LS5 Installation Instructions

Click links below for video installation instructions.

Attaching LS5 Trigger Group to MP5/K

  1. Ensure magazine is removed and weapon is safe.
  2. Remove End Cap and original Trigger Group.
  3. Put the Bolt Carrier in the forward most position.
  4. In the LS5, ensure the Hammer is cocked and the front of the Ejector Lever is down.
  5. Pivot the LS5 Trigger Group onto the Receiver.
  6. Slide the black Buffer tube over the Recoil Spring if you have a Full-Size or Reverse Stretch MP5.
  7. Reinstall End Cap and Push-Pin(s).

Assembly of Trigger Housing

  1. Remove the Ejector Lever retaining e-ring from the Ejector Pivot Pin, then remove the Ejector Lever and white PTFE shim from housing and set aside.
  2. Place the Trigger and Hammer in the housing, then insert the Safety in its hole.
  3. Insert the Hammer Pins. If the Trigger’s cassette has locking set screws, ensure they’re tight.
  4. Install the Safety Detent and Grip with the Safety Spring.
  5. Test Fire Control Group (FCG) for function; Hammer stays cocked in SAFE, Hammer falls in FIRE, Hammer does not fall on Trigger Reset.
  6. Insert Ejector Pivot Pin from the outside of the housing. On the Inside of the housing, place the PTFE shim over the Pin, followed by Ejector Lever and Retaining E-Ring.


Full-Size And Reverse Stretch MP5’s will most likely need to be short stroked to maintain compatibility with the AR15 FCG. This is due to the hammer having a pivot point that is closer to the Firing Pin than the MP5’s original FCG, therefore is shorter. The shorter hammer presents the possibility of the bolt carrier traveling past the hammer, and locking the bolt carrier behind the hammer. The silicone Buffer provides a soft bolt travel limit. The Buffer is not needed in MP5K’s since they have less bolt travel.

Compatible Triggers

Many AR15 and AR10 triggers will work in the LS5 Trigger Housing with modification, and some will work without any modification required. Below is a list of triggers that will drop in:

  • HiperFire EDT line
  • Rise Armament RA-535, Blitz, RA-240, RA-242
  • Ballistic Engineering AR triggers
  • Timney AR15 Competition line
  • Franklin Binary AR

Modifying a Trigger

When getting a trigger to function properly in the LS5 there are two main parameters to meet:

  1. Does the FCG allow proper range of motion for the Ejector Lever?
  2. Does the Bolt Carrier ride smoothly over the AR15 style hammer?

Many drop-in triggers have cassettes that made of aluminum and easily filed to fit under the Ejector Lever.

The hammer can be polished at a 27-30 angle until the Bolt Carrier cycles smoothly.


Printable Instruction Sheet