Heckler & Koch's New USP LEM DA-ONLY Trigger System

By Jim Schatz

Heckler & Koch recently announced to the world the official existence of a radically new DA Only trigger system designed for the USP Pistol family. To many experts the success of the otherwise excellent USP pistol has been hampered by its relatively poor, heavy yet very reliable conventional DA trigger pull. This new system has been designed to replace the conventional USP DA Only system in an attempt to compete head to head with Single Action and Safe Action pistol designs by offering its Law Enforcement users with a vastly improved DA Only trigger pull. This new system has been available for more than one year having been developed in its final form for at that time an unspecified large U.S. federal law enforcement agency.

The “LEM”

This new trigger/firing system is termed the Law Enforcement Modification or LEM for short. The system is comprised of a set of six unique drop-in parts that can be installed in existing USP pistols, both full size and compact models. These parts include the trigger bar, sear, catch, hammer, cocking piece and cocking piece spring. As the name implies the LEM trigger system is currently being offered to military and law enforcement agencies only and replaces the standard USP variant 7 DA Only system beginning in 2001. At this time due to demand HK is only offering this system in new USP’s and not for retrofit into existing fielded pistols. It is yet to be decided if the LEM system will be offered on the commercial market.

How it Works

The LEM is Double Action Only mode of operation wherein the hammer is fully cocked and released with each full depression of the trigger. However, that is where the similarities end. Unlike conventional DA Only trigger systems, the HK Law Enforcement Modification uses the rearward movement of the slide to fully cock an internal and separate “cocking piece” positioned within a slot within the hammer itself. The hammer returns forward with the slide after loading or firing. The internal cocking piece however, located within the hammer, is retained in the cocked position by the sear. When the trigger is pulled the hammer is moved fully rearward through slack to a point where it contacts the sear. It is at this point that the shooter first feels appreciable resistance to the trigger.

As the sear is disengaged by the application of pressure on the trigger the cocking piece rotates on the hammer axle and drives the hammer forward to strike the firing pin and thus fire the chambered round. The amount of force required to release the hammer can be set at 4.5 - 5.0 pounds or 7.5 - 8.0 pounds at the preference of the user with a simple change of the firing pin block spring. A normal USP firing pin block spring provides the 5 pound trigger pull. A newly designed spring of greater strength when installed will increase the trigger pull to the 8 pound range. This spring is easily exchanged using only a punch and small hammer.

“Power Assisted” Trigger Pull

The obvious advantage of the HK LEM system is the reduction in trigger pull weight over conventional DA Only systems (generally 8 to 13 pounds or more). However, to the shooter that is only the beginning of the many advantages of the LEM over competing trigger systems. The LEM eliminates the need for the shooter to struggle against the resistance of the hammer spring and geometry of the internal parts to cock the hammer during the rearward depression of the trigger while at the same time trying to keep the sights in alignment to hit the target. This can be difficult for many experienced shooters and down right impossible for new shooters or shooters with small or weak hands. In the HK LEM the action of cocking the DA Only hammer is completed by the rearward movement of the slide, not by the shooter pulling the trigger. Therefore the shooter only feels the light slack and then short resistance before the hammer is released to fire the chambered round. In the LEM, a bit of the energy produced by pulling the trigger and firing the chambered round is recycled by the pistol to cock or “pre-load” the two-part hammer arrangement. Power Assisted DA Only firing. Hiram Maxim would have been proud!

The LEM trigger pull has been described by some experts as a Single Action in its feel but with the long slack and thus the built-in safety margin of a DA trigger system. Smooth, crisp, with little or no stacking or staging and yet safe and simple to use, especially for those shooters with small hands or limited hand strength.

An extremely short trigger reset distance of @ .241 inches comparable to that of many excellent Single Action (SA) designs (the trigger of an general issue M1911A1 resets at .120 inches for comparison), allows for fast follow up shots not normally available in conventional DA, DA Only and most Safe Action designs. The LEM system offers the shooter the same trigger pull for each round fired and thus eliminates the difficult transition from DA to SA that is experienced with conventional DA/SA pistols.

Unlike many conventional DA Only and Safe and Single Action designs the LEM allows the shooter the ability to restrike the same stubborn primer with a second squeeze of the trigger. No manual manipulation of the hammer or slide is required to do this.

Heavier Springs, Lighter Trigger Pull?

Because the recoiling slide is used to cock the internal hammer, a stronger hammer spring can be used without increasing the weight of the trigger pull. This stronger hammer spring improves the function of the handgun by slowing down the rearward movement of the slide and thus improving feeding from the magazine, especially when firing today’s more powerful ammunition. This action improves the service life of the hammer and recoil springs and other component parts of the handgun while at the same time enhancing long-term reliability.

The LEM provides the law enforcement or military user with the simplicity and same trigger pull for every round fired, the inherent safety of the long DA trigger pull employed successfully in DA revolvers for more than a century and the absence of external controls, to include safety or decocking levers. With the USP’s ambidextrous magazine release the LEM equipped USP is totally ambidextrous. At the same time the quality of the LEM trigger pull is superior to conventional DA Only systems and many SA and Safe Action designs. These attributes help promote improved accuracy and probability of hit for the user, especially while firing under stress. Shooter and bystander safety is enhanced, as there are no actions required by the user after firing such as decocking or engaging a manual safety as no such controls are required.

For users that require a manual safety that blocks the release of the hammer, the modular nature of the USP design allows one to be added to the LEM system as well. This includes a left, right or ambidextrous frame-mounted safety lever, which blocks the release of the sear. This option could provide a greater margin of safety should the operator accidentally squeeze the trigger during improper handling, during the typical “gun grab” where an assailant attempts to take and shoot the officer with his or her service pistol or to help prevent accidental shootings at the hands of unauthorized persons, such as children “home alone”.

An innovative solution from the creator

The idea of the LEM design was born in 1997 by Helmut Weldle, the USP designer at HK GmbH in Germany to address the need for a vastly improved DA Only trigger pull to compete with Safe Action designs. Since its official release in 1999, the U.S. Immigration Service has since adopted this new system for the USP40 Compact Pistol, which is being issued to plain-clothed INS Inspectors and Deportation Officers. More recently the German Police have also adopted a slightly modified version of the LEM system in a new HK 9mm pistol called the P2000.

During development testing multiple USP40 Compact-LEM pistol samples fired an amazing total of 15,575 rounds per pistol without a single malfunction, stoppage or broken part. 25-meter accuracy firing of the USP40 Compact-LEM with its 3.58-inch barrel from the hand supported by sandbags only, firing duty ammunition provided a 5-shot group average of 2.41 inches for 18 targets fired. The LEM system has also successfully passed the standard NATO drop test requirement of 2 meters on a concrete/steel surface on all six attitudes.

Parallel Developments

Though they accomplish the same goal of an improved DA Only trigger pull, the HK LEM and new Para-Ordnance “LDA” (Light Double Action) systems differ considerably yet were clearly parallel designs from two separate firms over nearly identical periods in history. Unlike the Para-Ordnance system however, the patented HK LEM does allow for multiple strike capability by simply resqueezing the trigger. The HK LEM is available in a wide variety of models to include full-size and compact versions in calibers 9mm Luger, .40 S&W, 357 SIG and .45 ACP.

The Future

Whether the new Heckler & Koch Law Enforcement Modification will appeal to the general U.S. law enforcement community is yet to be determined. The general release of test samples for evaluation beginning in 2001 should answer this question. From the response to date from the INS/Border Patrol, the German Police and those who have handled or fired the USP with LEM parts on board, this new offering may once and for all end the discussion about when HK will offer “a really good DA trigger pull” in the USP. Well it is here already and it is the LEM.

This article first appeared in Small Arms Review V4N8 (May 2001)
and was posted online on June 6, 2014


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