The new HK UMP45: Polymer Perfection in a Sub Gun?

By Stephen Gearing

Many users of submachine guns have said if the MP5 was available in a decent caliber, meaning .45 ACP, it would be perfect. Others comment that the MP5 is incomplete without a bolt hold-open device. Procurement types would like the purchase price of the MP5 and accessories to be cheaper by 30% or more. HK’s competition would not. Users of .45 ACP pistols have settled for the MP5 in calibers 9mm, 10mm or .40 S&W, but would have preferred one in the same caliber as their .45 handguns. Armorers would be thrilled not to have to explain to their users about the real purpose of the locking roller holder in the MP5 and why their occasional breakage and replacement is no big deal. Often the less-than-perfect ergonomic features (length and shape of the safety/selector lever, buttstock length, etc.) of the MP5 are overlooked by its superior surgical accuracy, reliability and controllability in all available modes of fire. Most will agree that the Heckler & Koch MP5 is currently the worlds’ most capable submachine gun and therefore most widely favored by those organizations that can buy and field the best submachine gun the world has to offer.

History will show that HK is not a company that rests on its haunches basking in the glory of its current product. HK has pushed the envelope of small arms design and performance many times in its 50 years of existence. HK has pioneered evolutionary if not revolutionary developments like the first production polymer framed pistol the VP70 in the early 1960’s. The worlds first caseless ammunition rifle the G11, a rifle that when tested in the U.S. elicited the statement from the US Government that the G11 and its unique self-consuming 4.92 mm rounds proved the feasibility of using caseless ammunition in a military field environment. The HK Close Assault Weapon System (CAWS), the worlds deadliest shotgun and the latest development from HK, the OICW, the futuristic replacement to the U.S. M203 in 2005, are “bullet launchers” pushed to the limits of technology and materials.

While many informed small arms enthusiasts have heard of these HK weapons there was an entire family of HK submachine guns developed almost twenty years after the first MP5 was assembled as a prototype in 1965. These prototype sub guns eventually brought along the genesis of HK’s latest submachine gun, the new UMP45.

In the early 1980’s the U.S. Joint Service Small Arms Program (JSSAP) office solicited industry for an Advanced 9mm Submachine Gun to arm both conventional and special operations personnel. Calling for advanced features and design the “JSSAP Gun” never advanced beyond prototype development, with the exception of 60 that were reportedly hand-made expressly for and issued to one American unit that will herein remain nameless. HK developed numerous models and submitted them for exhaustive testing. In the end the users decided to procure the off-the-shelf MP5 for their purposes and the new HK’s were relegated to their place in only the more exclusive history books. The HK54A1 with its 50-round drum magazine and the subsequent SMG and SMG II prototypes were advanced 9mm smg’s built by HK during the 1980’s for this military R&D program. The military’s decision not to purchase the new HK SMG did not deter HK’s drive to improve on the near perfection of the MP5. Throughout the late 80’s and early 1990’s HK continued work on the concept of modular submachine gun from which various configurations could be assembled by the operator for the specific mission at hand. The use of advanced polymer materials found their way not only into the magazine for the gun but also into the receiver and many non-stress-bearing parts of the weapon. Prototypes of the MP2000 and the MP5-PIP (Product ImProved) were constructed and tested and have lead to the series production weapon HK now calls the Universal Machine Pistol (UMP).

Available by mid-1999 the UMP45, chambered for the ever-popular .45 ACP round, is truly a compilation of HK’s decades of worldwide experience with the MP5 and the prototype weapons described above. Not able to properly “stuff” the short stubby .45 ACP round into the 9mm MP5’s envelope, a new dedicated model was called for and design work began on the UMP45 in 1996.

A quick inspection of the new UMP45 shows that once again HK has done its homework well. This “polymer MP5” has all of the capabilities and features of the MP5 and more and none of its drawbacks. It is obvious to this writer that a great deal of actual user input has been incorporated into the weapons’ design.

To say that the design and construction of the UMP45 is a departure for HK would be accurate. The years of HK stamping, folding and welding sheet metal to produce new weapon designs seems to have ended. The use of only the unique roller-locked bolt system also seems to be a thing of the past if you look at HK’s newest offerings in long guns. The excellent HK G36 rifle and the new UMP45 both employ polymers throughout to include the receiver and many internal parts. Metal inserts provide the strength and durability needed in the pressure bearing components of these weapons and provide the guiding surfaces for the bolt. HK claims the UMP45 has a minimum service life of 100,000 rounds.

The UMP45 employs the simple blowback operating principle with a relatively lightweight bolt with few moving parts (extractor, firing pin, and firing pin block). Of course the UMP fires from the closed-bolt position and a fixed barrel, removable for the unit armorer, is also standard equipment. A bolt hold-open device, or bolt catch as it is often termed, is standard on the UMP45 and can be easily disabled for those with that preference. Fully ambidextrous operating controls, to include easily reachable safety/selector levers, await the UMP45 shooter. Sounds good you say? Well it gets better. All of these features are definite improvements over the features of the MP5, as is the suggested law enforcement price of under $900. Yes that’s right, $900 U.S. dollars for an HK smg, hundreds less than an equally equipped MP5.

Obviously in following with HK’s attention to firearms protocol, the U in UMP has a meaning. The word “Universal” denotes the ability of the UMP to be converted in caliber though at this time only a .45 ACP caliber UMP is planned. The barrel and feed ramp, removable by the operator or unit armorer without special tools, can be exchanged along with the bolt to change the caliber. Offering the UMP first in caliber .45 ACP gives HK a fourth caliber in a sub gun, one that will be welcomed by those law enforcement and military users carrying .45 caliber handguns. The UMP45 will easily handle a steady diet of ball, hollow-point and +P ammunition and even limited amounts of the cosmically all-powerful .45 Super round. Few other makers of smg’s offer more than just the basic plain Jane 9mm sub gun. No one offers a .45 ACP submachine gun that even comes close to the UMP45, especially considering the unit price and the performance of this newest HK tactical weapon.

The HK designers changed what needed changing on the MP5 to create the UMP and left the good things be. They correctly and intentionally left the operating controls of the UMP in the same position as those of other HK weapons. In this way a user already trained with and possessing well established muscle memory for the controls of their trusty MP5, G3, HK53, or even the new G36, will find the controls of the UMP45 right where they should be. Though like the HK G36 rifle, internally the UMP operates differently from its roller-locked cousin but its operating controls and sights are the same and therefore similar and comfortable to the seasoned user. New users will find the operating controls of the UMP to be friendly, well placed and easy to actuate.

Like all HK’s the operating controls of the UMP45 allow the strong (firing) hand to remain in place on the pistol grip while the free weak (non-firing) hand actuates the operating controls. The cocking lever, magazine release lever and bolt catch are easily actuated by the shooter with the weapon still in the shoulder firing position and thus ready for immediate use. The safety/selector levers of the UMP45 are of course ambidextrous but have been redesigned to insure that even “Stubby” with his abbreviated digits can still rotate the safety/selector lever into the firing modes without the need to rotate the grip of the strong hand.

The bolt catch resembles and functions like that of the M16 or M4 and is actuated by the follower of the empty magazine. A quick jab of the thumb during magazine insertion closes the bolt and “primes” the chamber with a live round. Simple and efficient, no wasted movement. Clever those Germans!

The UMP45 is delivered with fixed iron sights and molded-in attachment points for mounting rails (MIL-STD-1913 “Picatinny” rails) or other accessory devices. The rear sight is of a flip-up design with both open “V” shaped and peep apertures selected by HK to allow for both low-light/fast target engagements and for accurate firing at smaller or long-range targets. A metric Allen wrench is provided with the weapon for both windage and elevation adjustment, both made in the rear sight assembly. The front sight is a hooded post similar in design as that found on most all HK long guns. Optional tritium sights will also be available for the UMP by the time it is fielded in mid-1999.

The rail mounting points are molded into the polymer receiver of the UMP45 at four separate points. The rails can be attached with the same Allen wrench used for sight adjustment as desired by the operator. One six-inch section can be located on the top of the receiver in front of the rear sight. A second shorter four-inch section can be mounted at the left, bottom or right sides of the integral forearm of the weapon. Any device that can be attached to these rails like those produced for use on the M16A3 and M4A1 variants, to include light and sight mounts, vertical foregrips, QD sling attachments, etc., can be also used on the UMP45. Reportedly a rail will be available to allow the attachment of the HK MKII Universal Tactical Light (UTL), developed for the USP pistol, to the UMP. The weapon comes delivered with a protective guard or “hand stop” that mounts just below the front sight to insure that any wandering fingers of the operator do not find their way in front of the muzzle of the weapon.

The barrel of the UMP, as well as being removable by the user unit, also incorporates a unique quick detachable mounting system for attachment of muzzle mounted accessories such as sound suppressors and flash hiders. Bothersome threads are no longer necessary with this new system. This writer has never seen such a mounting interface as this and it is hard to believe one could be any faster, simpler or maintenance free. A simple depression of a knurled locking lever allows the sound suppressor to be mounted on the weapon in the time it takes to say “wow”! Removal is just as quick and easy. When mounted, the suppressor if free to rotate on the barrel but during our testing this did not change the point of impact. No collars, springs or locking sleeves are required nor do you need to push, rotate or pull the suppressor during mounting or removal from the weapon. Proven during extensive testing, the repeatability and accuracy of the weapon when suppressed is assured by this innovative attachment method. This is going to be without question the hot ticket for suppressor QD attachment.

Light weight, baffle-style aluminum Bruegger & Thomet (B&T) sound suppressors are being imported from Switzerland for sale with the UMP45. The accuracy of the UMP and point of impact were affected when the sound suppressor was mounted; they were improved! Reduction with ball ammunition is reported to be @ 20 dBA. No visible muzzle flash was apparent during our limited testing.

As with most all HK’s the 7.9 inch barrel is cold hammer forged. The UMP bore is chrome lined for durability, has HK’s trade-mark polygonal rifling profile and is forged with a rate of twist of 1 turn in 12 inches. Six “twist lines” with a constant right hand twist tend to the duties of stabilizing the projectiles during “the launch” sequence.

Like HK’s G36 weapon system the UMP45 is fitted with a robust folding stock that pivots to the right side of the receiver after depression of the locking button. It is held in the folded position by a molded locking feature on the receiver, which doubles as a brass deflector. The designers at HK, in an obvious attempt to improve the ergonomics of the weapon, have thoughtfully added a rubber buttplate and cheekrest to the buttstock. The layout of the UMP folding buttstock and its diminutive weight of 4 1/2 pounds unloaded would fit nicely in HK’s concealed shoulder carrying/deployment rig developed for the MP5K-PDW.

The UMP disassembles into two halves held together by a, for the lack of a better term, hinge and one single locking pin which stores in the buttstock during field stripping. The upper receiver contains the barrel, sights, cocking lever and sturdy folding buttstock. The lower receiver includes the flared magazine well, magazine catch, bolt catch, trigger mechanism, safety/selector lever and pistol grip. The bolt allows for the removal of the firing pin and spring and recoil spring assembly, of course without tools. The one-piece bolt includes a hollow cavity containing the little known but trademark anti-rebound tungsten granulate material employed by HK to insure positive locking of the bolt during firing, also used in the MP5. A clever firing pin block, actuated by the strike of the hammer, insures that the firing pin remains locked unless the trigger is pulled thus preventing slam fires or drop induced discharges.

Being a simple blowback operated weapon there is no need for the chamber fluting of the MP5 so brass exits the UMP looking unmolested. The ejection pattern is a consistent down and forward direction from the right side of the polymer receiver. The simplicity of the design made clean up after firing simple. No special tools or brushes are required and access to all of the critical areas for cleaning are enhanced by the upper/lower receiver design of the UMP. The polymer is resistant to any cleaning solvents that are safe to put your hands into and HK states little or even no lubrication is required.

The UMP has passed all of the normal grueling military-style testing during its development that HK has become famous for. Nearly every available type of U.S. and foreign military and commercial ammunition has been fired through the UMP during its two or more years of development, and in quantities that would make your reloading machine wince. During our firing session more than 1,000 rounds were fired without a single stoppage. No surprise for an HK weapon and this included ball, hollow-point, flat point, subsonic and even +P ammunition mixed randomly in the magazine.

The first thing that one notices when handling the new UMP45 is that it weighs almost nothing at all. Many comment that they could carry this one forever. At 4.6 pounds you probably could. The operating controls as designed are familiar and thoughtfully laid out like those of the MP5. The flared magazine well helps immensely when making fast magazine changes. The polymer 25-round magazine even has a clear plastic strip along its side for viewing and counting the remaining rounds inside. A shorter magazine of ten round capacity is also planned.

Filling the magazine was easy by hand. Magazine loaders are also available for extended range firing sessions and should make mag loading a breeze. “Lessons Learned” in the M3 Grease Gun magazine do not seem to have escaped HK during the design of the UMP45 magazine. A single feed position reminiscent of that used in the M3 is apparent. Sling attachment points are provided for both left and right handed shooters. The sling provided with the UMP45 is HK’s typical multi-purpose example of perfection, which is now assembled with black nylon webbing and manual release buckle.

Shooting any new weapon is always the final word in any evaluation. Many guns feel great in the hand and look good on paper but perform poorly where it really counts. The UMP45 did not disappoint us on the range to say the least. It was impossible to find any fault in the weapon at all. So we could have one complaint to log - we agreed that the UMP is not pleasing to look at but form always follows function and this gun works and handles wonderfully. The lightness of the weapon makes fast aiming and target acquisition mandatory during the classic CQB use of a submachine gun. The UMP45 is quick when acquiring multiple or moving targets and while firing on the move. Shooters of a smaller stature will appreciate the quick handling merits of the UMP45 for sure.

The recoil impulse to the shooters shoulder was notably more than that of the MP5 in 9mm. One would not expect a .45 ACP SMG launching 230-grain slugs down range to recoil like a 9mm throwing its 124 grain ball rounds into the wind. Providing far more muzzle energy than a 9mm submachine gun, the UMP45 provides far superior terminal effects when compared to weapons in other calibers, except maybe the 10mm MP5 with hot ammunition. This is especially the case when firing subsonic ammunition in a sound suppressed mode, a scenario where 9mm sub guns have often faired poorly.

For comparison purposes we were able to bring together MP5’s in all three available calibers to test along side the .45 caliber Universal Machine Pistol. We tested the four weapons side by side for accuracy, controllability in burst and fully automatic modes of fire, to include the tell all 25-round “Hell Mary” burst. While often argued as being unrealistic for a tactical weapon, the shooters ability to control fully automatic bursts beyond two or three rounds from a standing unsupported position allows direct comparison of the weapons potential controllability for worse case scenario firing.

Semi-automatic accuracy of the UMP45 was excellent, comparable with that of the MP5 in all calibers. Firing at 100 yards the UMP45 placed all rounds within a six-inch group on par with the 9mm, .40 S&W and 10mm MP5’s. The hold at 50 yards was dead on and knothole size groups at 15 and 25 yards in semi-automatic mode were easy, both with and without the sound suppressor mounted. Our Hell Mary burst test showed that when using the proper fundamentals of stance and weapon control it was possible to get 20 or more hits on an E-style kneeling silhouette at 25 yards distance with the UMP45.

For speed we employed the talents of a very experienced competitive shooter from our nations leading law enforcement tactical team. Well versed with a decade of experience shooting the MP5, this genuine “operator” showed that accuracy is only good if it can be maintained “at speed”. In the world of close quarter’s battle, hits and speed win gunfights. Our drill involved shooting two two-round bursts on a single 1/3rd size steel silhouette from 15 yards. Firing from an unsupported shoulder position the PACT timer recorded the results. Time and again this shooter completed this drill in less than 1 second from the ready position, both with his issue MP5 and the UMP45 firing 230-grain ball ammunition. Admittedly unfamiliar with the new UMP45, within minutes with little practice his first rounds were fired and on target in @ .70 seconds! We were impressed as was he.

Simple blowback, no locking rollers, light weight. None of this seemed to matter with the UMP45. Hits in the 2-round burst mode were within 2-4 inches of the point of aim at 15 yards, more than sufficient to insure the intended effect on target and to prevent misses that might endanger innocent bystanders. All this and with 230 grain .45 caliber slugs to insure the job is done right the first time. This is great news for the tactical teams around the U.S. and especially those looking for improved terminal performance from their submachine gun in the sound suppressed mode. This gun would also make an outstanding squad car carbine with the semi-automatic only or semi-automatic and 2-round burst trigger mechanism.

HK has done it again! They have created the first and only true modern production .45 caliber submachine gun that competes head to head with the abilities of the famous 9mm MP5. While doing this they made sure that it was better, lighter, less expensive, more user friendly and far less complicated than the treasured MP5. Best of all the UMP45 is available at a price where an agency could nearly buy two UMP’s for the price of one comparably equipped MP5/10 or MP5/40. Thanks HK!

This article first appeared in Small Arms Review v2N5 (February 1999)
and was posted online on August 26, 2016


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