Have you read the instructions? We know... But please read the instructions for helpful videos and written steps for installation and trigger modification.

Have you installed the buffer tube? 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.

Have you installed the shelf insert? Semi-Shelf LS5's come with 2 different shelf inserts to fine tune the fitment of the LS5 to the MP5 or MP5K receiver.

Ejection issues? After significant testing we found that replacing the extractor spring and/or the extractor bolt in some MP5's helps to resolve ejection issues. We suggest the HK MP5 Spring and the RCM MP5-E Bolt. We have seen cases where brand new MP5s have faulty springs within the first few hundred rounds. 

Smooth cycling issues? Some hammers need a 27-30 degree chamfer on the top front of the hammer. This will allow the bolt carrier to cycle smoothly on top of the hammer.

Super safety issues? Please note, dry firing and manual function testing in a MP5K DOES NOT work when testing a super safety. To function test a MP5K with a Super Safe setup will require the end cap/stock to be removed to actuate the Super Safety.

How do I install an Atrius FRS in an LS5?

1. Install your LS5-ACI into the rear of the trigger pocket.
2. Insert Atrius Detent Shaft through the right side of the LS5 about halfway into the receiver.
3. Install the Spring and Cam-Lever before pushing the Detent Shaft all the way through the LS5. Ensure that both the left side switch and the right-side indicator/switch are both in the same firing position.
4. For video instructions skip to the 1 min. mark in this video by Atrius.

Please refer to the trigger compatibility section in our installation instructions for fitment guidance. We currently recommend the ALG-ACT trigger for your FRT build.  You will also need to install a slip trip to allow the Atrius FRS to function. 

If you ordered the wrong variant, please use the contact page and let us know ASAP and DO NOT REORDER. We can update your order in our system to avoid any unnecessary fees.

FAQ

Where is my order?
When your order is ready to ship, you will receive an email with tracking information. Please refrain from emailing us and asking for order updates. All of our products are produced according to variable manufacturing schedules. As a small business, we work closely with other small suppliers, which limits how quickly we can produce, assemble, and ship orders — we are not a same‑day fulfillment service. Orders are assembled in the sequence received and depend on current part availability. Built Lee Sporting Trigger Groups, Cerakote orders and special requests require additional time and will ship later than other items on our site. Thank you for your patience and support.

I purchased an LS5 from another retailer and I'm having issues, what should I do?
If you have previously purchased an LS5 trigger group from another vendor, please reach out via our contact page and we will do our best to get you squared away! 

Do your trigger groups include a buffer, or do I need to buy it separately?
Our Full-Size LS5 trigger groups include a durable, high-temperature silicone buffer, so no separate purchase is necessary.

Are modifications required for Geissele triggers when used with an LS5?
Yes, slight chamfering (approximately 27-30 degrees) on the hammer is necessary for optimal fit and function. Our Trigger Group options come with the Geissele trigger already modified. 

How can I order replacement parts, such as buffers or shelf inserts?
For replacement parts, Click Here

Can I use a Hoffman Super Safety with an LS5?
Yes! However fine tuning may be required with the added complexity.  Ensure that the slip trip cycles freely in the receiver, and the bolt carrier rides smoothly over the hammer.

How do I install a Super Safety in an LS5?
Watch this instructional video

Can I order an LS5 with a Super Safety?
At this time, no. We do not currently offer super safety trigger groups for purchase. Instead, check out our complete trigger groups with the Atrius FRS.

What LS5 variant do I need for my HK SP5?
You'll need the Full-Size Semi-Shelf LS5 lower receiver for your HK SP5. If you are curious about other variants and compatible MP5s, Click Here

Does the LS5 Trigger Group fit to HK53 or HK91 style guns?
Almost, but no. The LS5 uses a proprietary ejector lever. 223 and 308 ejector levers are in the works. 

Which grip should I buy?
Check out our detailed description page on our selection of grips here.