stock. Inside are a standard weight carbine buffer assembly and a standard GI type trigger group. It really does look like a plain Jane AR until you get to the gas block. Then you notice something out of place, an adjustable gas regulator.

Taking a closer look you will note the beefy gas block is not a standard piece. This good-looking unit is pinned on for durability and features a 1913 rail at 12 and 6 o'clock. At its front is an adjustable and removable regulator. To adjust, simply depress a detent and rotate it to the desired position.





It has two positions, one which provides semi-automatic function and one which shuts the gas off to the system. To remove, depress the detent and unscrew counter-clockwise. The regulator is designed to accept a wrench, US GI cleaning rod or a cartridge tip if it is frozen due to fouling. By being threaded, the regulator is intended to be more robust and easier to remove than, say, an FAL gas plug. Pop the top handguard off and you get a surprise. The first thing you notice is the hand-guards only have one, rather than two, aluminum heat shields. A closer look also reveals the top handguard has been notched at its front to clear gas exhaust ports. This means the handguards are not interchangeable.

The next, and much bigger change, is the substitution of a short-stroke piston system for the Stoner gas tube. Removing the gas regulator gives easy access to the piston and return spring for cleaning. Very simple in form, Stag's system combines the function of a piston and tappet into one piece similar to POF's design.

Pop the upper open and you note the tappet impinges upon a redesigned bolt carrier. Stag has upgraded the carrier specifically to withstand the impact of the tappet and to prevent the carrier from tilting or twisting in the receiver. They accomplished this by machining the tappet impact point integral with the carrier.

Other companies have tried bolt-on and dovetailed pieces, but these will eventually fail. Stag's design is an entirely new carrier rather than a standard unit with a piece bolted on in place of the gas key. In addition, the rear of the carrier has been redesigned to prevent tilt and ease the transition from the receiver into the receiver extension.

The first time I took a Model 8 apart, I was surprised to find the bolt head under spring pressure. Interested to see what Stag had done, I pulled the carrier assembly apart. I found that Stag has added a small spring inside the bolt carrier itself. This pushes the bolt forward.

Why was it added and what does it do? It appears simply to hold the bolt in the forward position to aid in reassembly. Plus, in theory it will slightly reduce the cam pin pressure on the cam slot in the side of the receiver.

By design, Stag's new piston system will not foul the moving parts with carbon like a standard direct gas AR does. Plus it does not inject heat directly into the action. Removing the heat from the system will make the rifle run cooler and in doing so could enhance the service life of the rifle.

Removing the fouling from the action will make the rifle run cleaner and should aid reliability. Less fouling in the action will decrease user maintenance as well.

The Model 8 is finished off with Midwest Industries low-profile folding iron sights. Weight is a handy 6.9 pounds and overall length with the stock collapsed is just 32.3 inches. Fully extend the stock and the Model 8 is still very compact at 35.6 inches. My review gun was nicely finished, the bolt operated smoothly and the controls were easy to manipulate.

But how would it perform? That was the question. To find out I rummaged about my ammo locker and came up with three loads for testing. These consisted of Black Hills' 69-grain HPBT Match, Federal's American Eagle 62-grain FMJ and Wolf Performance Ammunition's economical 55-grain steel case FMJ. I felt this diverse array of loads would give a good indication of what these two rifles were capable of. Black Hills match would show the true accuracy potential. Federal's American Eagle load would indicate what a quality FMJ was capable of. Lastly Wolf's 55 grain load would show if it had any issues with steel case ammunition.

With a pile of magazines loaded and ready to go, I got to work. First up, I topped the Model 8 with a magnified optic for testing. I selected one of Bushnell's new 3-12x44mm Elite 4200 Tactical FFP scopes. This is a very interesting model with a Continental flair that sports a mil-dot reticle in the front focal plane, so you can mil targets at any magnification setting.



Complementing the illuminated mil reticle are target turrets with .1 mil adjustments. Optical performance of Bushnell's Elite 4200 is also very good. While a bit much for normal use on a small carbine, it would allow me to see just what kind of accuracy the Model 8 was capable of.

I fired four consecutive five-shot groups on paper at 100 yards. Accuracy was good for a lightweight semi-auto carbine. As to be expected, best accuracy was obtained with Black Hills 69-grain Match load. This averaged a respectable 1.2 inches at 2698 fps. The trigger on my review rifle, while stock, was actually pretty good. It exhibited just a bit of creep but broke cleanly and made the Model 8 easier to group off the bench.

Federal's 62-grain American Eagle load averaged 2.1 inches, while Wolf's 55-grain steel case load averaged 3.1 inches. Recoil was mild and the ejection of spent cases was consistent. All in all, firing groups at 100 yards from the bench was rather matter of fact.

Before removing the Bushnell, I put the Model 8 to work on steel from 125 to 400 yards. I had no problem hitting 11.5x20-inch LaRue Sniper targets at these distances from the prone position. At these ranges, I simply used the Bushnell's mil reticle for elevation/windage adjustments. Doing so provided rapid hits on the LaRues. Its light weight does make the Model 8 harder to hit with at distance, but if you do your part, practical accuracy is not an issue.

While Bushnell's 3-12x44mm Elite 4200 Tactical FFP is an excellent scope, it's not really the right optic for a carbine. So I popped the Bushnell off and swapped on an Aimpoint Micro T-l red dot sight. This is a great little red dot sight perfectly suited for use on the Model 8.

I then proceeded to burn up some Wolf steel case ammo running a variety of drills. During this portion of testing, targets were engaged from 2 to 100 yards. Thanks to its light weight and short overall length, the Model 8 performed very well. It proved quick handling and easy to hit with.

One point I'd like to make is that many of the AR piston guns on the market today are fairly hefty. The Model 8, on the other hand, is very light and handy. I did note its recoil impulse is different than a direct-gas gun. Not bad, just different.

Reliability of the Model 8 was excellent, but not perfect, during my limited testing. I did have a couple of cases fail to eject fully.

Other than that, the Model 8 simply chugged away. After firing three 30-round magazines at a rapid rate, I noted the bolt carrier was still cool to the touch. Plus, the action was almost as clean at the end of testing as when I started. Keep in mind this is a 6.9-pound carbine, not a competition rifle. It is more than capable of doing its job.

My wife is active-duty Army and her issue weapon is an M4 carbine. So I asked her to run a few rounds through the Model 8. She had no problems making rapid hits on target during drills. Afterwards she commented that in her opinion recoil felt very similar to her M4. One aspect she really liked was how clean the bolt carrier and receiver were. She also liked the light weight of the piece.


One aspect of the Model 8 many shooters will appreciate is how easy it is to clean after a day on the range. It takes much less time than a conventional direct-gas AR. Yes, the gas port and piston require a little bit of elbow grease, but it's no more difficult to clean than any other piston system. You will want a tool handy, such as a length of cleaning rod, to remove the gas regulator, though. The carrier group and receiver are easily wiped clean.

All in all, Stag's Model 8 is a no-frills piston AR devoid of bells and whistles. There are no rails, fancy coatings or widgets. It's just a basic carbine that easily accepts optics. The piston system is not as refined as some others, and I will be interested to see how it holds up to heavy long-term use. On the plus side, Stag's design is very simple to strip for routine maintenance.


One nice thing about the Stag Model 8 is the retail price. It is by no means inexpensive, but at $1,145 retail, the Stag Model 8 is less expensive than most of its piston competitors. So if you're looking for a basic piston AR, Stag's Model 8 is one to consider.

Accuracy Chart

Load      Bullet Weight  Muzzle Velocity  Standard     Average
             (grs.)         (fps)         Deviation  Group (ins.)

Black Hills HPBT Match

               69            2698             14         1.2

Federal American Eagle FMJ

              62             2729             42         2.1

Wolf FMJ

              55             2802             35         3.2

Notes: Accuracy results are averages of four five-shot groups fired
from a rest at 100 yards. Velocity figures are 10-shot averages
recorded by an Oehler 35P chronograph placed 12 feet from the muzzle at
an ambient temperature of 83[degrees] F at 1030 feet above sea level.


Stag Arms

860-229-9994 |


703-263-9795 |

Black Hills Ammunition

605-348-5150 |


800-423-3537 |


Midwest Industries

262-896-6780 |

Wolf Performance Ammunition

888-757-9653 |



Manufacturer: Stag Arms, New Britain, Conn.

Action Type: Short-stroke gas-piston with rotating bolt

Caliber: 5.56x45mm NATO.

Capacity: 30-round detachable box magazine

Barrel: 16-inch chrome lined with 1:9 RH twist

Overall Length: 35.6 inches with stock fully extended

Weight: 6.9 pounds without magazine

Furniture: M4 collapsing synthetic, A2 pistol-grip, M4 handguards

Finish: Hard anodizing and phosphate

Trigger pull: 6.5 pounds

Sights: Midwest Industries folding low profile BUISs and 1913 optics rail

Price: MSRP $1,145

RELATED ARTICLE: To piston or not to piston, what is right for you?

Is a piston AR something you should consider? Maybe, maybe not; they are certainly not for everyone. While I remain very happy with my direct-gas guns, I am well aware there is currently a lot of interest in piston-operated ARs.

As is to be expected, both the traditional Stoner direct-gas and contemporary piston systems have certain strengths and weaknesses. Neither is perfect, and anyone who says one or the other is the Holy Grail is simply trying to sell you something. While neither is without faults, both have some very desirable features.

In defense of the traditional Stoner direct-gas system, it is a very simple and well-proven design. The Rossignol inspired gas tube has no moving parts and doesn't interfere with barrel harmonics like a piston system can.

Parts for a direct-gas gun are also readily available and basically universal from manufacturer to manufacturer. This is a very real plus and something to consider as well. Contrary to what some may lead you to believe, a direct-gas rifle will be very reliable if built from quality parts. Accuracy of this system is excellent and has become the yardstick by which all semi-automatic systems are measured. It's also a very flexible system which works well with a wide variety of cartridges and barrel lengths.

Critics point out how the design vents propellant gas directly into the bolt carrier assembly, and tend to use the term "self-fouling." Fouling is greatly increased when a sound suppressor is mounted. Fouling is not the only thing vented into the bolt carrier assembly. A great deal of heat is also deposited there as well. Heat, of course, is the enemy of any mechanical device.

So this system both heats up quicker and takes longer to cool down. In addition, when 5.56x45mm caliber carbines are fitted with very short barrels, less than 12.5 inches, reliability can be problematic.

The various gas piston designs, both long and short stroke, address some of these issues. While piston systems have become popular in the civilian market during the last few years, the idea dates way back to designs like the Armalite AR-18 or Daewoo K2.

Substituting a conventional piston for the Stoner system eliminates hot propellant gas from being vented into the system. In doing so the amount of both fouling and heat introduced into the receiver/bolt carrier assembly is dramatically reduced. This is especially true when a sound suppressor is mounted. Plus piston designs can be more reliable on carbines with very short barrels.

The downside to a piston system on an AR is that Stoner did not intend it to be operated with one. The bolt carrier, receiver and receiver extension were not designed for the bolt carrier to be pushed in the gas key area by a piston.

While the direct gas system drives the bolt assembly straight back, a piston impacts the carrier away from its axis, tilting and twisting it. This can give rise to what is called "carrier tilt," where the nose of the carrier lifts slightly and its tail pushes down. If not corrected carrier tilt can lead to premature parts wear and failure.

While a piston-operated design does not vent fouling directly into the action of the rifle, it will still foul to some degree at the gas port. Anyone who has ever cleaned the piston on a FAL understands this. Also a moving piston can have a negative affect on accuracy if it is not timed correctly. This can lead to, among other things, vertical stringing.

A piston also introduces additional parts into the system, adds weight and increases cost. It should also be understood that all the current piston systems were designed independently and utilize proprietary parts. So replacement parts for the various piston systems are only available directly from the individual manufacturer.

Lastly, while the original Stoner system has been around for more than 50 years, the latest crop of piston designs available here in the USA are relatively new. Due to this many companies are still learning what works, what doesn't and why.

When it comes to ARs I am admittedly more than a bit jaded. For the most part, I prefer direct-gas guns which are relatively basic in form, less expensive in price and have universal parts availability. I find simplicity, within reason, a virtue.
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Article Details
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Author:Fortier, David M.
Publication:Shotgun News
Article Type:Product/service evaluation
Date:Jul 20, 2010
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