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Review of the SIG Sauer MPX K Pistol


Followers of ThruMyLens know I’m a big fan of shooting Pistol Caliber Carbine – PCC.  I acquired a SIG MPX Carbine in the fall of 2016, and immediately started shooting it in both 3-Gun and USPSA.  This year, I shot even more PCC, and added Steel Challenge to the shooting disciplines I enjoy.  I won most of the local Steel Challenge competitions in which I shot in the PCC division, and went on to shoot in the Kentucky State Steel Challenge Championship where I won my class.  I would finish 2017 as an “A” class shooter in the PCC division.  Having trained with and shot the MPX so much during the last year in competition, I really gained an appreciation for the MPX and saw it’s potential a highly effective home defense weapon – perhaps even more so than an AR-15 chambered in .223/5.56.  I made the decision to acquire a 2nd SIG MPX, and configure it for an optimal home defense weapon.  I chose the 4.5″ barrel MPX K Pistol:

Stock photo from

I’ve had several firearms training classes which dealt with room clearing – something I would choose to avoid in a home defense scenario if at all possible.  When clearing a room or manuvering in a house, a shorter barreled weapon is much prefered over a traditional 16″ rifle barrel.  A 16″ barrel is much easier for a home invader to grab onto as well as being more difficult manuver in tight spaces.  Using a handgun in these situations mitigates the inherent disadvantages of a 16″ barrel, but also looses the advantages a rifle brings in terms of shot placement accuracy, and magazine capacity.  Neither solution (handgun, 16″ barrel rifle) is ideal for home defense.  So I decided to get my home defense MPX configured as a “pistol” as defined by US Burea of Alcohol, Tabaco, and Firearms (ATF):

A firearm, as defined by 26 U.S.C. 5845(a)(4), is made when a handgun or other weapon with an overall length of less than 26 inches, or a barrel or barrels of less than 16 inches in length, is assembled or produced from a weapon originally assembled or produced only as a rifle.

Additionaly, I decided that I would attached to my MPX pistol the SIG folding brace.  There’s been some confusion with regard to how the ATF views Pistol Stabilizing Brace devices (PSBs) but as SIG prominantly states on their website, the ATF issued a clarifying letter in April of 2017.  Attaching a PSB to a legal pistol does not make it a “rifle” nor does shouldering a pistol with a PSB.  At some point I may seek to go through the National Firearms Act (NFA) process of converting my pistol to a short barrel rifle (SBR), but I wanted to start with it classified as a pistol in case I didn’t like what I ended up with and wanted to legally sell the pistol to someone else – something that’s far easier to do if the firearm is considered a legal pistol by the ATF, and not an NFA SBR.  I attached the SIG folding brace and an InForce weapon light to my MPX pistol, and mounted an Aimpoint T2 red dot optic with a LaRue Tactical quick detach mount.  Additionally, I changed  out the stock SIG charging handle for a Radian Arms MPX charging handle (which I’ve come to love on my MPX carbine) and I took out the stock trigger and replaced it with a Hiperfire 24E.  Here’s the finaly product:


You’ll note there aren’t any backup iron sites on my MPX pistol.  That’s because SIG stopped including them on the MPX.  So I have another set ordered from SIG, which added about $70.00 to the cost of my project.  Shame on SIG for not including them as they did with the MPX carbine I purchased last year.

Outside of having to order backup iron sites from SIG, the project has come out absolutely perfect.  I’ve essentially got a home defense version of the weapon that I shoot in competition.  This isn’t a cheap option however and what I’ve done to date comes in at right about $2500.00.  The SIG MPX is a premium priced weapon relative to other options, but I feel it’s worth the asking price.  When I took it out on the range, I was pleasantly surprised – I wasn’t sure how the 4.5″ barrel would affect felt recoil.  But after firing a few hundred rounds, I really couldn’t tell much difference recoil-wise between this K pistol and my 16″ carbine length MPX.  It shoots extrordinarily flat with less muzzle rise than even my competition AR-15s which have compensators and adjustable gas blocks.  That makes the MPX a weapon I or my wife can easily and comfortably use in a home defense secenario.  Again, the weapon was configured to be a close quarters home defense gun, but I didn’t have any problem shooting it at 50 yards when I zeroed the optic.

I chose the folding SIG brace due to how incredibly compact the package is when the brace is folded – you can easily fit this weapon into a small backpack.  That greatly increases the utility of this MPX and makes it a via option when I travel.

Because of the incredible growth of PCC in competetive shooting, and the fact that the SIG MPX has emerged to become one of the prefered platforms for competitive PCC, it’s easy to forget that the MPX wasn’t originally designed to be a “gamer gun.”  Rather, it was designed to be a small, lightweight personal defense weapon for military and law enforcement – many considered it to be something of a successor to the famous HK MP5.  Utilizing an MP5-like piston gas system, the MPX has both incredible reliability and an impressibely pleasant recoil impulse.  Yes, the MPX is fun to play with in competition, but it definitely excels as a defensive weapon and I’m extemely pleased with how my project has turned out…so far.  The next step for my home defense MPX will be to dive head first into NFA territory and acquire my first suppressor.  Suppressing my MPX will truely make it an ideal home defense weapon.  So stay tuned for my next article which will detail my experiences in going through the NFA application process for the first time.

About John B. Holbrook, II
John B. Holbrook, II is a freelance writer, photographer, and author of, as well as and *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.

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