The movement of the piston is the control (and the adjustable throttle, more on that in a bit) and is what regulates the transfer rod movement. Only so much gas can go through the gas port and drive the piston, and excess pressure simply drives the piston harder, but not all of that excess is delivered to the transfer rod. But, we’re getting a bit ahead of ourselves, so let’s start from the beginning.
Once you get past all the “whose design did they use?” nonsense, you get to enjoy the wonder that is a Ruger offering in this day and age. The box itself is a cardboard carton with “SR-556” and the Ruger logo printed on it. I suspect in 50 years (assuming we still have guns, or a civilization) that the cardboard box itself will be a hot item in the collector’s market, since most users will simply toss it.
Inside that is a relatively discreet rifle carrying case in black synthetic cloth, with the Ruger logo and name bonded to it, in red. The rifle itself comes with three Magpul PMag30 magazines, black windowless, a set of rail covers, an owners manual, and the Federally-mandated lock. (I sometimes wonder which of our legislators had a family business in the lock industry.) There’s no cleaning kit and no sling, which is fine by me. I have a box full of factory-supplied cleaning kits and slings (and padlocks) that I never have a need for, so leaving them out doesn’t hurt me in any way. But if you were expecting a cleaning kit or sling and don’t currently have one of either, you’ll have to buy one of those on your own.
The rifle itself? Oh, boy. The lower is a small-pin (there had been some early rumors that Ruger had used the same large-diameter hammer and trigger pins that Colt used for a couple of decades. Wishful internet rumor-mongering, I’m glad to tell you) mil-spec lower marked “safe” and “fire” that, were it not marked with the Ruger lower, would not be distinguishable from any of the host of other mil-spec built semi-auto lowers. It has a Hogue rubber pistol grip with the Ruger logo in it and a six-position telestock with the Ruger logo moulded into it. The safety is not ambidextrous, and the trigger pull is a thoroughly acceptable mil-spec trigger pull.
That is, it is creepy, gritty, and a bit on the heavy side as it comes out of the box. And, just like all the other milspec triggers I’ve ever used, I expect it to improve a great deal with a little bit of dry-firing and use. Ruger has had a reputation for some time of providing “lawyer-proof” triggers on their products. Maybe yes, maybe no, but in this instance we can lay the trigger at the feet of the government. That is, mil-spec.
As plain, ordinary and unremarkable as the lower is, the upper is where all the action is.
First, the upper receiver is a flat-top, machined from a forging, complete with forward assist and ejector lump. The railed, free-float handguards are made by Troy Industries, and they’re marked with the Ruger name and logo. There is another interesting detail to them: they are secured to the upper. There are a pair of roll pins in the upper, one on either side of the joint between the receiver and the handguards at the top, and a single, much bigger one on the bottom.
Clearly, they pin the two together, a good idea with a piston system running in between. The handguards are surmounted by a set of Troy sights, both folding, front and rear. While made by Troy, they are marked with the Ruger name and logo. While Ruger has outsourced primo parts on the items they themselves do not make, they want to make it absolutely clear just whose rifle this is. (And it isn’t your Father’s Buick, for those who remember the old ad campaign.)
The gas block is pinned to the barrel, and the gas regulator is adjustable. It has four settings, from “0” to “3,” and is meant to be self-regulating. Zero means no gas, so if you want to use your SR556 as a straight-pull bolt action rifle, go for it. The other three are increasing amounts of gas. The “1” setting is not meant as a suppressor setting, per se; it just delivers less gas. And the “3” setting is just more gas. Ruger recommends that you not use a setting any higher than needed to run reliably with the ammo you’ve selected. (Factory-new, no reloads, thankyouverymuch.) Those lucky enough to have suppressors will probably run the Ruger on the “1” setting when they have the can installed.
Ruger recommends that ejection be directly out to the side, that is, ninety degrees to the direction you are firing. If it is “late” (Ruger’s term, not mine, nor a common description for ejection) and throws the empties to the rear, increase gas port size/number and keep shooting. If it is “early” (again, Ruger’s term) with brass going forward, turn the gas port/number to a smaller setting. My bet is that since Ruger ships it with the regulator set at “2” and most ammo will work just fine that way, that we’ll see lots of SR-556 rifles with the regulator frozen at “2” after hundreds or thousands of rounds fired.
Most shooters will fire a few rounds, see that the brass is exiting the area with sufficient alacrity and enthusiasm, and ignore the regulator afterwards. And, most shooters being most shooters, they won’t go and wrestle the gas system apart after the first shooting and cleaning session. In a few years, I’d expect gunsmiths to start seeing Ruger SR-556 rifles with carbon-welded gas plugs in place, looking to have them removed for cleaning.
This article is an excerpt from the Gun Digest Book of the AR-15, Vol. 3. Click here to get your copy.
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