Heckler & Koch (pronounced like "Coke") has recently developed a new fire control system for their line of USP semiauto pistols. It is called the LEM (Law Enforcement Modification) trigger. It was developed in response to the desire of some law enforcement agencies to have a DAO pistol that did not have the disadvantage of a relatively hard trigger pull. New LEM-equipped pistols are being produced for the LEO and civilian markets, but you're not likely to find any of them yet (as of late 2003) on the shelves of your favorite gun shop.
However, being modular in design, any USP pistol can be converted to the LEM system. Once converted, the pistol can always be chanaged back to its original configuration, provided the original parts are retained. The set of parts needed to convert a USP pistol to LEM costs approximately $50. However, due to liability issues, H&K will not sell the parts directly. Rather, they require that you send them the pistol. They will make the conversion for $96 (parts and labor), test fire the weapon, and ship it back to you with a bag containing the original parts. I was told the conversion process would take 3 to 4 weeks, but I had my USP Compact .40 S&W back in less than 2 weeks.
USP pistols come in a number of different fire control configurations (called "Variants" by H&K). There are now over 16 such configurations, although most lists (even their web site) only show about 10. The list seems somewhat confusing at first, but after review it becomes rather intuitive. There are TDA (Traditional Double Action) variants that can be obtained with a control lever that acts as just a decocking lever, or that acts as both a decocking lever and a safety lever. These can be obtained in right hand or left hand versions. That makes 4 variants. Then there are DAO (Double Action Only) variants that can be obtained with or without a safety lever on the right or left side. That's 4 more variants. And so on.... My H&K USP Compact was originally a Variant 1, which meant it was a TDA pistol, with a dual-purpose control lever on the left side of the pistol. That is the most common variant sold by H&K.
All USP pistols come with a firing pin block that is disengaged when the trigger is pulled to the rear. Full-size versions of the USP have a spurred hammer, whereas Compact versions come with a bobbed hammer (for concealment purposes). In order to describe the new LEM trigger system, it will help to first review the TDA and DAO versions of the USP pistol.
The DAO version is the simplest configuration. When the slide is cycled, either manually or by firing the pistol, the hammer follows the slide forward to a position just off the firing pin, Nothing is cocked in the pistol. Each time the pistol is fired, it is with a long, relatively heavy DA (Double Action) trigger pull of 10 to 12 pounds. H&K's are not known for a beautiful factory DA trigger pull, but that can be achieved easily by a number of gunsmiths. The DAO version can be obtained without a control lever, or with a frame-mounted control lever that has two positions: Position 1 (up) is Safe, and Position 2 (horizontal) is Fire. If the pistol is dry-fired (or fired with a dud round), the hammer will move all the way forward, resting on the firing pin. Cycling the slide a little, pulling the trigger a little, or pulling back the hammer a little will move the hammer back to it normal just-off-the-firing-pin position.
The TDA version is the most common configuration. The control lever has three positions: Position 1 (up) is Safe, Position 2 (horizontal) is Fire, and Position 3 (down) is Decock. The lever is spring-loaded out of Position 3. When the slide is cycled, either manually or by firing the pistol, the hammer is cocked and remains rearward. At this point, the pistol can be fired in SA (Single Action) mode with a short, light 5-lb trigger.pull. If not immediately fired, the operating lever can be moved up into the Safe position for cocked-and-locked carry, or the operating lever can be moved down momentarily to the Decock position. This will decock the pistol, safely dropping the hammer to a position just off of the firing pin. The weapon is now in DA mode, and the pistol can be fired with a long, heavy trigger pull of 10 to 12 pounds. I should note that the operating lever can be placed in the Safe mode regardless of whether the hammer is cocked or not. Also, moving the control lever to the Safe position does not lock the slide. This gives the user the option of loading or unloading the pistol while it is in the Safe condition. Like the DAO version,if the pistol is dry-fired (or fired with a dud round), the hammer will move all the way forward, resting on the firing pin. Cycling the slide a little, pulling the trigger a little, or pulling back the hammer a little will move the hammer back to its normal ust-off-the-firing-pin position.
Heckler & Koch was aware that many CCW-holders and law enforcement departments are uncomfortable with cocked-and-locked carry. They also knew that many people did not like the transition from DA to SA mode in TDA pistols. Although DAO pistols eliminated the need for such a transition, as well as eliminating the need for an external safety lever, they were often more difficult to achieve the best accuracy due to the long, heavy trigger pull required for each shot. The H&K LEM trigger, like the Para Ordnance LDA trigger, was designed to overcome these problems.
The H&K LEM pistols, like their regular DAO models, can be obtained with or without a control lever safety. I chose to not have the lever retained when my pistol was converted to LEM. I did this for a number of reasons: (a) The safety isn't necessary; (b) No liability issues of whether the pistol was on safe or not prior to firing; (c) To eliminate concerns that the pistol might be accidentally put on Safe; (d) The pistol is more comfortable in an IWB holster without the control lever; and (e) The absence of the control lever gives a cleaner access to the slide lock release lever. Other owners may have different priorities and may opt for having the control lever present. The LEM pistols have a two-part hammer -- an internal hammer and an external hammer. When the slide is cycled, either manually or by firing the pistol, the internal hammer is cocked but the eternal hammer follows the slide forward to its normal just-off-the-firing-pin position. The trigger is in its forward position. To fire the weapon, the trigger is pulled rearward through a long, light trigger pull of something less than 2 pounds. Near the end of that trigger stroke, resistance is encountered. If additional force is then applied to the trigger, the pistol will fire, cycle, and start all over again.
The LEM fire control module can be obtained in either of two trigger pulls. The "light trigger" is 4.5 to 5.5 pounds. The "heavy trigger" is 7.5 to 8.5 pounds. I chose the light trigger for my USP conversion. When I received the pistol back from Sterling, VA, the trigger measured just under 5.5 pounds on my RCBS trigger pull gauge. I anticipate that it will lighten up a little with use.
H&K advertises that their LEM trigger has a "very short trigger reset." I found this interesting, because the very long trigger reset is one of the main disadvantages (for me) of my Para Ordnance LDA pistol. I also wondered how they could have a short trigger reset, when the trigger had to move forward into its DAO position after firing. Well, here is one of the main advantages of the H&K LEM trigger over the P-O LDA trigger. After firing an LEM-equipped H&K USP pistol, the slide cycles faster than the shooter can release the trigger. This occurs in all semiauto pistols. If one fires the LEM pistol, and keeps the trigger back after firing, the hammer remains back! At this point, the shooter can let the trigger go forward just a short distance; the trigger will reset, the hammer will stay to the rear, and the pistol will be ready to fire again. If this is done repeatedly, firing the pistol will be just like firing a pistol in SA mode. There will be short trigger pulls of about 5 lbs, short resets, and hammer staying cocked after each shot. However, if the shooter lets the trigger go all the way forward after firing it, the hammer will go forward to its normal just-off-the-firing-pin position. At this point, the pistol will be in the same condition that it was after initially loading, and it may be safely holstered. Although the internal hammer remains cocked, letting the trigger go forward is almost like "decocking" the external hammer, but without having to manipulate a decocking lever.
There is another difference beween the H&K LEM trigger and the P-O LDA trigger. Like the other USP versions, if the LEM version is dry-fired, the hammer will go all the way forward and will be resting against the firing pin. At this point, unlike the P-O LDA, the trigger on the LEM can be pulled (against a very strong hammer spring) and a second strike on the primer can be obtained, if one wishes. This is not an advertised feature, but it exists nonetheless. I don't find it very useful--the chances of a factory primer not being fully seated are rather remote, and I believe that performing a "Tap-Rack-Bang" procedure is the best recovery. Besides, the hammer spring on the LEM version is stronger than on H&K's other pistols (for primer strike reliability), and the trigger pull required to achieve a second strike is substantial. I was unable to measure it, but I'd estimate that it is in the 16 to 20 pound range.
So, there you have it. The functioning of the LEM version of the Heckler & Koch USP pistol is similar to that of the Para Ordnance LDA models. However, unlike the LDA pistols, the H&K LEM trigger has a short reset. I should note that the term "very short reset" used by H&K is somewhat of a misnomer. It is definitely very much shorter than my P-O LDA pistol, and it is even shorter than my Rugers or the original USP TDA reset. But it is not as short as my Kimber 1911 pistols. It is about the same as the reset distance on my Glocks.
A word of caution... I have mentioned dry-firing here several times. The reader should be advised that, due to the design of the USP firing pin and firing pin block, significant stress is placed on the firing pin during dry firing. Because repeated applications of this stress can lead to firing pin breakage, Heckler & Koch recommends that snap caps be used when dry firing. I initially disregarded this advise, and my firing pin broke after a few weeks. H&K replaced it at no charge when I shipped the slide back to them, but it could have been avoided. And changing the firing pin on a USP is considerably tougher than on a 1911. Not only must the firing pin, firing pin spring, firing pin block, and firing pin block spring be held captive during the process, but the entire mechanism is held in with a roll pin, rather than a stop like the 1911.