Tag Archives: AR 15

Tactical Rifle: Ruger SR-556

The last time I wrote about the AR-15 rifle platform my biggest design complaint was the Direct Gas Impingement (DGI) action.  This has been a feature since the very first generation of the weapon adopted by the military over 45 years ago.  DGI contributes to the platform’s simplicity and lightness, but also has some undesirable consequences: Every time the gun fires it blasts hot propellant gasses back into the bolt carrier, baking a layer of carbon onto everything in the receiver.  Decades of military service have proven that well-made AR-15’s can withstand this abuse and continue to function reliably with just basic cleaning and lubrication.  But for obsessive owners who like to keep their guns in more immaculate condition this dirty design can be quite irritating.

When I bought my first AR-15 following the 2004 expiration of the federal “Assault Weapons” Ban I openly wondered why no manufacturer had produced a piston-driven variant of the gun, especially given the huge market for America’s favorite tactical rifle.  Since then I tracked the gradual emergence of AR-15 piston actions, first as retrofit kits, then as new uppers and complete guns.  There was a great deal of concern about the long-term reliability of converted actions, mostly because the AR-15 bolt carrier wasn’t designed to be hammered with a piston, and its geometry seemed prone to an adverse effect called “bolt carrier tilt.”  Some manufacturers, most notably LWRC, built a new action from scratch to mitigate these concerns.  However LWRC’s piston uppers were always very hard to acquire, and even today they command huge premiums.

In mid 2009 Ruger entered the AR-15 market for the first time, and they did so with a proprietary piston action.  The SR-556 now represents the best value in piston-driven AR-15s.  I sold my old DGI AR-15 to somebody less fastidious than me and last month managed to pick up a new SR-556 for just under $1500.

The SR-556 comes standard with a number of desirable upgrades over basic AR-15s.  Among them:

  • Full-length quad-rail handguards, so you can easily add as many accessories as you can carry.
  • Top-quality folding iron sights (by Troy Industries).
  • A comfortable pistol grip (by Hogue).
  • Chrome-plated bolt carrier assembly, so what little dirt does get into the action can easily be wiped off.

The piston system was executed superbly.  Only the three pieces in the front two inches need to be removed for cleaning.  The piston regulator has four positions.  In the off position the action doesn’t cycle, essentially giving you a bolt-action gun.  The first position (smallest gas opening) is suited to use with silencers, which sustain more backpressure on the action.  The second position cycles the action reliably under normal conditions, and the largest opening can be used to compensate for weak ammunition, a very dirty gun, or other harsh conditions.

Shooting the gun for the first time was a pleasure.  There were absolutely no malfuctions.  Even after sustained firing the bolt was cool to the touch (though the barrel and gas vent area still got quite hot!).  Long-term reliability on a new design may not be certain, but the fact that Ruger is comfortable enough to roll these out in quantity is reassuring.  This should certainly outlast piston systems that use DGI bolt carriers with their separate gas key: The SR-556 carrier is machined from a single piece of steel with just a little hump over the main tube to take the impact of the piston.

Out of the box this is a very good gun, but it does have a few shortcomings:

  • Like all piston guns this is both front-heavy and heavier (just under 8 pounds) than comparable DGI AR-15s (typically closer to 7 pounds).  Of course even professional users of the DGI M4s have found it beneficial to put a vertical grip on the front of their guns.  I added a GripPod ($80 from Botach) and found this mitigates the imbalance nicely, in addition to deploying a handy bipod when desired.
  • The flash suppressor has uniform slots around its entire diameter.  When shooting prone or on a table this causes some of the muzzle blast to kick up dust.  Although closed-bottom flash suppressors require indexing to install, this should be a trivial factor to accommodate on a production line.  So shame on Ruger for not equipping this with a closed-bottom flash suppressor!
  • The telescoping buttstock is a standard M4 style, which leaves a lot of play between the stock and the buffer tube.  They should have just equipped it from the start with a Magpul CTR (shown in the photo above), for which I had to pay another $80. (To fit this gun be sure to get the mil-spec, not commercial size CTR!)
  • It doesn’t come with a front sling loop or swivel.

AR-15 with Trijicon ACOG and Gemtech M4-02 Suppressor

A free people ought not only to be armed and disciplined, but they should have sufficient arms and ammunition to maintain a status of independence from any who might attempt to abuse them, which would include their own government.  — George Washington

Bushmaster XM15-E2S with Trijicon ACOG TA01 and Gemtech M4-02 PiranhaIf the Founding Fathers, believing that every citizen should be armed to defend his life and liberty, were handing out guns today, every man would get an AR-15.  This is the American arm you can count on to protect your family, property, and fellow man.

The Rifle

There are a number of reputable manufacturers out there building AR-15 rifles to military specifications (the AR-15 is essentially a semi-auto-only version of the M16 infantry rifle), and there are many variations.  Since this is a tactical rifle I believe it should have a collapsible stock and the shortest legal barrel (unregistered), which is 16″: This makes it as easy as possible to store, carry, and use in close quarters if necessary.  If you start with those specifications then the biggest decision you have to make on the rifle is between a handle or flat-top upper.  I like my sights up high and I qualified on the M16-A2 while on active duty, so I went with the former.  There is more flexibility for modifications if you go with the latter.

The rifle itself will set you back about $900.  I bought one of the first available post-sunset (i.e., collapsible stock + flash suppressor + 30-round magazine) Bushmaster XM15’s for a total of $870 in 2004.  Since the standard grip is too small for my hands, I spent $20 to replace it.


The standard M16A2 sight system is very effective:  Using these sights at a long-range FrontSight course I was able to reliably hit man-sized targets at 400 yards from a kneeling position.

But the rifle is capable of more accuracy than you can achieve with iron sights, which is why this gun is not fully fleshed out until you have topped it with a 4x ACOG (Advanced Combat Optical Gunsight).  The Trijicon ACOG TA01 4x32mm scope is a standard military issue accessory.  And it is a beautiful piece of hardware: It produces a bright, clear image with good eye relief.  The reticle includes a bullet-drop compensator and is tritium-illuminated so that you can use it in dark conditions.  It mounts directly in the carry handle of an AR-15 using just one screw (and even leaves a hole through which you can still use the iron sights).  It is rugged, waterproof, and warrantied for life.  It is a perfect match for the .223 assault rifle.  But it is not cheap: I waited and managed to get one for $580 on Gunbroker.com, but unless you’re lucky you’ll probably have to pay at least $700 to pick one up new.


There are many options for suppressing this gun.  A lot of them are “quick-detach” cans, which can be installed with a single hand and a single twist onto a special flash hider, but these options generally cost at least $300 more than screw-on silencers.  Since it’s more hazardous to shoot a gun without a suppressor, I can’t think of a reason I would want to quickly remove mine, so I went with a screw-on can.  Since Gemtech has a good reputation and reasonable prices, I chose their $500 M4-02 “Piranha” model baffle suppressor.  It makes the rifle quiet enough to shoot without ear protection.  Though since the rifle shoots around 3000fps, it is by no means quiet: The sonic crack of the bullet makes roughly as much noise as a .22 being fired out of an unsuppressed gun.  But since that sound comes from the bullet’s shockwaves reflecting off of surfaces downrange it is much more subdued than if the shot were going off right by your ear.

Shooting an unsuppressed rifle — even one like the AR-15 with a reputation for very controlled recoil — is a violent experience.  In addition to the jarring recoil there’s a deafening report coupled with the palpable shock of propellant exploding from the muzzle.  Even with a good flash hider it can be disorienting.  Now putting this silencer on the end of the barrel absorbs practically all of the muzzle blast and a lot of the remaining recoil, making shooting almost … peaceful.  One drawback, other than the weight (a full pound for this particular can, protruding an extra 6″ beyond the end of the barrel), is the heat: After just ten successive shots the suppressor becomes too hot to hold with bare hands.  Keep shooting and it starts to radiate a heat mirage that can actually interfere with the sight picture if you’re trying to make a precise group.  (But it’s just doing its job: Here’s a good picture of a red-hot suppressor after hundreds of rounds of sustained, full-auto rifle fire.)


Guns rated for NATO 5.56mm also shoot .223 caliber ammunition.  (These have the same dimensions, but different pressure specifications.)  Since this is a standard military round it is both cheap and plentiful.  Right now you can find it in case lots for as little as $.20/round.  Most mil-spec ammo is 55gr FMJ, which leaves the muzzle of my 16″ barrel right about 3000fps.  I have also chronographed Georgia Arms’ 68gr match-grade BTHP at just over 2600fps.  Unfortunately, with all the ammunition I have tried I have never managed to shoot better than 3 MOA with this gun (that’s 1.5″ groups at 50 yards), though I don’t know if that’s typical.


You have to keep it clean.Field-stripped AR-15 The best critique of the AR-15 is a Mad Ogre classic (overboard, but they are fair complaints).  The biggest criticism can be summarized as, “The rifle defecates where it eats.”  This was due to a design trade-off (direct gas cycling) made to keep the rifle lighter and simpler.1 It results in a lot more carbon fouling in the action than you would get with a piston design.  But you don’t really have to spend 4 hours a day cleaning the gun to keep it from jamming.  (Unless you’re dragging it through mud and sand … in which case you’re probably a G.I. with four hours a day to spend cleaning it.)  In my experience if you field strip it and scrub it down with Breakfree CLP after every shooting trip it will continue to function reliably.

You will probably come across criticism of the 5.56mm cartridge.  A lot of people say you have no business putting anything smaller than 7.62mm in an assault rifle.  Again, this is a trade-off: 210 rounds of 5.56mm weigh the same as 70 rounds of 7.62mm; 7.62mm assault rifles have to be bigger and heavier to handle the larger rounds.  My reasoning: If you need to kill in one shot, and weight isn’t an issue, then use a sniper rifle.  To say that a gun doesn’t shoot the biggest round in existence is an observation, not a criticism.  (Moreover, for purposes of suppression the lower the bullet diameter the better.)


  • Light, standard weapon.  Everyone knows how to use it, fix it, and enhance it.
  • Light, cheap, plentiful ammunition.
  • Relatively easy to shoot accurately (for a large-capacity semi-auto rifle).
  • Military-spec, proven and durable design.


  • Soils itself.
  • Doesn’t operate well when not maintained.

In spite of these drawbacks, there’s a reason that this has been the standard U.S. infantry long arm for over forty years.  Every country that can afford to equip its soldiers with AR-15 variants does.  As far as I know this is still the best militia weapon you can buy: Any alternative will be heavier, less reliable, and/or more complicated.  If you need a light rifle for tactical operations — which includes the ability to easily carry and shoot a lot of rounds — then take an AR-15.

Continue reading