Even in the rain, the SIG MCX Regulator ran like a champ, and the optics made it easy. (Photo Provided by Author.)
January 30, 2025
By Patrick Sweeney
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There are people who live in states where some particular firearm details are not permitted. I know, I know, but there it is. (One such person I know is the fourth generation of six on the family farm. He and the family can’t move the farm, so he stays.) What to do? Simple: ring up SIG SAUER and get an MCX Regulator. Regulator? Yes, the SIG that looks like a ranch rifle.
The Regulator is a gas-operated self-loading rifle that lacks a pistol grip. In particular, it is the MCX piston-driven upper, on a lower receiver machined to accept a Magpul stock, and the combination is one that works like a champ. OK, the elements in this package:
Breakdown of the MCX The upper is a standard MCX upper, with the system driven by a piston. The gas block has an adjustment, so you can regulate the gas flow to deal with a suppressor. (I have to figure the locations where a pistol grip is verboten, but a suppressor is okay are limited, but who knows.) The SIG barrel, sixteen inches long and with a 1:7 twist rate, is hammer forged and given a nitride surface treatment. It has the gas block permanently attached. If you want to go and swap barrels (why?) you will be swapping the barrel and gas block. I don’t see that happening until you’ve shot the bore out, which will be a good, long, time. The Regulator arrived here (and they all do) with a muzzle brake installed. If you want something else, just unscrew it and attach the device of your desire.
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The SIG MCX Regulator, on the right side. Wait, where’s the pistol grip? There isn’t one, that’s the big deal. On the left side, the Regulator shows the MCX DNA it has, plus the well-designed fit to the Magpul stock. (Photo Provided by Author.) Keeping your hands off of the hot barrel, and providing plenty of places to add accessories, SIG includes a lightweight, free-float handguard on the Regulator. This is the regular MCX handguard, and it is a good one. I count 25 MLOK slots where you can mount things, at the 3, 6, and 9 o’clock positions, plus the flats in-between. There are four more above the 3 and 9 o’clock rows, so if you can’t find a location to mount your light, laser, sling or cup holder, don’t blame SIG. On top, the handguard rail is contiguous with the receiver rail, so anything you mount up there is on a single plane.
So, back-up iron sights (BUIS), one of my must-haves, optics, laser designator, thermals or night vision, there’s plenty of room there as well. In fact, there might be too much room, as you could easily double the weight of the Regulator by over-enthusiastically mounting gear. Again, don’t blame SIG. If you ever need access to the barrel, gas block, or to do a swap, the handguard is held in place by means of four bolts, one on each side and two underneath, just forward of the upper receiver.
The lower is an interesting piece of modern sculpture. While it follows the layout of your vanilla-plain AR-15, the contours and angles are different. And better. The magazine well is beveled for fast and easy reloads. The controls: bolt hold open and release, mag catch and safety, are ambidextrous. (Excuse me, bilaterally symmetric.) The safety is an interesting change SIG has made from the AR. Since there is not a pistol grip (we’ll get to that) the regular location and direction of movement of the AR selector wouldn’t work on the Regulator.
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The ambi controls are clear. The safety is worked by your trigger finger, and the tab under the ejection deflector is the bolt release. (Photo Provided by Author.) So, SIG went and changed that. Instead of being worked by your thumb, the selector is worked by your trigger finger. (Or, at least by mine. It works great.) It is shielded by the contour of the rear part of the lower receiver, so it won’t get inadvertently brushed on or off. The left side mag release and bolt hold-open are what you’d expect, but you might have to search to find the right-side bolt release. It is a small black steel tab lurking underneath the brass deflector. The deflector is not an integral part of the upper, but instead is a bolted-on part. I can see the attraction of this approach, as it allows for changing deflectors with caliber changes (if needed) and also offers options in size and angle. (Again, if needed.)
Inside the lower, SIG installs their two-stage trigger, which gives you an excellent trigger pull, and you do not have to do any parts swapping to get that great trigger pull. (Keep that, and other details in mind when you consider the price.)
In the back of all this is the lower receiver hump, where the stock is attached. SIG has chosen (and wisely) to use a Magpul stock here, the Mossberg-pattern stock. So, you get the great grip angle, built-in sling slot, and replaceable cheekpiece and buttpads, to adjust comb height and length of pull. The Magpul stock has no ability to handle a buffer tube, nor any other kind of in-the-stock recoil spring design, such as us old-timers might recall from the Remington 1100 or FN-FAL. So how does SIG do it? Remember, this is the MCX Regulator, so the upper uses a standard MCX design, with its own dual-spring recoil system contained entirely in the upper receiver. It is charged by means of a charging handle on the top center of the upper receiver, just like an AR-15.
A regular-style charging handle to get things going.(Photo Provided by Author.) That means you can, if you wish, swap your Regulator upper onto a standard MCX lower, and vice-versa. The Regulator is currently offered in 5.56 and 7.62x39, so if you have an MCX in those, you can swap uppers back and forth. (Remember, if one of them happens to be an SBR, you can’t do this swap. The shorty barrel upper has to stay on the serialed-SBR lower. Just reminding you, that’s all.) And, with the SIG adapter kit, you can put the MCX upper (Regulator or not) onto a standard AR-15 lower. So, if/when you do finally move out of your restricted area, you can move your upper to a new lower. The exterior is done up in FDE, but not just any FDE. It is a special formulation of Cerakote that reduces IR signature (it is now in the second generation of formulation) so it not only looks good, but it also offers reduced attention-getting IR reflectivity.
Taking the SIG MCX Regulator apart is just like taking apart any AR-15 or MCX. Nothing new here. (Photo Provided by Author.) Now, in looking over the specs I noticed that the Regulator is listed as being just under eight pounds. The racks of your local gun shops are filled with AR-15s that are just under eight, and a lot of them closer to seven pounds. However, the unavoidable design consideration of making the lower rear hump a socket the Magpul stock can fit onto means it has to weigh a few ounces more than a vanilla-plain AR-15. I knew that when I opened the box, but my first impression as “Why does this thing weigh so much?” I’ll admit I was a bit low on coffee that morning, because it took me a few moments to realize why.
When you add a first-class set of optics, in 30mm tube with illumination, in hell-for-tough steel mount and rings, you’re going to add weight. The Tango6T adds 22 ounces all by itself, and the mount has to be another six or so. If you add a sling and a loaded magazine of ten rounds (the Regulator takes regular AR mags, so capacity is up to you and your local laws) you’re going to be over nine pounds full-up. A nine-pound AR-15 or any rifle in 5.56, is not going to recoil with much oomph, and the muzzle brake on the barrel takes care of the rest. In bench-testing it to get a quick check of the zero, I could see bullet impacts though the scope at the 100-yard berm.
The gas block and the gas flow regulator in case you want to mount a suppressor to your Regulator. (Photo Provided by Author.) Oh, and that brake? It works, and it is flashy as well. It was a cold, overcast and rainy day, and I could see flash in the scope on each shot with some loads. Were I keeping this one in the inventory, I’d swap the brake for a flash hider and call it good.
Now, the MCX Regulator is a fine rifle, but what’s it for? Clearly, it fills a niche for those living in restricted states. But it also satisfies a need for those who might not be in restrictive states. The AR-15, the MSR, is a capable and versatile rifle, but what it isn’t is sleek. If you want to transport your rifle on a four-wheeler in a scabbard, an AR-15 kinda sucks. In fact, “AR-15” and “scabbard’ is a combo like socks on a rooster, but the MCX Regulator slides right into a properly-sized scabbard — I can see accessory makers already planning just that.
Accuracy Not surprisingly, the MCX Regulator showed a preference for some ammo over others. All rifles do, you have to find what yours like.(Photo Provided by Author.) Then there’s the matter of caliber. Another 5.56? Ok. One in 7.62x39? I guess, although I’d much prefer it in .300 Blackout. (You can swap an MCX upper in .300 just fine.) SIG tells me that MCX Regulator can be built in other calibers, but they are not planning any at this time. Well, the Regulator, in one of the straight-wall cartridges, for hunting, would be like crème brulee after a fine meal: just the thing. For those who have to use straight-wall cartridges, and even those who don’t but like the ballistics, an MCX Regulator in .350 Legend, .400 Legend, or .450 Bushmaster would be a whitetail harvester par excellence. A simple barrel swap would be all it would take, although I can see the SIG engineers spending a lot of time fussing over the piston system to make it just right. Until then, the Regulator in 5.56 is a great rifle and a lot of fun to shoot. And in 7.62x39 is certainly up to the task of bringing home the venison.
Does the MCX Regulator shoot? Bears/woods? Pope/Catholic? Are you surprised? You should not be, SIG makes superb rifles. (Photo Provided by Author.) Now, the cost. The list price of the MCX Regulator is $3,278, but I’ve seen them for an even three grand . The Tango6T is listed at $2,200, but I’ve seen them as low as $1,800. The mount is $130, but you can probably score yours for an even Benjamin. On paper, that’s $5,600, but for the accuracy, the reliability (I had no failures) and the looks, pretty good. And add all that to being permitted in places a regular AR-15 wouldn’t be, and you’re doing just fine. Quality, status, and pride of ownership costs money. For once in your life, treat yourself.
(Data Provided by Author.) SIG SAUER MCX REGULATOR SPECS Type : Hammer-fired semi-automaticCaliber : 5.56 (also avail. in 7.62x39)Capacity : 10+1 rounds (any standard AR-15 magazine)Barrel : 16 in.Overall Length : 39 in.Weight : 7 lbs. 13 oz.Finish : FDE CerakoteGrips : n/aSights : n/aTrigger : 3 lbs. 1 oz.MSRP : $3,279.99Contact : SigSauer.com