SIG Sauer MPX RMPX-16B-9-35 9mm Luger

Pistol Caliber Carbines are the latest rage for action shooting sports and self-defense classes —and why not? They can weigh less, recoil less, and cost less to shoot than their centerfire rifle brethren. But as current as the concept seems, it is not exactly a new idea. History tells us that Colt Firearms finally agreed to chamber is Single Action Army pistols in 44 WCF (also known as the 44-40) in 1877. This was a major step for the company since they had refused to offer their pistols in anything except 45 Colt to that point. That concession allowed Colt’s customers (about half the cowboys in the American West) to carry a single cartridge that would fit their pistol and their 1873 Winchester rifle. This meant they could carry one type of ammo that could be used in their revolver for close-range work and the same round in a short-barreled rifle, bringing them more capacity, greater range, and better accuracy.

In today’s marketplace, when 223 Remington and 308 Winchester rounds are more available than a couple of years ago but are still expensive, the 9mm Luger appears to be the cartridge de jure. Having seemingly won the pistol caliber wars over the 45 ACP, the 9mm is the most popular centerfire cartridge in America today by a substantial margin and still growing. Our search for less-expensive training and competition options led us to three 9mm Pistol Caliber Carbines, each of which filled a slightly different niche.

Our first test piece is the new FPC (Folding Pistol Carbine) from Smith & Wesson. It is a lightweight break-action that we are seeing sell for under $600. The next is the brand-new Saint Victor Carbine from Springfield Armory. Based on a simplified straight-blowback action, we’ve found this PCC for a little over a grand. Our last sample is the MPX from SIG Sauer in a variant built to be competitive right out of the box for USPSA PCC division. Cost for all those bells and whistles is around $2000.

The United States Practical Shooting Association (USPSA) has been one of the primary driving forces in action pistol competition for well over 40 years now. Once almost exclusively the purview of shooters using large-caliber single-stack semi-autos, USPSA has diversified. Growing from two recognized divisions with specialized equipment allowed, there are currently eight certified divisions and a ninth provisional category being tested. The last two formally accepted divisions (Carry Optics and Pistol Caliber Carbine) are hot right now, and both offer some of the same advantages: lighter-recoiling chamberings (almost always 9mm), larger magazine capacities, and optical sights. All that means is that the pistols and PCCs are relatively easy to shoot, comfortable to shoot, and forgiving to those with less than eagle eyes.

Competition is a demanding taskmaster. What doesn’t work is changed or forgotten quickly and SIG Sauer has been in the forefront of these two divisions. Of course, it doesn’t hurt that they have Max Michel and Lena Miculek shooting for them and telling them what works. The SIG P320X and Legion series pistols have been a huge success for SIG in both the Production and Carry Optics Division. Likewise, the MPX pistol-caliber carbine has done the same for the PCC Division. So we were interested in seeing how the more-mature MPX platform set the tone for new pistol-caliber carbines from S&W and Springfield Armory.

To help us get the best out of the carbines, we attached a Holosun AEMS (Advanced Enclosed Micro Sight), which runs about $400 from Brownells.com. Because this test group lives in a mostly green world, we chose the red-dot option over the green. This version provides a 32-minute-of-angle (moa) circle around a 2-moa dot. Not only does the AEMS come with an expected battery life of up to 50,000 hours, the battery compartment opens from the side for easy power replacement, and the sight has a solar back up. Add in the aluminum housing along with the flip-down lens cover, and we found this to be a very sturdy sight. Here’s how the rifles performed.

SIG Sauer MPX RMPX-16B-9-35 9mm Luger

$2000

GUN TESTS GRADE: B+

Designed specifically for USPSA-type competition, the MPX is just about ready to go to the match straight out of the box. With the short-stroke gas-piston design, recoil was the softest of the PCCs tested. We loved all the bells and whistles, but we were a bit disappointed by its accuracy. The price tag is an eye-opener.

Now in its (at least) 2nd generation, the SIG MPX is built for the speed necessary to win matches. The company reduced the weight from the Gen 1, leaving a more slender fore end made of aluminum and a ton of lightening cuts. That made it easier to swing and stop, while moving the balance point back toward the shooter. A thin 16-inch barrel is now crowned by an effective three-port compensator. SOP for competitors shooting non-compensated pistols in the past has been to load a heavy bullet with a fast powder. This produces the least muzzle flip and lowers the time needed to shoot a course of fire. With a compensator, try lighter-weight bullets going fast. That increases the gas pressure and makes the compensator work more efficiently. 

The operating system isn’t new for this model, but it is part of the solution. The MPX utilizes a short-stroke gas piston. Unlike the straight-blowback system in our other two test pieces, a gas-piston system allows the MPX to use a much lighter-weight bolt and bolt-carrier group. With less reciprocating mass, the recoil impulse is softer, meaning, normally the MPX would come down out of recoil faster and ready for follow-up shots. Technique and soft-recoiling 9mm rounds can obviate some of that advantage. Note that the Springfield was actually slightly faster than the MPX. We would hate to have to live on the difference, though.

Competition firearms need to have controls that are ergonomic and intuitive to control. The MPX provides a truly ambidextrous thumb safety, bolt release, and magazine release. One of the signs of consumer acceptance is the selection of aftermarket parts. The logistical tail on the MPX is huge, and we used it to correct a problem we have. We’ve commented before that several testers in this group have less than basketball-player-length fingers. The mag release on the MPX (a loaner from one of our testers) was a bit difficult for us to operate without shifting the gun, which we don’t like to do on this platform. Odin Works (Odinworks.com) had an easy solution in the guise of an extension. Easy install. Problem fixed.

The trigger, which was problematic in Gen 1, has been replaced by a superb Timney unit. Required compression across 10 measurements with a Lyman digital trigger gauge showed an average 2.4-pound pull with a standard deviation of only 5 ounces. Also updated from Gen 1, SIG Sauer flared the magazine well, making reloads easier and quicker.

Those familiar with Modern Sporting Rifles will note similarities and differences in the MPX takedown procedure. The front and rear pin are in the same places we would expect. With an empty chamber and the magazine out of the gun, slide the rear pin to the right, tilt the upper assembly forward, and pull on the charging handle. There things start to differ. The bolt, carrier group, and recoil springs are a single captive unit that come out with the charging handle. Removing the springs from the carrier took us a couple of extra seconds until we read the manual. Complete instructions are also available for removing and cleaning the gas piston. We did that once and haven’t felt the need to do so again. There isn’t any buffer, buffer tube, or long recoil spring. All the moving parts end at the back of the receiver. This allowed SIG to put a vertical section of pic rail on the aft end of the receiver. Then they attached a sturdy folding stock to the rail. Pushing down on the top of the hinge with your thumb while lifting up on the buttstock with your fingers unlocks the buttstock and allows it to fold to the left. Yep, it can be fired while in that position. A single quick-detach point is located at the rear of the receiver below the hinge.

Our Team Said: We’ve had the chance to work with the MPX a little longer than the other two PCCs in this test. To date, we have more than 1000 rounds through this carbine and have not had a single malfunction. We have been able to use it in a couple of USPSA matches where it was fast and soft. Still, we were a bit disappointed in the shooting results. None of the PCCs liked the 147-grain handload, which has been our bread and butter in matches for years. The SIG did well with the other ammo, but not as well as the S&W and, especially, the Springfield. Maybe we just haven’t found the magic ammo for the MPX yet.

Written and photographed by Joe Woolley, using evaluations from Gun Tests Team members. GT