Range Reports

Range Report: Piston-Powered Stag Arms Model 8T

Stag Arms Model 8T Right Side with Inset

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.

Stag Arms Model 8T Diamondhead Front Sight
With the front sight deployed, the Diamondhead system offers a unique sight picture that is fast and precise.

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.

Stag Arms Model 8T Diamondhead Front Sight Folded Down
This is the Diamondhead front sight folded and stowed; just in front of the sight is the piston gas plug.

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.

Stag Arms Model 8T Diamondhead EoTech Sight
EoTechs and AR carbines are a good combination for close-to-medium-distance situations.

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.

Barrel Length 16 inches
Caliber 5.56 NATO
Weight 6.9 lbs.
Sights Diamondhead flip-up
Stock Mil-Spec six-position type
Trigger Mil-Spec, single-stage
Finish Matte black, type 3 hard-coat anodizing
MSRP $1,275

Stag Arms Model 8T 5.56x45mm/.223 Rem. Range Performance

Load Muzzle Best Average
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.

Stag Arms Model 8T Quartering, Front Right
The author says that if you are perceptive, you will feel a difference in balance between an impingement and piston carbine; the piston is slightly forward heavy.

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.


The Mission of Cheaper Than Dirt!'s blog, The Shooter's Log, is to provide information—not opinions—to our customers and the shooting community. We want you, our readers, to be able to make informed decisions. The information provided here does not represent the views of Cheaper Than Dirt!

Comments (25)

  1. I purchased the model 8t. After a 11 week wait before it shipped, I received after a 12 week wait.
    Out of the box, feed ramps gouge the bullet and jambs (bolt open, round stuck on feed ramp) resolved; slightly ground edges and polished ramps.
    62 grain greentips cycled fine.
    Went to some 55 grain fmj, short strokes almost every round! Gun fires, bolt fully closed, klick! No round in chamber. And with good quality brass ammo.
    Not what I expected from a $1200 stag.
    And shipped with fixed stock(i prefer this) but was advertised to ship with 6 position adjustable stock.
    I must say, another manufacturer going down the S$&@ Tube.

  2. I prefer piston designs. I like coming home with clean, cool bolt. Sure, both designs are mostly reliable. I believe the piston design, if done correctly, is superior for reliability. And I’m OK with any performance hit like extra recoil. I see a lot of newer gun designs are piston. I think there is a reason for that. And I mean new designs, not just AR15 knock-offs, but unique designs not common to the AR platform. A short-stroke piston is a good compromise design. I like those.

  3. My eyes arent that great anymore! Do you have a PH if a guy wante to buy a gun from you send it my way. I have my 7.mm mauser, shot gun, 22 savage, 45 auto witness. What I need is something thats acurate great at long distance and close in. I need conversation. Oh I have bought ammo from you and I would want to be able to buy rounds reasonably priced.
    Sincerly DB Anderson Send me your phone number.

  4. Well since everyone wants to comment I figured why not throw my 2 cents worth in. I have carried in COMBAT (DGI) issue rifles by both Colt and FN. Granted it was 20 years ago and they were the M16A2 (by both) and the CAR 15 (Colt). I can honestly state I NEVER had malfuntions due to the gas system. Alot due to magazines but not the gas system. I never heard of a gas system related malfunction in the Corps back then either.
    Now that I am old and lazy I hate the tedious task of cleaning a DGI rifle. The piston systems have the easy cleaning award hands down.
    Accuracy was brought into the mix. I think you need to check twist rates before comparing accuracy. I have GI spec rifles that shoot well with 55 to 62 grain but can’t hit a barn at 300 yards with 72 to 77 grain match ammo. On the other hand I have LWRC rifles that will circumcise a gnat at 300 yads with 77 grain match ammo, but shoot AK style groups with 55 grain ammo at the same distance. TWIST RATE MUST MATCH BULLET WEIGHT TO GET ACCURACY.
    Now to weight. Yes the piston systems add weight. About 2-3 ounces. That’s really heavy. (LAUGH NOW). Maybe the piston rifles are heavier due to all the s… being hung from them. Don’t get me wrong I like the rail systems. They would have been great back when I was in. Zip tieing or hose clamping a mag light to a rifle sucked. I’ll take the ACOG over iron sights or.the old 4 Colt scope any day.
    My point is simple.. compare apples to apples. Not apples to watermelons.
    Piston rifles can’t be that bad, Uncle Sugar issues the he’ll out of them. My favorite of the many I have tried is LWRC. Great rifles. Accurate, durable, dependable and you don’t have to do anything when you add a suppressor. Just pull the trigger.

  5. I Have A STAG2T,Very Accurate With ACOG And BUIS As Well,Had It Two Years Now And Will Be The Weapon I Take When I Use My Guardian Membership At Front Site Academy 4 day AR15(M4) Tactical Course,And One Night Course I Believe As Well,I Cannot Wait.I Have To Say This,I Have NEVER Had A Problem With My Stag2T In Any Area As Of Yet(FINGERS CROSSED,LOL!!!),But Don’t Want To Jinx My Self!!!!Anyways I Have Found ALL Stag Weapons That I Have Had The Honor Too Shoot,To Be All Squared Away!!!Thank You!!! SINCERELY,JAMES.

  6. I have been happy with my Model 3. It shoots 1.5″ groups with a SightMark Red Dot. Planning on switching to my favorite scope…a vintage Weaver K6 from my 7×57 custom Mauser that shoots 3/4″ groups.

  7. Piston is better but not standard. Gas is standard but not as good. We need the military and the manufacturers to agree on standard specs and design for a Piston system (preferably without need for a buffer tube) so we can have the best of both worlds.

    1. Piston isn’t better… They each have their place, each one does something a little better than the other. Now if you want to put the piston versions up against the original A1s then you’re right, they will shine. Most of the people that have problems with their DI AR’s are the ones who are lazy and never clean their rifles.

      AR’s made now-a-days are built using better manufacturing techniques and with better technology and better materials. I have two AR’s, one I built back in 1999 and one I just finished building last month. Neither of them has ever fouled or had any issues.

  8. The Colt Military testing of the M4 weapon system in 1995 revealed gas tube bursting after 586 rounds of sustained fire. Military testing of the AK47 (mentioning this only for the reliability of a piston operating system) revealed no malfunctioning after 2000 rounds of sustained fire. Here is your proof of piston system reliability, along with the thousands of rounds fired by our troops through countless SCAR and HK416 rifles that are also piston driven. Both systems are good, but the impingement system needed improving.

    1. Pistons belong in motors and antique Russian guns. Definitely not in any of my Modern Sporting Rifles. Over 20 years and 20,000 rounds on my first build and never a hiccup with the same tube, and I only cleaned it out a couple of times. I had an SKS and AK47s and yes they all went bang but over 100 yards and you’re praying to hit your target. my m4 will take off the head of an ak carrying target at 400 yards. Additionally they add more weight to a rifle that was built to be light and perfectly balanced. Impingement all the way!

    2. You are talking about a 20 year old test my friend. How many versions of the AR have come out since then? AR’s made now-a-days are built using better manufacturing techniques and with better technology and better materials. Why don’t you find tests done within the last 5 years using the newer AR’s proving your point and then you will have people listening and believing what you are preaching.

  9. As an NRA High Power Rifle – Master-Classified shooter, and general AR-15 gunner, the gas impingement (GI) system is the most accurate, and has been proven, by billions of rounds fired, to be >99.999% reliable.

    The piston system (PS) may be equally reliable, but accuracy-wise, still unproven to meet that of the GI system. I know of NO ONE who shoots a PS-driven AR in NRA HPR.

    The most distressing aspect of the PS is that there is no industry standard on the piston, bolt carrier, etc. If your GI system goes down at the range, someone is there with spare parts or the know-how to get you running & gunning again. If your PS fails, you are probably limited to, at best, a manual, charging-handle operated repeater.

    Also, as a systems, reliability, compliance engineer, I go with the proven, most simple, most common, easiest-to-fix designs before putting myself & my life on the line.

    As Sloan stated, “It’s all in how you use your AR”. I will add that nowadays, it makes less difference on who makes it in order to get great quality/accuracy. I have AR’s that span both ends of the name/price spectra that shoot equally as well, and I demand <0.75 MoA from all my rifles.

    You will do well with either the GI & PS, but you better hope you will never need to repair the PS on the fly.

  10. I am a former soldier & I have had both types of systems. The biggest disadvantage of a piston-system AR is the weight. When you’re walking hundreds of miles carrying all of the equipment, food, water, & ammo you may need for the mission every ounce counts. In my opinion, many of supposed problems of a gas impingement system are put out there by people who have never used their weapon anywhere other than the range. Yes, gas-impingement system do make the bolt & bolt carrier a little harder to clean, but I’ve never had one fail on me because it was dirty. Eugene Stoner designed the AR to have relatively loose tolerances so that they would operate in some pretty bad conditions. I’ve had my issue weapon in mud, water, sand, snow, as well as having put thousands upon thousands of rounds down range and just about every condition you could imagine, and never had a malfunction due to the impingement system. The only real problem I ever had was with the collapsible buttstock on the M4, & the buffer, periodically.

  11. I have had my model 8 for about 4 years now and it has never coughed once. I have shot and competed with this gun rights alongside the mighty Noveske, Daniel Defense and other high end ARs and stayed right with them. Had I been the shooter I was 15 years ago I would have whipped every one of those guys hands down with my model 8. It is a fine weapon I would carry without hesitation into any fight, anywhere anytime. IMHO, these weapons should be standard issue for our brave troops wherever they serve.

  12. I considered this rifle when I was shopping for an AR style rifle. As a left handed shooter I also considered a lefty model. My consideration is due to the amount of propellant that comes back at you out of the ejection port. As a lefty that goes straight in my face. So for that, and for the thought that I can leave it for extended periods and not have to worry too much about firing it dry.

    1. Nater – I too am a lefty and for this reason alone I was looking something that didn’t throw the brass back at me — I actually just got my model (8T-L) along with my Kel-Tech KSG shotgun just last week. Next I may look at a Rock River as I’m told they make a lefty AR as well.

    2. FWIW, I’m a lefty and built an AR recently using a Stag Arms 2HTL upper (I got a lower from JD machine and a lower parts kit from Stag). It’s pricey but I really like my new AR. So far I have put 1000 rounds through it at the local indoor range without cleaning and it’s still running good. Mostly cheap Tula and Federal ammo. I’m going to give it a good clean before our next trip to the range but wanted to see if the DI system could handle 1000 rounds without jammming and it did… I’m planning on mounting a nice 3-9x leopold scope before our next trip to see what she can do at 200-300 yards (my eyes aren’t that great), but so far I’m stoked on this lefty setup. I have shot several ARs (all righty) and this rifle is by far my favorite. Now I want t build the same gun in .308… 🙂

  13. I have both gas impingement as well as the Stag Arms Model 8 piston gun. All three are very accurate and I enjoy shooting them equally as well. The advantage of the piston system is cleanliness as well as being a cooler running rifle.My Stag has a scope mounted to it and is used for hunting. My gas impingement RRA 5.56 has a EOTech XPS2.0 mounted and is primarily a self defense weapon. My other gas impingement setup is the RRA lower with a Stag Arms 6.8SPCII upper. It wears a Leupold MK AR scope and is used strictly for hunting. Accuracy between the two systems is pretty much the same. Cleaning the piston system is a snap whereas the gas impingement gets dirtier and requires more time to clean it up internally. Get whatever floats your boat. You can’t go wrong either way.

    1. Using a direct impingement system on a M-16A2 and AR-15 ( Have used FN, Colt H-BAR, Mohawk, Stag, Bushmaster ) I can tell you that I’d rather stick with a piston driven system. In DI the gas tube heats up ( I have seen them red hot and the fore grip untouchable ) and the weapon is always dirty ( from the spent gas ), then there is the issue of heat in all those parts. I cannot see how any of that is good for the function of the weapon over time. Actually the failure rate is reasonably high. When I say that I am not talking about tossing a few rounds down range to sight in your optics every few months or the occasional 30 to 120 rounds at the range or back yard fun. It’s all in how you use your AR and who made it. For me, the next investment in a rifle will be a Piston driven set up.

    2. “The failure rate is reasonably high” According to your opinion or actual factual evidence from thousands of weapons in the field??

    3. I call B.S. on just about everything you said. I would rather have a warm dirty rifle that works than an unproven carrier and upper combo. Piston systems have an uncontrollable torque affect on the carrier and does damage the upper and the bearing surfaces of the carrier. This goes against the claim of “more reliable’. the AR is designed to use the cushioned force of the gasses not the slap of a damaging piston. It just wasn’t designed that way. You should invest in a SCAR or a good AK comrade. oh BTW in the field or at the range in 20 years I’ve never seen a gas tube fail… even glowing.

    4. Me Neither Taylormade,The Gas Impingement System,To Me Anyways,Is The Far Better Choice When It Comes To This Argument.The SCAR Is A Really Nice Weapon,That Someday I Hope To Get In 7.62X51,But For Practical,Know Its Gonna Shoot Everytime I Pull The Trigger,Especially In CQB,I Say The Gas Impingement On The AR’S Is Practically Unbeatable,Hell It Was Designed To Keep It’s Self Clean There,And Like You,I Have Never Had A Problem With It,And Only Ever Cleaned It When An Inspection Or Some Such Crap Was About To Happen,Of Course In The Field You Want To Keep EVERYTHING,Lubed And Cleaned,So In The Field,During Down Time I’ll Run A Few Pipe Cleaners Through It,Better Safe Than Really Sorry.But All In All,The Impingement System Quite Honestly Keeps It’s Se;f Pretty Clean.Thank You, James.

    5. It’s people like you who spew falsehoods without showing any evidence to back up all your idle chatter… I have two DI AR’s, one that I built back in 1999 which has many thousands of rounds through it without a single hiccup. Then I have my new build that I just finished last month and which already has over a thousand rounds through it again without any hiccups. And I typically shot 400-600 rounds through mine during each range visit, my free float handguard never gets red hot to the touch. Come back when you have concrete evidence to back up your incorrect innuendo.

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