Love it or hate it, Pistol Caliber Carbines (PCCs) have quickly become a dominant force in competitive shooting.  USPSA, Steel Challenge, IDPA, and 3-Gun Nation all created new divisions in their respective games for PCC shooters in 2016, and the subsequent growth has been phenomenal.  In that time, two premium platforms have emerged as the preferred choice of PCC shooters – the JP Enterprises GMR-15 and the SIG MPX.  While the GMR-15 was purposely designed for competitive shooting, SIG had no idea when they designed the MPX in 2013 and brought it to market in 2016 what a hit it would be among competitive shooters.  The MPX was primarily designed for the military, police, and civilian markets as sort of a “next generation” H&K MP5 successor.  The advantage however that the MPX has is that it was designed from the ground up to be a piston driven PCC platform.  The GMR-15 suffers from the same inherent weakness of all blow-back AR-15’s – they’re based on a platform that was designed to run an entirely different caliber (5.56/2.23).

In mid-2016, SIG Sauer sent me an MPX Carbine for Test and Evaluation.  At the time, PCC’s were just starting to show up in small numbers at local matches – perhaps 1 or 2 at most.  And those folks that were showing up were often beating the pants off the other competitors.  Particularly in 3-Gun where, depending on the rule set, a PCC could theoretically be used in place of a rifle, pistol, or a shotgun (or all three) on many stages.  New rules were quickly added to level the playing field in 3-Gun, but PCC shooters very quickly earned the ire (envy?) of many 3-Gunners and became known as “cheaters.”  In USPSA competition, PCC shooters had similar advantages – particularly on stages which required the shooter to stand with their back toward the target.  That’s something easily done with a holstered pistol, but can’t be done safely with a PCC (because you’d be muzzling your squad members).  So PCC shooters always get to stand facing the targets on stages that require the pistol shooters to stand facing the opposite direction – a distinct advantage.  Admittedly, I was solidly in the camp of strongly disliking PCCs in competition…right up until the time that SIG sent me the MPX Carbine for T&E and I was instantly converted.  I’m now classified in PCC divisions in both USPSA and Steel Challenge and thoroughly enjoy shooting PCC.

I didn’t take SIG long to realize that they had a niche market with special requirements that required some special attention.  So it was not surprising that SIG, during the 2018 NRA Annual Meeting, announced they were bringing a version of the MPX to the market optimized for competition.  The new rifle would be called the MPX PCC (replacing the MPX Carbine in SIG’s civilian MPX product line) and I was among the first in the US to receive an example for Test and Evaluation in late November of 2018:

Specs

OPERATING SYSTEM:   Gas Piston
CALIBER:   9mm Luger
OVERALL LENGTH:  35.25 in (895 mm)
OVERALL WIDTH:  2.5 in (64 mm)
HEIGHT:  7.5 in (191 mm)
BARREL LENGTH:  16 in (406 mm)
WEIGHT : 6.63 lbs (3kg)
TWIST RATE:  1:10
MAG TYPE:  MPX
RETAIL PRICE: $2016.00
As an owner of the MPX Carbine, I’m in a unique position to directly compare the two models:
The above photo does a nice job of contrasting the changes made to the MPX PCC (top) relative to the MPX Carbine (bottom).
The overall barrel length (to include the muzzle device) has increased in the PCC.  The Carbine used a barrel that was about 14″ in length, but incorporated a pined and welded flash hider to get the overall length to the magic 16″ length to not be considered an SBR under Federal law.  The MPX PCC starts with an actual 16″ barrel, then adds a three-chamber compensator on the end of the barrel (intended to mitigate recoil).  Initially, I was not excited to see the additional barrel length – a shorter barrel is inherently easier to navigate around walls and ports found in most “run and gun” practical shooting sports, such as USPSA, IDPA, and 3-Gun.  But, I can understand why the decision was made – the pin and welded barrel on the older MPX Cabine isn’t exactly a flexible option for those who want the flexibility to add a different muzzle device.  Fortunately, most shooters will be using a rifle of similar length to the MPX PCC, so it’s not a competitive disadvantage.

THE GAS SYSTEM

Here’s where things get interesting.  According to the reps I work with inside of SIG Sauer, the gas system for the MPX PCC remains unchanged from the “Gen 2” MPX Carbine.  As it turns out, that may not be entirely accurate, according to the Robert Otte of In Lead We Trust.
Many were hoping SIG would go back to the Gen 1 MPX gas system, which had a less restrictive gas port, allowing the bolt to adequately cycle when using lighter loads typically found in competition.  According to Otte, the gas port on the Gen 1 MPX ranged in diameter from .0550″ and .0625″ depending on when it was made.  The Gen 2 gas port was more restrictive at .0469″  Otte found that the gas port on the example of the MPX PCC he received measured .0495″ in diameter – which puts it in between the Gen I and Gen 2 gas port size.  Otte also notes that there were some other significant changes to the bolt (redesigned) and the op rod.  The recoil springs also exhibit increased tension.  SIG also mentioned some minor changes to the bolt on the MPX PCC, adding that it was completely backward compatible as there are no changes in the receiver.
These changes should enhance reliability.  Some have reported online that the MPX requires diligent cleaning in order to run reliably.  In the two years that I’ve run my MPX Carbine in competition, I typically do a “light cleaning” (wipe down the bolt, interior receiver, and add more lubrication) after every outing and a “deep clean” (bolt disassembled, piston removed, etc.) about every 1000 rounds.  At about the 5000 round mark, I did have a piston related mechanical failure/breakage (which SIG repaired under warranty within 1 week) but outside of that, my rifle has always ran completely reliably.  That cleaning schedule really doesn’t vary much from how I maintain my direct impingement AR-15’s, so I don’t consider the MPX platform requiring undue care to be reliable and have been perfectly satisfied with the existing Gen 2 gas system.  But the changes Otte has noted are certainly welcome.
Perhaps the biggest improvement to the MPX PCC is the handguard/rail – it’s now M-LOK (vs. the old KeyMod system used on the MPX Carbine) and significantly smaller in diameter.  Typically PCC’s, as well as AR-15’s that are used in competition, have smaller-diameter handguard which makes driving the gun and transitioning between targets quickly easier to control.  Admittedly, I found the KeyMod handguard on the MPX Carbine unwieldy.  If you look in the photo above which shows both versions of the MPX together, you’ll see quite a bit more “daylight” coming through the PCC handguard than on the Carbine.  That’s because the M-LOK handguard has quite a bit less material, which translates to a significant weight reduction – 6.63 lbs. in the PCC vs. 7.6 lbs. in the Carbine.  Not only does the rifle feel significantly lighter, the balance feels much better, as nearly all that weight reduction is coming from the front end of the rifle.
The other big improvement on the MPX PCC is the trigger – SIG now puts a Timney trigger in the MPX PCC specifically designed for “longevity.”  PCCs and the MPX, in particular, are well-known for eating aftermarket triggers, so coming up with a robust trigger in the MPX PCC that is very important.  I attended the USPSA Area 5 PCC Championship earlier this year – the largest PCC competition ever held to date.  At this match I saw at least 3 guns go down in my squad alone, and at least a dozen others from other squads – mostly due to trigger breakage.  Given the challenges in keeping a PCC running during a high round count match, SIG’s choice of the Timney trigger is smart.  The trigger is certainly a quantum improvement over the awful Mil-Spec trigger that came in my MPX Carbine, but how does it compare to other aftermarket choices?  There are more choices for aftermarket competition triggers compatible with the MPX platform than I can count (because the MPX will work with most any trigger designed for an AR-15) but one of the most popular choices for competition has been the Hiperfire 24c (or the Hiperfire Competition as this model has been renamed).  I have the Hiperfire competition in my MPX Carbine and I absolutely love it.  After running the 24c in my MPX Carbine for about 5000 rounds, I became nervous about the trigger wearing out, and purchased the newer Hiperfire Competition and swapped out the 24c.  Neither has been unreliable for me but again, I did see Hiperfire triggers break in MPXs at the previously mentioned Area 5 match.  All this to say that the Timney MPX trigger certainly had a lot to live up to in my mind when comparing it to the Hiperfire triggers.  On paper, I wasn’t very enthusiastic.  The Timney trigger spec shows a 4.5 lb. pull weight, while both my Hiperfire triggers pull right at about 2 lbs.  When I first received the MPX PCC and dry fired the trigger, I noted how similar it was to the Hiperfire 24c/Competition – a flat-faced trigger with negligible (if any) take up, very crisp, clean break with an audible and tactile reset accompanied by almost no over-travel.  I also noted that the Timney trigger had a more positive reset, pushing the trigger finger back to the reset position.  In short, it had shooting characteristics almost identical to my beloved Hiperfire trigger, albeit heavier.  Here’s the 5-pull average on my Lyman Trigger Gauge:
The average was slightly below the stated 4.5 lb. specification, which did not disappoint me.  Dry firing the trigger made me a bit more optimistic about live fire testing, which I’ll discuss in more detail below.
In terms of other changes to the MPX PCC, it now ships with a five-position adjustable, folding stock.  Stocks, like triggers, are a very personal choice.  I’m not very picky in this regard and as can be seen in the above photos, I did fine with the collapsable stock on the previous MPX Carbine.  But the new stock definitely an improvement that most will find perfectly acceptable.  The new pistol grip is also slightly different – though no more or less suitable in my hand.

RANGE TESTING

When I brought the new MPX PCC out to the range for the first time and ran some drills, I was most curious about one thing – whether or not the new compensator would actually improve the shooting experience with the already ultra-mild shooting MPX.  Perhaps the biggest reason to choose the MPX over any number of blow-back AR-15 based PCCs is the soft recoil impulse of the piston-driven MPX.  Could a three-chamber comp improve on perfection?
The answer is an emphatic “yes.”  I ran factory 124gr. 9mm ammunition through both my MPX Carbine, and the new MPX PCC to best compare how the two rifles recoiled.  The difference in favor of the MPX PCC was indeed noticeable – perhaps a 20% improvement.  The MPX PCC shot “flatter” and more stable – very analogous to the difference between shooting factory ammo vs. hand-loaded ammunition that’s optimized for minimal recoil.    All well and good – but is there an actual improvement on the targets down range?
To test this I ran one 30 round magazine through both the MPX Carbine and the MPX PCC doing a basic drill.  Starting with two side-by-side targets at a distance of 10 yards and from a standard USPSA-style “stock on belt” start, on the beep I fired two rounds on the left target, and two on the right at my “100%” speed.  This gave me about 7 runs with each rifle. I compared both my times on the shot timer, and the shot groups on each target.
The times we very, very similar, with my fastest time (pictured above) coming from the MPX PCC.  What was noticeably different were my shot groups – I shot all “As” with just one “C” on each side with the MPX PCC.  My hits were not as well grouped (particularly on the left side target) using the MPX Carbine.  I re-ran the drill a few times, each time favoring the new MPX PCC – primarily due to the comp, but perhaps also due to the rifle being a bit more controlable with the thinner handguard.  Running the drills also made me realize that as much I consider the Hiperfire Competition my favorite trigger, I wouldn’t need or want to replace the Timney trigger that comes with the MPX PCC.  2-3 lbs. of pull-weight might make a significant difference in a handgun, but with the three points of contact a rifle provides, the weight difference is far less significant and hardly noticable when shooting at speed.  Again, the target doesn’t lie – my accuracy was considerably better with the Timney trigger equipped MPX PCC vs. my Hiperfire trigger equipped MPX Carbine .  Clearly the trigger did not detract from my performance.  Between that, and the fact that the Timney MPX trigger is specifically engineered for the MPX to be long-lasting and reliable, and the fact that it would cost another ~$200.00 to buy a Hiperfire Competition trigger, the choice to keep the Timney is an easy one.
After running about 500 rounds of various makers and bullet weights through the SIG MPX PCC in various drills (100% reliable), I feel confident in saying that SIG has created the nicest out-of-the-box competition PCC available on the market.  You can literally take this rifle, slap on your choice of red dot optic (mine is the SIG Romeo 3), zero it, and head to a match and be completely competitive with any other PCC at the match.  The new, thinner handguard is a dream to use, and the rifle feels impossibly light and maneuverable.  The piston-driven MPX is already well known for being light years ahead of any blow-back PCC in terms of how softly it shoots, with remarkably little muzzle movement.  With the addition of the three-chamber compensator on the MPX PCC, it quite honestly shoots like a rimfire rifle.  I don’t think you can find flatter, more pleasant shooting PCC on the market.
SIG didn’t raise the retail price ($2016.00) from the previous MPX Carbine, but the MPX PCC brings much more value to the table (the trigger alone is worth $200 more than the Mil-Spec trigger on the MPX Carbine).  I’m already seeing street prices of $1700.00 for the MPX PCC.  That’s a steep price tag for sure, but consider that the BASE price (with no customization) of a JP Enterprises GMR-15 is $1699.00.  The GMR-15 is certainly a nice, ultra-reliable PCC (and the only model I consider a realistic direct competitor to the MPX) but it’s a blow-back rifle that it at least 2 lbs. heavier than the MPX PCC.
The only modification I’ve made to my MPX PCC is to add the Taran Tactical Innovations magwell to the rifle, and their mag extensions to my MPX magazines.  Look for me shooting the MPX PCC at matches in 2019 and beyond.

About John B. Holbrook, II
John B. Holbrook, II is a freelance writer, photographer, and author of ThruMyLens.org, as well as LuxuryTyme.com and TheSeamasterReferencePage.com. *All text and images contained in this web site are the original work of the author, John B. Holbrook, II and are copyright protected. Use of any of the information or images without the permission of the author is prohibited.

Facebook  • Twitter • Youtube • 

No related content found.