The “Reverse Stretch” MP-5K PDW: Improving on Perfection
By Will Dabbs, MD
Photos by Sarah Dabbs

The capacity of Americans to tinker with stuff at times boggles the mind. Market-driven adaptations for cars, computers, and all manner of consumer trinkets continuously redefine the state of the art. Nowhere is this more blatantly manifested than in the U.S. firearms market.

Take a look at the Saiga 12. The Saiga is itself a 12 gauge adaptation of the venerable Kalashnikov rifle system. In its stock form imported from Russia the Saiga is an intriguing yet fairly pedestrian rendition of the original that is sadly castrated to meet U.S. import guidelines. Six months after it hit our shores, however, enterprising entrepreneurs had begun dreaming up widgets and ditzels to transform the modest Saiga 12 into a zombie-slaying Ninja machine. The explosion of accessories and bling continues apace to this day.

The Machinenpistole 5 began life as the HK-54 in Heckler and Koch’s promotional literature. Adapted from the roller-locked G-3 battle rifle that was itself an evolutionary development of the wartime STG-45, Great 03, and MG-42 belt fed machine gun, the MP-5 set a standard for controllability and reliability in 9mm submachine guns that has yet to be bested. When news footage of black-clad SAS troopers armed with MP-5’s storming Princess Gate in London in 1981 splashed across every television screen on the planet, HK’s marketeers must have just grinned.

Soon every tactical team in the world had to have black fatigues and MP-5s. The British SAS was arguably the world’s premiere counterterrorist unit and overnight they had unwittingly become the world’s best submachine gun salesmen. MP-5s were everywhere.

Here in the U.S. we still are sort of free. Our government does not trust us with quite the same toys they get to have but that adventurous individualism that built the country in the first place conspires to arm American shooters with some fairly close facsimiles within the confines of our convoluted firearms laws. As such, using street-legal semi-auto HK-94s and assorted clones as a starting point, American gun magicians went to work polishing on these rough stones.

Original Patterns

The Germans arguably set the standard when it comes to weapons design in general. They thought up everything about the MP-5 in the first place and factory-built variants were legion. Integral as well as detachable suppressors graced the muzzles and butt stocks came in three variations while a stubby butt cap with a sling swivel was an option as well. The basic chassis came in two factory variations. The standard length was 21 inches long with the stock retracted while the stubbier K version ran only 12.75 inches without a stock at all. As a result of this length disparity and subsequently reduced bolt travel the rate of fire for the long version hovers around 750 rpm while the K model zips along at nearer 1,000.

Shooting 9mm subguns is positively serene. Recoil and muzzle blast are trivial and ammo is cheap. What serves as a pleasant time on the range, however, equates out to controllability and tactical effectiveness in darker places. In my experience, faster running guns are harder to control and subsequently less precise in practical use. I am coming to suspect that enterprising American gun tinkerers might have found the sweet spot in MP-5 submachine gun design.

Enter the Hybrid

In genetics, a hybrid is a selectively bred offspring designed to incorporate desirable characteristics from its biological progenitors. Hybrid crops are more productive and less susceptible to pests. Hybrid cars are more fuel efficient and thusly environmentally friendly. In this case a hybrid MP-5 combines the best features of the MP-5 family into a single optimized chassis.

The HK MP-5K PDW (Personal Defense Weapon) is brilliantly executed. Incorporating what was arguably the world’s first vertical broomstick foregrip and a stubby barrel configured for a muzzle-mounted suppressor, the MP-5K PDW is delightfully compact and maneuverable. The only real down side is that the K model receiver just shoots a little bit too fast. For the same reasons that most committed American machine gun enthusiasts own at least one MAC submachine gun yet seldom take it out to the range after advancing a collection past that point, the MP-5K PDW just shoots a little bit too fast to be ideally controllable.

By contrast, the full-length MP-5 enjoys a near-perfect rate of fire for a 9mm subgun but, while admittedly short and light, is not quite optimally thus. It is as a result of this tactical quandary that the “Reverse Stretch” MP-5 makes its entrance.

Guns in Cyberspace

The internet has revolutionized most everything in modern culture. Adherents of the most obscure hobbies, proclivities, and religions who might otherwise have thought of themselves as utterly alone in the universe may now appreciate that the planet is seemingly awash in those similarly inclined. There are websites attuned to people of any imaginable passion, and the net has brought together gun enthusiasts of all flavors and fractionated them into their individual species. As a result, HK enthusiasts on this side of the pond can gather electronically at will to compare thoughts and critique projects. The end result is better products through shared knowledge. It is also an entirely new lexicon.

To my knowledge the H&K company never offered the hybrid MP-5 we call the “Reverse Stretch” as a commercial product. That is a shame. The thing runs like a champ.

Raw Material

The gun profiled in this article began life as a Vector Arms 89K pistol spruced up and outfitted with a registered full auto trigger pack. The vertical foregrip is standard HK PDW kit. The side-folding stock is a Choate product designed to allow the PDW side folder to mount on full size MP-5 and HK-93 platforms. As may be seen from the accompanying photos, the rear portion of the receiver retains the full length dimensions of the original parent. While the bolt carrier is a bit shorter and therefore a bit lighter than its full-sized counterpart, the resulting hybrid zips along at about the same rate as the big gun while retaining the basic diminutive dimensions of the smaller PDW variant.

On the range this means doubles and triples are child’s play from a platform already known to run as smoothly as a sewing machine. The overall package is small enough to be concealable under a modest jacket with the buttcap installed yet remains capable of the near-surgical precision for which the original MP-5 is so justifiably renowned. As a guy who has tasted an awful lot of handheld automatic weapons and written about them commercially for more than two decades, I think I’m in love.

The days of 9mm subguns as proper tactical tools have passed. Like dinosaurs of a previous era, more efficient predators now occupy the pre-eminent position on the food chain. As a result, these elderly guns now languish among those fortunate American tinkers who retain access to them some 30 years after the infamous law changed or in the arms rooms of tactical teams insufficiently funded for an upgrade. For raw, unfiltered recreational blasting, however, I think the Reverse Stretch MP-5K PDW` is the cat’s pajamas.

This article first appeared in Small Arms Review SAW (April 2013)
and was posted online on February 8, 2013


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