How to Install an LEM Trigger on an HK USP

The HK USP -- Universal Self-loading Pistol -- is a high-performance semi-automatic handgun chambered in 9 mm parabellum, .40 S&W and .45 ACP. The pistol's overall design was influenced by law-enforcement and military personnel for optimal field performance. The LEM (Law Enforcement Modification) trigger-conversion kit can be installed on the pistol to increase handling and trigger function. Installing the LEM trigger on the HK USP can be accomplished using a few gunsmith tools.

Things You'll Need

  • 1/16-inch Punch
  • 2.5 mm Punch
  • Hammer
  • Padded gun vise
  • Bench block
  • Needle-nose pliers
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Instructions

    • 1

      Remove the magazine. Pull the slide to the rear. Inspect the chamber to make sure that no live ammunition is present.

    • 2

      Rotate the slide-release lever downward. Push the slide forward and off the weapon frame. Remove the slide-release lever.

    • 3

      Hold the weapon frame upside down. Depress the lanyard-loop insert (lockout mechanism) on the rear of the handle. Drift out the lanyard-loop insert pin using a 1/16-inch pin punch. Remove the lanyard-loop insert and lockout mechanism.

    • 4

      Secure the frame in a padded gun vise. Make sure that the top of the frame is accessible.

    • 5

      Drift out the sear axle pin -- located just in front of the hammer -- from left to right using the 2.5 mm punch. Remove the sear axle pin and detent plate. Pull out the disconnector, catch and sear assembly from the top-rear of the frame.

    • 6

      Depress the slide plate, which is located just above the handle grip. Rotate the selector lever up to the 12 o'clock position. Pull out the selector lever. Insert the 1/16-inch punch into the selector-lever hole. Push up and outward to remove the slide plate. Remove the weapon from the vise. Turn the weapon upside down. The slide-plate compression spring will drop out.

    • 7

      Depress the trigger bar until it stops completely and keep pressure on it. Insert the 2.5 mm punch into the sear axle hole. Push the hammer axle out of the hole from left to right. Release the pressure from the trigger bar and pull the hammer out of the frame.

    • 8

      Attach the LEM hammer to the locking piece. The round locking piece will slide into the provided groove on the LEM hammer.

    • 9

      Apply downward pressure to the trigger bar until it stops, and hold it in place. Insert the LEM hammer axle into the axle hole located on the right side of the frame. Align the axle hole on the hammer with the cocking piece and spring. Push the LEM hammer axle into the axle hole from right to left. Release pressure on the trigger bar and guide it up to rest on the LEM hammer axle.

    • 10

      Pull the left side of the cocking-piece spring toward the LEM hammer, and hold it in place. Simultaneously insert the sear and push it down in front of the LEM hammer. Release the pressure from the cocking-piece spring and guide it up to rest against the sear.

    • 11

      Align the disconnector, catch and sear assembly using the 2.5 mm punch; hold the parts in place with the punch. Insert the sear axle into the frame from left to right. Ensure that the sear axle is flush with the frame on the right side.

    • 12

      Turn the frame upside down. Insert the LEM hammer spring onto the hammer strut located on the rear of the magazine well (inside rear of pistol grip). Align the hammer strut with the lanyard-loop insert hole. Push the lanyard-loop insert and lockout mechanism flush with the bottom of the grip. Insert the lanyard-loop insert pin into the hole until it's flush.

    • 13

      Set the frame on its left side onto a bench block. Punch out the trigger axle pin -- located just above the trigger -- using the 1/16-inch punch. Remove the trigger-rebound spring from the weapon.

    • 14

      Turn the weapon right-side up (with the magazine well facing the ground). Push the trigger toward the muzzle. Insert the LEM trigger-rebound spring into the frame using needle-nose pliers. Apply pressure to the spring coil. Insert the trigger axle into the frame from left to right.

    • 15

      Replace the slide and slide-release lever. Rack the slide and pull the trigger several times to ensure proper mechanical function.