Great write up again Jim! Always learn something new each time.
After receiving several questions recently from forum members relating to the UMP and reviewing a post I did about this time last year, I realized that original post was not as in depth as it should have been. I present the following update to that original report, following my attendance of the UMP Armorer course, below for your review.
I'll begin by saying that I never held any great disregard for the UMP, or felt that is was just a cheap and simple replacement for the MP5, as has been mentioned from time to time. I've got a fair amount of trigger time on the platform and have learned to adjust to the unique recoil during automatic fire. Honestly, I just let my preference for the MP5 series prevent me from understanding the unique and innovative design and safety features of the UMP. Most will be obvious to our forum members, while others are not, but here is a brief history and key design features for a greater appreciation of the UMP. Hopefully, this will teach you something you didn't know about the UMP as well.
To understand the UMP, you obviously have to understand the direction of the company at the time of its development, as well as the famous submachine gun that proceeded it.
For decades, the G3 and MP5, with their stamped steel construction and delayed roller locking bolt blowback system, had been the mainstay of HK’s production. The MP5 series specifically, by the late 1980s, had established itself as the premier submachine gun of the world, with use by military special operations units, federal agencies and local SWAT units. Yet as that decade came to a close, there began requests from some of the more premier end users of the MP5 for a larger, more capable caliber offering. One specific US Special Operations unit was finding that while excellent in close quarters battle, the MP5 left a bit to be desired when they stepped out into the streets outside their target house and had to engage more distant targets armed with AKs.
HK designers attempted to work within the confines of the MP5 to enlarge the caliber offerings, but to that specific unit’s dismay, the .45 caliber cartridge was just too large. To accommodate it, an almost completely new weapon would have needed to be created. Yet, for the FBI, who at the time was wanting to upgrade from 9mm to what ended up becoming, both 10mm and .40 S&W, HK was able to stretch the internal dimensions just enough to create what we know as the MP5-10 and MP5-40.
At the same time as this MP5 series expansion/product improvement development was underway, HK received a serious blow. Their incredibly expensive G11 program, which was being developed to replace the G3 in German military service, and hopefully lead to much greater contracts to follow, had left them overextended. With the fall of the Berlin Wall and the reunification of Germany, the German military was to begin a massive downsizing and the necessity of such a revolutionary weapon to defeat the Russian hordes attacking across the Fulda Gap was no longer the great threat it had been just a few days prior. In need of a significant capital infusion, HK was offered up for sale and British Aerospace bought the company, placing it under its land weapons division, Royal Ordnance.
With this new ownership came a massive downsizing within the company and restructuring to cut away what was seen as inefficient or distracting endeavors. Part of this focus on minimizing cost and maximizing profit came with a directive to transition from the expensive and time consuming stamped steel construction weapons to more rapidly and inexpensively produced polymer construction weapons.
The first long gun for HK’s new focus remained an answer to German’s need for a new military service rifle. That focus needed to be on a cost-effective “family of weapons”, based on the now NATO standard 5.56mm cartridge. The end result was the G36 series and its success lead to what was meant to both answer the call for a higher caliber offering to their submachine gun line, albeit arguably about a decade too late, and the intended replacement for the MP5 series. This offering was released in 1999 as the Universal Machine Pistol or UMP.
Sharing many construction and design features of the G36, but with an obvious layout for familiarization transition from those accustom to the MP5 series, the UMP represented a strange duality of old meets new. Ditching the delayed roller locking direct blowback system of the MP5, HK designers chose to simplify both cost and operation by incorporating a simple direct blowback system, somewhat similar to the successful Uzi design. Yet, all this was done with a modular approach and while incorporating new safety features to make the UMP far more safe and accurate than other comparable designs.
First and foremost in efficiency, HK designers wanted to create one weapon, or more specifically a base receiver, that could be easily configured to different caliber offerings. This way, one gun could satisfy all the needs of their customers for a submachine gun. Their focus was to provide a .45 caliber option for the US military, a .40 S&W option for US law enforcement and a 9mm option for their European and global market. To do this required that the receiver be made large enough and strong enough to withstand the .45 caliber cartridge. The smaller cartridges would just have more room.
Utilizing a polymer construction around sections of steel inserts, the receiver is both lightweight, durable and very simple to maintain, especially advantageous in maritime environments or areas that cause less than ideal maintenance regimens.
Seen here is one of my favorite training tools for the HK Armorer Courses, the cutaway training model.
To incorporate an ever-growing demand for optics and attachments, four mounting points were incorporated for accessory rails, allowing quick and easy mounting access.
The sights were borrowed from the G36 design and their front hooded-blade and rear adjustable peep and partridge sights were seen from the start to primarily serve as a back-up option to users who most certainly would be adding some sort of red dot or reflex sighting option. As such, the low position of the sights aids in using a scope while still maintaining a cheek weld and the front sight, if desired, can be completely removed by simply knocking out the clamping sleeve that retains it in place.
The charging handle, though initially discussed to be of the same ambidextrous design as that of the G36, was instead placed in a similar position as the MP5. An obvious nod to muscle memory operation and ease of transition from those customers familiar with the MP5, the cocking handle is spring loaded to ensure that it remains in the forward and locked position during firing and is reinforced with a steel insert to prevent snapping during aggressive use (the original cocking handles did not have this insert).
Fitted into the steel-inserted trunnion of the receiver is the barrel. Held in place with one horizontally mounted barrel pin, the barrel is free floating and extends only slightly beyond the front of the receiver. Discarding the earlier “3 lug” and threaded muzzle design seen on the MP5 series, HK designers chose a unique, flanged-barrel design. Somewhat bell-shaped, with a small notch-cut out on the bottom of the barrel, the intent was to provide a quick and easy access for mounting suppressors and muzzle attachments. For suppressors compatible with these barrels, it has been found to be a very secure design, eliminating the issue common with threaded barrel designs where the suppressor, especially during full automatic fire, will begin to creep forward on the threads.
Easily one of the most unique design features of the UMP is the ability, at the user level, to change the barrels. One literally only needs to drift out the barrel pin with a hammer and punch and the barrel can be pushed back into the receiver and removed through the rear. Replacement is only slightly more complicated, as you have to align the barrel mounted extractor correctly within its receiver rail and attach it to the barrel before realigning the barrel within the trunnion and drifting in a fresh barrel pin. Though many people will attempt to reuse the original barrel pin, with a focus on always providing 100% reliability, HK recommends that all pins which involve metal to metal contact be one time use items only.
Below the barrel and mountable on the receiver, is another carryover from the G36 design, a removable hand stop to prevent the user's hand from moving in front of the barrel during firing. Over the service history of the MP5 series, with its relatively short barrel, the need for such a device had been clearly recognized.
On the right side of the receiver, again borrowed from the G36 design, a stock catch was incorporated to lock the folding, G36-style, skeletonized stock into the closed position. This stock design allowed for the weapon to be fired with the stock closed and the ejecting rounds clearing through an opening in the stock. Though clearly not a concern during development, a common complaint now is the length of pull of the stock when in its open position, with many users wishing HK had designed the stock to be a couple inches shorter or in a telescoping variant, still the stock is very robust and stable. Probably the most common stock modification seen here in the US, Hogue offers a UMP stock adapter which allows M4-syle collapsible stocks to be mounted, while still retaining the folding stock capability.
Below is a photo showing a UMP45 with both the Hogue stock adapter and B&T suppressor attached.
Besides mounting points for a sling, the original stock also incorporates a push pin holder. This common practice on HK stock designs helps to minimize the risk of losing that critical component during maintenance, especially in the field or low light conditions. It is also this one single push pin that allows the entire weapon to disassemble, instead of other HK designs which incorporate three or four. HK fan, Larry Vickers, joked that HK designers must have lost sleep at night about only incorporating one single push pin on the UMP.
With the receiver, barrel and stock group covered, we move on to the bolt group. As mentioned previously, HK designers chose a simple, direct blowback system for the UMP, but with several updates to increase safety and accuracy. First and foremost, unlike the vast majority of direct blowback submachine guns that proceeded it, which fire from the open bolt, the UMP does not. The drawback of an open bolt system is twofold. First, there is an increased chance of slam fire and second, first-round accuracy is degraded due to the force and weight shift that occurs with the weapon when the bolt comes forward for the first shot.
Simple direct blowback system submachine guns are also known for their large and heavy bolts. Without a more complicated locking and unlocking system, it is that bolt mass alone that is responsible for the reliable cycling of the weapon. Often misquoted as a bolt carrier, like any the other HK designs, with the UMP, there is only one large bolt, affectionately nicknamed the BAB or Big Ass Bolt. Its weight alone represents a substantial amount of the overall weight of the weapon. As mentioned above, the UMP bolt allows the weapon to fire from the “closed bolt position”. It does so by incorporating a firing pin housed within the bolt and incorporating several unique safety features to prevent slam fire and out of battery fire.
Here is a side by side comparison of the 9mm and .45 caliber bolts (about a half pound weight difference)
The majority of the earlier simple direct blowback submachine guns, operating from the open bolt, did so simply by having a detent milled or welded to the face of their bolt, with which to strike the primer of a chambered cartridge as the bolt came forward for each shot. Effectively, what you were getting with these weapons was a slam fire with each pull of the trigger. On the UMP though, the firing pin assembly is a separate unit. Positioned within the bolt itself, the firing pin assembly is held in place, incapable of being forced forward by a firing pin block. This firing pin block is actually a spring loaded portion of the firing pin assembly itself. Two raised bushings of the firing pin assembly are slightly spaced from each other by the tension of a compression spring in the rear of the firing pin. In this relaxed position, the rear of the firing pin sits just slightly short of flush with the rear of the bolt. An ingenious feature, HK designers created a channel along the length of the left side of the bolt, providing access to this firing pin assembly and these two raised bushings of it. Positioned within a guide rail within the left side of the receiver and attached to the barrel, is the UMP’s extractor. That extractor incorporates a small protrusion which fits directly into the channel on the left side of the bolt and it is that protrusion on the extractor which makes contact with the first of the two bushings of the firing pin assembly. Seen below is the firing pin assembly with the two extended bushings and internal compression spring.
When the bolt goes into battery, the protrusion on the extractor makes contact with the first bushing of the firing pin assembly and forces it to the rear and in contact with the second bushing on the firing pin assembly. Under pressure of the internal compression spring which separates those two bushings of the firing pin assembly, the firing pin is forced to the rear and outside of the confines of the bolt itself. This safety feature, designed to prevent out of battery fire, thus requires the bolt to have to be in battery in order for the extractor protrusion to make contact with the firing pin assembly and present the firing pin to be struck.
A secondary out of battery protection was also incorporated, utilizing the automatic catch within the trigger group. This catch is engaged each time the bolt moves to the rear, forcing the hammer back, where it is then held by a notch on the hammer. The automatic catch is then released each time the bolt comes forward again, into full battery, by the firing pin retaining pin, which serves this dual purpose role. Designed to protrude long enough and thickly enough out of the left side of the bolt, to actuate the release of the automatic catch, it ensures that the bolt is in battery before the hammer can be released.
Notice here the location and size of the firing pin retaining pin, which doubles as the automatic catch release.
The last safety feature HK designers incorporated to prevent out of battery fire was deep within the bolt itself. Like with their other designs, Tungsten granules were inserted and serve a similar purpose as a dead blow hammer. The slight delay that results between the bolt moving into battery and the secondary slap of the tungsten granules hitting the area just behind the bolt face ensures that the bolt is fully seated prior to the next round being fired.
Now that we have discussed the design features incorporated to prevent out of battery fire, we turn to the firing pin safety or drop safety, which prevents slam fire. That feature is actually found in the opposite end of a very long extractor, which runs the full length of the bolt from the bolt face to the rear of the bolt, within a channel on the right side. Somewhat arrowhead-shaped at its rearward tip, in its relaxed position, it sits directly in front of the point where the firing pin rests inside the bolt. The firing pin safety must be swept aside by the falling hammer in order to allow the hammer access to the firing pin. And of course in order for the weapon to fire, the hammer must first be released by the sear and automatic catch, which must in turn be released by the trigger, which is released by the safety/selector axle, but only after the extractor protrusion, with the bolt in full battery, has presented the firing pin to be struck. In short, an overly complicated description of an incredibly safe operating system. Who would have thought a simple blowback system weapon would be some complicated?
Notice the design of the UMP extractor/firing pin (drop) safety, with the extractor on the left end and firing pin (drop) safety on the right.
Easily unnoticed on the UMP bolt is a small hole in the base, close to the bolt face (seen below). The bolt design incorporates a vent/drain hole (similar to the original debut on the USP slide), which prevents lacquered bullets from "gunking up" the firing pin assembly and channel.
Another feature that most people overlook is the half-moon-shaped cutout on the right side of the bolt. Clearly seen in the following photo, this feature is designed to serve as a forward assist. With the simple blowback system of this weapon, there is no need to overcome the force of a rotating bolt system to get the bolt into battery. As such, if necessary, the operator needs only to place his thumb or finger into this recessed area of the bolt and press forward.
We finish the design of the bolt group with the recoil system, which is made up of the recoil spring assembly and the back plate and buffer. A very robust, universal recoil rod assembly allows it to operate without modification or replacement with all three caliber options and slides smoothly into the top of the bolt, similar to the design of the MP5-10, MP5-40 and MP5F bolt carriers. This recoil rod assembly rests squarely against a back plate and buffer, which is attached to the rear of the trigger group instead of the stock itself, like earlier designs.
Rounding out the UMP design, we finish with the trigger group. Unlike earlier HK designs, which required part modification to the internal trigger packs for use with the different caliber variants of their delayed roller locking weapons, the UMP “universal” trigger groups work without any modification at all. To do this, HK designers once again, leaned heavily on their successful G36 series. The internal components of both the G36 and UMP trigger groups are almost exactly the same. The main difference between the two being the bolt catch design and the fact that the UMP incorporates the magazine well into the trigger group, while the G36 does not.
Starting at that point of the trigger group, the large and wide magazine well of the UMP was clearly designed to accommodate the .45 caliber cartridge. Universal in nature, this design required that the two smaller dimension calibers would require an equally wide and thick magazine. Thus, the reason why sitting a MP5 9mm 30 round magazine next to a UMP 9mm magazine, will reveal the bloated appearance of the ump magazine.
Interestingly, with relation to the magazines, HK designers, with the .45 caliber magazine, were able to correct the reliability issues normally found in the double stack, single feed orientation of cartridges.
Viewing strips in the magazines provide a clear and ready identification of ammunition supply. Metal inserts are also used to reinforce the feed lips from spreading or breaking under pressure or when dropped.
Moving back on the trigger group, on the left side, and to satisfy their US customer base, HK designers incorporated a bolt hold open device, similar to that on the M16/AR15 rifles. This bolt catch is spring loaded and is actuated by the pressure of the magazine follower, which under spring tension, when the last round is ejected, forces the bolt catch up, where it makes contact with the feed pawl on the base of the bolt, blocking its forward movement.
Within the trigger pack area of the trigger group, as mentioned previously, is an automatic catch and sear, which make contact with the hammer in two different points. The safety axle also incorporates different amounts of clearance space for the trigger tail, depending on which position the selector is set in. In the safe position, the trigger tail is blocked by the safety axle from any reward movement. In the semiautomatic position, the safety axle presents a cavity large enough to allow the trigger tail to move to the rear and high enough to clear the sear notch on the hammer, but not the automatic catch notch. In the full automatic setting, the safety axle allows enough movement for the slide to be engaged and the sear to clear both notches on the hammer.
The burst function, of which the UMP, like its G36 predecessor, only incorporates a two-round function, is unique in the same fashion as the previous design from HK from the MP5 series and other delayed roller locking system trigger groups. It incorporates a counting function to allow two shots only with each trigger pull and then reset with each release of the trigger. That way, if the operator “short stroked” the trigger and only fired one shot, the next trigger pull would release two shots as intended, instead of finishing of the second shot of the first trigger pull. This is different than the burst design of many other manufacturers, like Colt, which on their M16A2 and A4 rifle’s three-round burst setting, if you “short stroke” the trigger pull and just get one shot off, the next trigger pull will only give you the remaining two. It cannot reset until the full three rounds have been fired.
Just to the rear of the selectors and on the right side of the trigger group, HK designers incorporated yet another safety feature. The UMP trigger groups employ a takedown block (seen assembled and disassembled below), which prevents the trigger group from being levered off the receiver when the bolt is to the rear.
Lastly, to help prevent the retaining pins in the polymer housing of the trigger groups from drifting out of position over time and repeated removal, steel inserts are provided in the left side of the housing to capture those pins and keep them in place. As such, removal of those pins is always from left to right and replacement is the opposite.
With all these design advances and safety features, we’re left wondering if HK hit the mark with their plan to have the UMP replace the MP5 series. Clearly, history has proven that is not the case. Speaking with HK Defense military and federal law enforcement sales representatives will reveal that they still receive regular purchase requests for MP5 series weapons to this day; far more than the demand for the UMP. That is not to say that the UMP has not been successful. It clearly offers customers with a unique capability. The mass appeal of the MP5 may just be too great to overcome, even with another submachine gun offering from HK.
No surprise to the members here though, that in the US, the ability of the civilian version of the UMP, the USC, to be converted into a clone of the UMP has been a big draw for those who want a .45 caliber SBR on rifle counterpart to their HK pistol or long gun collection. I have personally owned a .45 caliber SBR conversion and currently have one built from one of the very rare and new factory demil 9mm UMP kits. Its light weight makes it very handy and maneuverable, but like its bigger caliber brother, the unique recoil impulse associated with the simple direct blowback operation takes some getting used to.
Still, the UMP has become one of my favorite HK designs, admired for its modularity, simple maintenance and well-designed safety features. As such, I find almost equal enjoyment working on the UMP as I do shooting it.
As a way of commemorating each HK Armorer Course Certification, I create another custom frame of that weapon for my gun room and here is mine for the UMP.
Great write up again Jim! Always learn something new each time.
HK Certified UMP and VP9 Armorer
Impressive as always James! Thank you sir!
Thanks for a great write up. I wish the UMP would catch on more than it has. It, like the P2000 just don't seem to get the credit they're due!
These types of posts really need to go in the World of HK Reference Library. Which is in and of itself due for an overhaul. I know it's a low priority project for the admins, but it would really help to spruce up the place a bit.
Sent from my iPhone using Tapatalk HK, probably while driving.
01 / 03
just wanted to express my appreciation for all the hard work you do in presenting each course you do. The amount of time it must take you to write all these up is greatly appreciated.
Hk has the Gray Room located in northern VA. Heading south out of the Mid-Atlantic region of the USA, you cross into the Southeast Region , and home to the Blue Room which is strategically located close by to Marines Corps Base Camp Lejeune , the Home of Expeditionary Forces in Readiness . The active Curator , resident Armorer , and ring leader is James , heretofore referred to as Marine0303 . Tours available on request (depending on chow time and homework activities ) .
And thanks, guys. As always, I enjoying sharing the HK knowledge with all of you. All the effort it takes to put posts like these together is worth it when you all appreciate it and actually learn something new about a HK weapon you may have thought you already knew pretty damn well.
In the process, I even learn a bit myself. In writing this, I learned that there is a max limit to how many characters you can put in a single post on this forum. This post was large enough to max that limit out.
This also represented my 4000th post. Pretty cool.
Wow. Did not know the max character limit. Even in replies, your posts are quite informative.
I noticed you were approaching 4000. Glad you saved it for something special, and not a "use the search feature" like I did for my 1000th, 1500th, and well, pretty much any in-between.
Sent from my iPhone using Tapatalk HK, probably while driving.
01 / 03
Thank you for taking your time to write a great article and congrats with the #4000!
Two related questions:
1. "Their focus was to provide a .45 caliber option for the US military, a .40 S&W option for US law enforcement and a 9mm option for their European and global market."
Why .40 and .45 for the US and 9mm for the rest of the world? Is the 9mm round only considered inadequate in the US?
2. To my knowledge the UMPs are available with the NAVY(full auto) or FBI(semi) trigger group. I've used FBI(semi auto) on my conversion because it is semi auto only. But why would the government agency such as FBI purchase the submachine guns without the full auto capability?