Lee Sporting reached out to us to see if anyone at TFB would be interested in checking out their Sporting Trigger Group for the MP5. As an ardent fan of the MP5 platform, I volunteered as tribute. Lee Sporting has made their Sporting Trigger Group utilize an AR-15 FCG (Fire Control Group) which has secondary ergonomic benefits. So let’s take a closer look at this cool upgrade for you MP5 afficionados.
Lee MP5 Sporting Trigger Group
As I said above, the Lee Sporting Trigger Group uses an AR-15 FCG for the trigger and hammer. They designed the trigger housing to use AR pistol grips and safeties. It still uses an MP5 ejector but they had to modify it a bit to fit with the trigger cassette.
Lee Sporting uses a Rise Armament trigger which has a 3.5 lb trigger pull. If you notice, the cassette has been modified as well to make room for the 9mm ejector.
Here is the Lee Sporting Trigger Group next to my German HK factory trigger group. The Sporting Trigger Group came with a Magpul MOE K grip but I swapped it out for an HK 416 pistol grip.
The Sporting Trigger Group is noticeably lighter than a standard HK trigger group. This is due to the fact you do not have a steel cassette anymore and just an AR trigger and hammer. Even with the Rise Armament cassette style trigger it is lighter.
Better Ergonomics Thanks To Science!
Because the Sporting Trigger Group uses an AR FCG, the trigger and hammer sit higher and more forward than the HK trigger and hammer. This also allows the pistol grip to be more forward and higher. See the photo below. I superimposed the factory trigger housing over the Lee Sporting Trigger Group so you can see how much of a difference it makes.
Since your fire control hand is more forward and higher up, the MP5 or in this case my SP5, feels better to hold. My hand is closer to the CG of the gun so it balances better in the hand.
The Lee Sporting Trigger Group comes with an extended mag release for the paddle since the trigger guard sits a little close to it. I was unable to use the magazine paddle release extension since I use a Haga Defense flared magwell. See the photo below. The screw for the magwell interferes with the operation of the magazine release extension.
The trigger guard sits a little too close but you can still engage the paddle release if you had to. However there is a better way, with science!
Since your hand position is now more forward and higher up, you can reach the side magazine release with ease like an AR-15 magazine release.
Improving The Sporting Trigger Group
When I got the Lee Sporting Trigger Group, I was eager to try it out. Well, I had a malfunction when I first tested it. I fired about 10 rounds and the gun locked up. I took it off the line and found the hammer had fallen in front of the bolt. I pulled the end cap off, removed the recoil spring and bolt so I could reset the hammer. But when I tried to drop the bolt in place, the natural resting position of the hammer is too high so I had to pull the lower off, install the bolt and then reinstall the lower so the hammer rests up under the bolt.
I contacted Lee Sporting and over the phone we figured out the issue. Lee Sporting tested this using an SB Tactical HK PDW brace and it has a rather thick buffer in the end cap. I am using the Magpul Brace and the buffer pad is relatively thin. Lee was then going make thicker buffers to include with their triggers but the problem would be how thick would they have to be? And would they need to be different thicknesses for various endcaps? Then I remembered my HK91/G3 .22LR conversion kit. I recall reading about a hack HK91 users would do to prevent bolt-over-travel with the .22LR bolt. They would add a length of rubber tubing over the recoil spring which would prevent the bolt from going too far back and allowing the hammer to fall in front of it.
I went to Ace Hardware to get some vinyl tubing to try this solution while Lee Sporting sourced a better material which they now include with their lowers. I tested the malfunction and filmed it with my Chronos 1.4 slow motion camera. Then filmed it again with the vinyl tubing buffer fix. Success. No more bolt overtravel issues.
Here is the tubular buffer that Lee Sporting will provide with his trigger group.
Lee Sporting’s trigger group is 3D-printed. Nothing wrong with this as we have seen other manufacturers use 3D printing to make MP5 furniture and even night vision goggle housings. Because it is made with additive manufacturing, it is easy and relatively inexpensive for Lee Sporting to implement design changes. With some feedback from me, Lee Sporting has already tweaked their design. See the images below.
Lee Sporting changed the shape of the trigger guard to make it easier for people to access the paddle mag release in case you still want to use it. They also added a slot for a nut. Before the grip screw threads were printed and chased with a tap to clean them up. However, I already stripped some of the threads in the sample they sent. I told Lee Sporting how FN has a slot and square nut in their SCAR trigger housings. No need to rely on polymer threads. Now you have metal on metal contact.
At this moment, Lee Sporting are having their own ejectors made. They have found inconsistencies in the USA-made ejectors. Their redesigned and higher tolerance manufactured ejectors will no longer require to have the trigger cassette to be modified nor the ejector itself.
Another direction to take the Sporting Trigger Group is to make it work for the HK91/G3 style firearms. Sadly, it does not work in its current configuration for two reasons. The .308 ejector won’t work and the AR hammer locks up the bolt.
See the photo below. The bolt and carrier have a gap. When the bolt travels rearward the corner of the hammer will push up into that gap. Causing it to catch on the front of the carrier thus locking up the action.
The hammer issue is a bit harder to solve. Lee Sporting is looking into different hammers or possibly modifying them with a curve so they do not lock up. Meanwhile, a .308 ejector does not quite fit in the Sporting Trigger Group. This will be a slightly easier fix since they just have to change the trigger housing to accommodate the larger ejector.
Final Thoughts On The Lee Sporting Trigger Group
I like it. The ergonomics are noticeable and being able to press the right side mag release is awesome. Unfortunately, this is not as big a deal if you shoot an MP5 left handed. At $425, it is not cheap but reasonably affordable if you like better ergonomics and a single-stage 3.5-pound trigger. Plus it uses AR pistol grips so you can change it for any grip you like.
A common question I was asked was “can you add a third pin or use a forced reset trigger?”. The answer is you could but it would not work. An M16 sear requires a full auto AR carrier to trip it. Same with a forced reset trigger. You would need to find a way for the MP5 bolt to trip that reset or sear. Could you put a binary trigger in this? Yes but considering a binary trigger for an AR are just under $400, you would have spent over $800 to have a binary in an MP5. You could just buy the HK BFSIII binary trigger and drop it in your factory trigger housing for under $700. Plus you do not have any issues with outrunning the trigger like you can on an AR binary trigger.
Right now the Sporting Trigger Group fits semi auto shelfs like the H&K SP5 and PTR clones. I am not sure if it will fit the two-pin shelf MP5 clones like the MKE variants as I no longer have access to one and Lee Sporting has not tried either. I want Lee Sporting to make a version for the MP5K which should not be too difficult. I would also like them to offer their trigger group unbuilt for a lower price so you can built it how you want with any trigger you desire. For more information or to order a trigger group for your MP5, check out the Lee Sporting website.