The Ultimate Firearms Destination for the Gun Lifestyle

SIG’s Civilian-Legal Shorty

The MPX K Might Be a Perfect Traveling Partner

Photos by Straight 8

Elsewhere in this issue, Matt Jacques discusses the merits of the modern-day coach gun and the historical precedent behind it. We probably don’t need to persuade many road warriors that having a little extra ballistic capability on hand isn’t a bad thing — after all, we carry handguns not because they’re the hammer of Thor, but because they’re the most capable firearm that’ll fit in a waistband.

When it comes to commonly available guns, there’s a sliding scale of size and effectiveness, ranging from the pocket .380 on one hand, to the 7.62 NATO battle rifle on the other. SIG’s MPX K is a specialized tool that lies somewhere in the middle of that continuum, giving the user a means to accurately deliver 30 rounds of 9mm from a package about the same size as the laptop this story was written on.

Due to the idiocies of the National Firearms Act, those looking to bridge a capability gap between handgun and rifle are saddled with restrictions that make zero sense. Even after filing the necessary paperwork, paying a $200 tax, jumping through hoops, and waiting up to a year for permission to cut down the barrel on a rifle, should you then wish to take your gat while you exercise your First Amendment right of freedom of association and visit your family in another state, you’ll first need to file a “Mother, may I?” letter with the ATF, or else fall foul of the law. Note that ATF form 5320-20 doesn’t apply to suppressors, for which we can all be grateful, and is usually approved in less than two weeks; but we’ve yet to see any evidence that its completion or lack thereof has made a significant impact on criminality in the 83 years since the requirement was imposed. I’ll take, “Bullsh*t government paperwork” for 500, Alex.

SIG MPX arm brace sig sauer mpx parts

Since the advent of the SB Tactical pistol brace and the most recent BATFE opinion letter on the subject, SBR restrictions have become somewhat moot. RECOIL contributor and noted 2A legal authority Adam Kraut addressed the ramifications of this decision in a recent online article on Bottom line — if a pistol comes from the factory with a brace installed, then making a case that the owner illegally manufactured a short-barreled rifle through the act of touching their shoulder with the brace is a hard row to hoe. In the eyes of the law, it’s a Title 1 firearm, and thus no permission slip is needed to cross state lines. Which brings us to the glorious, though seemingly random collection of letters that is the MPX K PSB, seemingly less the nomenclature for a gun than a bad Scrabble hand.

A couple of years back, we got our paws on one of the very first MPX variants to leave SIG’s Exeter, New Hampshire, plant and were so impressed that we immediately filed a Form 1 to SBR it. It’s since become one of our go-to guns when introducing new shooters to the joys of this lifestyle. Without fail, everyone who shoots the 9-inch-barreled carbine winds up dumping rounds as fast as they can pull the trigger. Its lack of recoil and muzzle blast makes it one of the most user-friendly semi-autos on the market, traits accentuated by its gas operated, rather than blowback, bolt. While AR-pattern pistol-caliber carbines have come a long way in the past decade, they’re still hamstrung by their operating system, which produces more felt recoil than that of either the MPX or the HK MP5 it was designed to supplant.

Due to its stubby, 4.5-inch-long tube, we’d be hesitant to put the K version in the hands of a newbie — we’ve witnessed one experienced competitive shooter put a round through their mitt when running an MP5 at a match, as they attempted to shoot it a la Costa. Although that was a self-correcting mistake, for a while there it put a damper on things. No, this gun is best suited to someone with more time behind the trigger. While it’s still fun to shoot, it’s considerably harder to run than a 16-inch carbine, demanding more care and attention. Once that caveat is embraced, it’s a contender for the Ultimate Truck Gun Championship, a title fight that should be announced in the same tones reserved for monster truck derbies.

sig sauer mpx

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