Modifications:
1. Spring to limit rearward travel – The original housing allowed the Hit Arm to fall too far back and
hang up on the tail of the BCG. This resulted in the bolt getting stuck rearwards. First attempts to
prevent this used a protrusion on the housing, but it ended up needing tuned for each rifle. The
spring fixes the issue without needing tuning.
2. Wire to limit forward travel – The original housing allowed the Hit Arm to swing too far forward, and
wedge under the rear of the firing pin. This resulted in the BCG not being able to move rearward.
3. Material removed from Trigger Locking Bar – On some rifles, the hammer contacts the original
Trigger Locking Bar. Results ranged from causing the BCG to bind and stick as it moves rearwards
(from the hammer applying pressure against it), to functioning properly but just feeling very rough
when cycling by hand.
4. Pin changed from 5.5mm to 5.0mm, which is easier to source.
The SendCutSend files were modified from Fl-Eggs original SCS files to change the pin size and remove material from the Trigger Locking Bar. Simply upload the three files to SCS, choose the right material for each piece (noted in the file name), and click order! I would recommend cleaning up the parts with a file or belt sander to remove burrs, and to round o? the end of the Hit Arm where it otherwise only touches your bolt carrier on the two sharp edges. You’ll need to source some 2mm pins to assemble it with; I’ve been using 2mm x 6mm 304SS pins from Aliexpress. For the housing, I have had no issues just printing it out of PLA, upside down with supports for the pin holes. For the springs, I used METALLIXITY Compression Springs (0.3x3mm OD,10mm Free Length) 10Pcs, 304 Stainless Steel Extension Spring (https://www.amazon.com/METALLIXITY-Compression-Springs-Stainless-
Extension/dp/B0B6J1NX5H), but cut them down to about 1/2 to 2/3 length. I added a smaller hole from the back side that allows you to put some epoxy on a toothpick and apply it to the base of the spring to ensure it stays in place. The spring should stick out a small amount, but if you look from the side you won’t see it sticking out the top, so there is no risk of it getting hung on the carrier during operation. If it is sticking out a bit far, you don’t necessarily need to cut more o?, just use a pick to push it further in before epoxying. To limit forward travel, place a piece of paperclip through the holes at the front of the housing and bend the ends into the slots to keep it in place. The hit arm will rest against it in the forward position and prevent it from going past 12 o’clock.
I order stainless 5mm rod from Amazon for the main pin, any should do once you cut it to 0.438” (or slightly less).
I’m also including a couple of modified versions of the Dissident V1.1 selector in this file set. I found that it didn’t sit flush on the selector side, so I shortened it a bit, and then I added a hole that is sized to thread in a 6-32 machine screw as a reinforcement. Use a 1” long 6-32 machine screw for the normal selector, or a 1.25 for the
ambi.

Leber V2AR15 FCG Based MP5 Lower

Description

The Leber V2 is an AR-15 Fire Control Group (FCG) trigger pack compatible with SP5, SP5K,AP5, and AP5-P. It uses bent sheet metal to retain the hammer, trigger, selector, and ejector.The steel plates interface with the receiver at the front and back, removing all stress from thepolymer external housing. These steel plates allow for a flush external polymer housing,giving the Leber V2 a more factory HK trigger pack appearance while also being muchstronger. The lower also features a built-in grip option to mirror the factory HK trigger packgrip, which significantly improves durability.Credit to @UberPoor on X/Odyssey for the ARMP5 V1 & V2, as the Leber V2 was heavilybased on those early designs.For those interested in supporting future projects, donations are greatly appreciated.Contributions can be made via Bitcoin to the following address:bc1qz37yzsa6090alxd5zlulhm3ns38qjrmszcq2c5
Send Cut Send Plate DisclaimerSendCutSend, while a great service, isn't perfect and has a success rate of about90% when it comes to bending and cutting the plates accurately.Due to this, you need to understand that there is a chance you might receive aplate that is so far out of spec that it is not salvageable. Normally, they will replacethe plate when this happens, but this is something you will want to be aware of.I have spent a lot of money and time trying to ensure these plates can be made tofairly loose specs and still function, but sometimes they are just so far out of specthat there's not much you can do to save them.Finally, it is also very important that you order the plates correctly. Due to thecomplexity of these plates, you need to ensure each bend is correct in the SCSinterface, as well as make sure you have the standoff in the correct hole andfacing the correct direction.
MP5 Ejection Guide
Failure to eject (FTE) is the most common issue that arises when using AR-15 FCG
lowers. This is due to the added pressure of the AR-15 hammer and the force required
to reset the super safety cam. Both of these require significant bolt carrier energy.
That said, this is an easy issue to fix as long as you know what to look for and are willing
to spend a small amount of money on quality parts.
MP5 extractor spring:
The MP5 extractor spring is the weakest part of the MP5
design and can be easily damaged, resulting in FTE. I recommend replacing your
bolt face with an RCM MP5-E bolt face or regularly checking your extractor spring
stiffness.
Locking Piece:
The MP5 locking piece is the most common cause of FTEs. The lower
the degree of the locking piece, the less bolt carrier energy is available, increasing
the likelihood of FTEs. This issue can be resolved by using a locking piece with a
higher degree (no higher than 100 degrees unless using 115-grain ammo). RCM
locking pieces are recommended.
Ammo:
Using the wrong locking piece in combination with certain types of
ammunition can result in FTE.
AR-15 Hammer:
The AR-15 hammer requires more force to reset than the factory
MP5 hammer. While this is perfectly functional, if you want to improve reliability
with weaker ammo types, the Geissele SSA-E FCG is compatible with the Super Safe
Leber V2 and is much easier on the bolt carrier. It also requires less force on the
trigger, making resetting the cam easier as well. A reduced AR-15 hammer spring
might also help; however, if you encounter light primer strikes, it may be too weak.
Ejector Lever:
This is one part you should never skimp on. Spend the money and
buy a quality, genuine German GEN 3 ejector lever. This lower was designed around
this ejector lever; using anything else is setting yourself up for failure.
Examples
115-grain 9mm with a 90-degree locking piece and no suppressor attached
will likely result in FTE on every shot. (Switch to a 100-degree locking piece.)
124-grain 9mm with an 80-degree locking piece and no suppressor attached
will likely result in occasional FTEs. (Switch to a 90-degree locking piece.)
Non Printed Parts List
Send cut send plates
-
1x Send Cut Send MAIN FCG Plate
-
1x Send Cut Send BACK Plate
Ejector & Ejector spacer
-
1x 6 mm OD, 4 mm Long 4.2 mm ID, Spacer
McMaster Link
-
1x Factory German HK Ejector with the cut for the hammer
(Using anything other then a HK ejector will not work)
-
1x German Ejector Spring (Optional but recommended to stop wobble)
Detent Set screw
-
1x Flat-Tip Set Screw 18-8, M5 x 0.8 mm, 12 mm Long
McMaster Link
Plate Retaining
-
1x M5x20 Socket Head Screw
-
1x M5 Nut
Standard AR15 FCG
-
Standard AR15 Hammer /
Heavy
Hammer Spring
-
AR15 Trigger / Trigger Spring
-
AR15 Disconnector / Disconnector spring
-
AR15 Selector / Selector detent and spring
-
Trigger Pins (A hammer and trigger pin)NOTE: Using non-standard hammers may change the buffer size needed. If youdon't want to use a buffer, you will need to file your hammer so that the BCG cannotget stuck behind it.The Leber V2 was designed around a standard Hoffman-spec cut Super Safetytrigger. This means no custom modifications are required for the Super Safety tofunction correctly. Any pre-cut trigger will also work properly with this lower,provided it has been cut to the correct specifications for AR-15s.
Ordering Send Cut Send PlatesStart by uploading the SCSMAIN FCG Plate. Do not dragand drop the file; instead, clickthe upload button and select thefile manually.Next, select the material by clicking (Metal > Steel > G90Galvanized > .074" (1.9MM)). Ensure you select the correctthickness, as an incorrect selection will affect the part's fit orfunction. Once selected, click Done, and then proceed to Next.Now select the Bend tab on the Add Services page and verify that all your bends are correct.Ensure the 3D model matches mine (the yellow warning is normal). Once confirmed, click Done.
This step is the most commonly messed up, so ensure you select the correct standoff for thecorrect hole and that it is facing the proper direction. (Flush Standoff, M3 x 0.5, .236")After clicking "Apply," you might notice that the standoff is facing the wrong direction. Be sure toclick the arrow to adjust it so that the standoff faces outward from the FCG. Refer to the imagebelow for guidance. The menu will lag be patient. This is what the finished part should look like. Carefully review the 3D model now to ensure itmatches mine. Send me a picture like this and i will verify if you did it correctly.
Now, for the back plate,select either Full Size orK Size, depending onwhether you have a full-size MP5 or a K model.For the Full Size BackPlate, Make sure toselect .048" (1.2MM).Then click Done andproceed to Next.
For the
K Size
back
plate, make sure to
select
.074" (1.9MM)
.
Then click Done and
proceed to Next.
For both plates, the correct bend angle is 90 degrees. You may see two yellow
warnings, but this is normal. Ensure both bends are facing the same direction.
Send Cut Send Plate QC CheckDue to the complexity of the FCG plate and the potential for SendCutSend tooccasionally produce out-of-spec parts, this printable jig is provided to checkand verify that the plate are in spec.You can print the QC jig at0.15mm layer height. You mightneed to drill the selector andtrigger / hammer pin holes out.The jig can be inserted fromthe front; it may be a tight fit,but if it does not fully seat,the FCG plate is out of spec.
Once the holes are properly
aligned, you can insert the trigger
and hammer pins, and the
selector should slide in smoothly.
Print settings and orientationAll STL files are oriented correctly and include built-in supports where necessary. Thebuilt-in supports can be separated in the slicer and printed with a lower infill to reducematerial usage, if desired. (STEP files are not oriented correctly.)Ensure that your printer is calibrated for the filament you are using, as failure to do somay result in the plates fitting too tightly. It is also crucial to follow the settings belowto ensure proper fitment and to guarantee that the built-in supports function correctly. - Temp: 220/60C (Polymaker PLA Pro) - Nozzle: 0.4mm - First Layer Height - 0.20 (Or 0.15) - Layer Height - 0.15 - Wall Loops - 8 Walls Max - Infill - 100% RectilinearFor nylon printing, see my guide on Odysee @s3igu2 for Polymaker PA6-CF.
Printed Parts ListFor the housing, you willneed either the K or full-size housing. Make sure topick the correct housing, asthey both look very similar.(FULL SIZE MP5 ONLY) Next, you need a 48mmTPU buffer to prevent the BCG from slippingbehind the AR-15 hammer and getting stuck. Theonly situation where you don’t need the buffer iswhen using a full-auto sear with a true full-autoFCG, or if you cut your hammer to avoid needingthis buffer. (Print in TPU95A 100% Infill)
The ejector cutting jig is used to cut the ejector
in such a way that the hammer no longer stops it
from going flush. Improperly cutting the ejector
will cause various issues, primarily preventing
the charging handle from being pulled back.
The selector detent extender bar goes into the
detent track after the detent and detent spring,
filling the gap so the set screw can apply pressure
to the detent spring correctly.
The Super Safe Ramp prevents the lever from
dropping below the reach of the slip trip. Even if
you aren't using the super safety, you will still
need this ramp unless you use a shorter M5 screw.
The Slip Trip is required for the Super Safety
to function with this lower. If you do not plan
to use the Super Safety, then you will not
need the Slip Trip. You can download the
latest version of the Slip Trip on my Odysee.
https://odysee.com/@S3igu2
Using a 1/8-inch drill bit, drill this hole from
the top of the lower. Make sure you don’t drill
too far into the detent track. You should only
be drilling about 6mm deep into the hole.Drilling the selector and detent holeThis transparent lower shows the detent track and illustrateshow to avoid drilling too deeply. The drilling depth ishighlighted in blue. At this stage, you will also need to drillthe selector hole to 3/8 inch.
Ejector Cutting Jig Guide Place the ejector into the jig like so,ensuring the hole in the middle is lined up.Mark the ejector with a Sharpie then remove theejector from the jig. Cutting it with the jig on works,but it will melt the jig pretty quickly.Cut the ejector where marked with a Dremel or another tool,ensuring you end up with a cut like this. You can also sandand smooth the edges to make sure everything fits properly.
Nut, Rear plate and Ejector spring installInstall the M5 nut into thecutout at the back of the lower,ensuring the nut is sitting flushand not sticking up.Now, slide the back plate in. TheK plate should sit flush with theback wall. The plates may needto be adjusted to align with thepin hole. Use a rubber mallet ifthe plates are too tight. If theystill won’t go in, then your printsettings are likely off.Install the ejector spring into thehole highlighted in blue. Thespring should drop in easily; if itdoesn't, make sure nothing isblocking it in the hole.
Main SCS Plate AssemblyInstall the hammer, trigger, anddisconnector into the main SCS plate,just as you would in a normal lower.Now, install the spacer ontothe standoff, and then placethe ejector onto the spacer.The FCG is now ready to beinstalled into the housing.
The ejector will be loose on
the plate, so make sure to
hold both the ejector and
spacer in place until it's in
the housing.
Main SCS Plate InstallWhile holding the ejector onto the plate, insert thefront of the main SCS plate into the housing first,allowing it to slide under the front tab of the housing.
The main FCG plate has a front lip that
needs to be slid into this front cutout
first. This front lip on the plate will sit
on the shelf of the SP5 receiver.
You will need to push it down and forward; eventually, it
will snap into place. This might take a bit of practice, but
it should be fairly easy once you get the motion down.The most common area to be out of spec with the main send cut-send plateis the selector hole. It should line up almost perfectly with the selector holein the housing. If you notice the selector won't go in, make sure to push theFCG forward or backward so the plate lines up with this hole.
Selector InstallNow, install your selector. This shouldbe done the same way it would bedone on an AR-15 lower.
Drop the detent, spring, and set screw into thehole at the bottom of the housing. Then, insertthe selector detent bar and tighten until the setscrew is flush with the bottom of the grip base.Selector Detent Install
Ramp and M5 Screw installPlace the ramp into the cutout of the housing.
Thread the M5x20 socket head screw
into the ramp. Do not overtighten this
screw; just get it hand tight.
TPU Buffer install Full Size MP5 OnlySlide your 48mm TPU buffer onto the recoil spring and installthe lower as you would any other MP5 lower.
Function checking the lowerAt this point, verify that the ejector moves freely up and down without anyresistance. This step is crucial, as a sticking ejector will cause failures to eject.Additionally, you can now perform a function check of your FCG in both semiand Super Safe modes while it is off the receiver. Be sure to catch the hammerto prevent it from slamming into the polymer housing.When testing a brand-new lower with live ammunition, it is highly recommendedto start with a few mags of 124-grain NATO rounds, a 90-degree or 100-degreelocking piece, in semi-auto mode only, and without a suppressor.Make sure to follow the slip trip documentation if using the super safety.
In some cases, the back of the housing mayneed to be filed down. This depends on thestock or brace being used.Housing FitmentThe plates are designed to be pushed forward orbackward when the M5 screw is loose, ensuring theholes line up with the receiver.
Troubleshooting
Failure to eject:
See the ejection guide at the top of this document.
Light primer strikes:
Verify that your hammer spring is correctly installed and
not backward. If that's correct, you can switch out your hammer spring for a new
one or upgrade to the heavy hammer spring.
Bolt carrier stuck in the back of the upper:
Verify that your 48mm TPU buffer is
installed over the recoil spring. Also, avoid using non-standard AR15 hammers,
as this will require a different buffer size or modification to the hammer itself.
Send cut send plates are hard to install:
This is usually a good sign that you are
printing well out of spec. Instead of sanding or banging on the plates, you should
investigate why this might be happening with your printer and adjust settings.
Feeding Issues:
If you encounter feeding issues, I recommend using high-quality
magazines such as genuine HK magazines or KCI Gen 2s. If failures persist, try
replacing your mag catch with a genuine HK mag catch.
Back plate wont seat all the way in:
Ensure there is no support structure in the
track of the lower housing where the back plate slides in. Any support structure
in the track will prevent the plate from being fully inserted.
Hard to remove support structures:
If the support structures are difficult to
remove, firmly tap on them or use pliers to dislodge them. They may feel stuck,
but they should pop off with some force. A 0.15mm layer height is required for
the support structures to remove correctly.
Loose / Wobbly ejector:
Make sure you are using a genuine German HK ejector
as other manufactures will not work correctly with this lower.
Stuck selector detent:
If the hole has been properly drilled out to 1/8 inch and
the detent is still stuck, you will need to push it out from the top using some
filament. I just break a few inches off a roll of filament and use that. Ensure that
no supports are being generated in the detent track, as these will also need to
be cleared.
Lower retainer pins are tight:
This can happen when the back plate is not
aligned correctly before being tightened down. The back plate is designed to be
adjustable, so make sure it is lined up with your upper's holes before tightening
the screw.

Introduction If you own an HK MP5 .22LR and want better trigger reset performance, you’ve likely looked into forced reset triggers (FRT). This guide explains how an FRT functions in the MP5 .22LR, what makes this platform different, and what you should expect during installation and tuning.

What Is a Forced Reset Trigger (FRT)? A forced reset trigger is a mechanical part that actively pushes the trigger forward after every shot. Unlike a normal semi-automatic trigger that depends on the shooter releasing pressure to reset, an FRT uses the gun’s cycling action to reset the trigger. This allows faster follow-up shots while still delivering one shot per trigger pull.

How It Works in the HK MP5 .22LR Platform The HK MP5 .22LR uses a different fire control group layout than most AR-style rifles. Key differences include:

• Unique trigger bar geometry
• Different overall trigger group design compared to centerfire platforms
• Much more limited aftermarket support

In this setup, the FRT interacts with the trigger bar as the bolt cycles, forcing the trigger forward during the reset phase. Because of these platform-specific traits, proper fitment and tuning are more important than on standardized platforms.

Is It a True Drop-In Part? (Short Answer: No) This is not a simple plug-and-play component. Most installations require:

• Minor fitting and adjustments
• Careful positioning to ensure reliable function
• Fine-tuning for consistent performance

Results can vary between individual firearms, so testing on your specific gun is essential.

Why Having Multiple Units Helps Many owners like to keep extra units on hand for:

• Testing different fitment options
• Experimenting with positioning
• Dialing in performance before final installation

This is why packs with both single units and multiples (including steel and PET-CF versions) are popular.

Material Options: PET-CF vs 316 Stainless Steel

PET-CF (Carbon Fiber Reinforced Polymer)

• Lightweight
• Easy to modify and adjust
• Great for initial testing and dialing in fitment

316 Stainless Steel

• Highest durability for long-term use
• Excellent wear resistance
• Best choice once fitment is perfected

Most users start with the PET-CF version to fine-tune everything, then switch to steel for permanent use.

What to Expect During Installation Installing and tuning an FRT in the MP5 .22LR requires:

• Basic mechanical knowledge
• Patience and careful adjustment
• Willingness to test and tweak as needed

There is no universal “one-size-fits-all” method due to small variations between guns. Common adjustments include:

• How the unit contacts the trigger bar
• Retention method tweaks
• Final positioning for reliable resets

Safety and Responsibility Always follow these rules:

• Practice safe firearm handling at all times
• Fully test the installation before live fire
• Comply with all applicable local, state, and federal laws

Incorrect installation or use can lead to malfunctions or injury.

Final Thoughts The HK MP5 .22LR forced reset trigger setup is a specialized option for users willing to invest time in proper fitting and tuning. It’s not plug-and-play, but when done correctly it delivers a fast, consistent reset.

Available Options

• HK MP5 22LR STEEL FRT SINGLE
• HK MP5 22LR STEEL FRT 2 PACK
• HK MP5 22LR PET-CF FRT SINGLE
• HK MP5 22LR PET-CF FRT 5 PACK