Lambda Defense Mk48/Maximi notes

[ardrummer292]

One of my guys recently purchased a Lambda Defense Mk48. It survived for about 500 rounds before it blew a piston, which is how it ended up on my work bench. My notes are below, for reference in case anyone wants to take a peek under the hood.

The version my friend got is actually the limited edition “Maximi” version (as used by UKSF), but I imagine there aren’t any significant technical differences between this model and the more common US-issue Mk48 version that Lambda has in production.

 

Externals –

This thing weighs 18-19 pounds unloaded. It’s heavier than my old Echo 1 M240 or CA M249 Para by a wide margin.

Construction is almost entirely steel, including the barrel. I would jump on an aluminum barrel if given the option, just for weight savings.

The barrel release lever’s spring is a little softer/weaker than I’d like. I haven’t had any issues with accidental barrel separation, but I would prefer a bit of resistance from this particular control.

On the UKSF Maximi variant of the gun, the battery is stored underneath the barrel. An 11.1V 2000mAh battery fits perfectly in this space, with a little room to spare for the addition of a MOSFET and fuse.

The bipod is… okay. Better than any other airsoft MG bipod (not counting my old Inokatsu Mk43), but still not as sturdy as the real issue item. I imagine it’s easy to install a real bipod, or at least as easy as doing so on a CA/A&K M249.

The FN-style tri-rail system included with the UKSF Maximi variant is solid, but I’m not sure that it’s the correct rail for a UKSF-issued gun. I was under the impression that a B&T tri-rail with extended side rails was correct.

The ejection port is spring-loaded and actually opens, which is a neat feature. Simply slide it either forward or backward to lock or unlock it. This is handy when arranging wires in the receiver.

The gun feeds from the bottom, which is needed since Mk48s don’t have magazine wells. BBs are routed via a standard feed spring from the ammo bag hanger, up in a sideways “S” pattern, to the bottom of the hopup alignment bracket.

The hopup alignment bracket is an interesting departure from standard CA/A&K M249 designs. Instead of only cradling the bottom of the hopup unit, it completely surrounds it. Be warned that overtightening the two bolts securing the top half of the bracket may lead to the hopup being stuck out of battery, resulting in feeding and/or airseal issues.

The hopup alignment bracket has another peculiar feature. There is a spring-loaded pin recessed in the front face, which locks the hopup adjustment wheel in position. This means the hopup wheel cannot move when the barrel is installed in the gun, which is good for countering loss of setting but fiddly when it comes time to zero the gun.

The charging handle does not need to be retracted (even slightly) for the top cover to close. This is a welcome correction to an annoyance present on basically every airsoft M249 out there.

The safety takes a fair amount of force to engage and disengage, much like the selector on the real thing. Clicks into either position are positive and loud.

The para stock included with the Lambda Maximi is absolutely rock solid. It reminds me of the old G&P para stock, which was similarly sturdy. This is miles ahead of the flimsy CA and A&K para stocks, which snap under a moderate amount of force.

There is a small rectangular cutout on the left side of the receiver, close to where the boxmag mounts, for routing power wires out of the gun and to the boxmag. I think this is an excellent addition, as it eliminates the risk of closing the top cover on said wires and clipping them.

Trademarks are… present. That’s all I can really say about them, since I don’t pay much attention to that sort of thing.

 

Internals –

The gearbox shell itself appears to be an A&K M249 unit. Nothing unusual about it as far as I can tell.

The inner barrel is 460 mm long, and is a standard brass affair with a deep crown at the muzzle. I immediately replaced this with a Prometheus 6.03 mm tightbore in the same length.

The hopup unit is a cast unit, and is proprietary. Feed is from the bottom of the unit. The hopup nub is installed horizontally, much like Bullgear’s upgraded M249 hopup unit; I’m glad Lambda fixed this glaring issue with the legacy CA/A&K M249 platform.

The air nozzle is 21.0 mm long. I have used an SHS MP5K air nozzle as a replacement; while the overall length is the same, the chamfer on the end is shallower. Testing is in progress.

The included cylinder is not ported, and appears to be decent quality. The cylinder head appears to be a Lonex unit, in gold or yellow color.

The stock piston is plastic, with a full metal tooth rack. The stock piston head is aluminum. Angle of Engagement (AoE) is atrocious, which is why this one only lasted 500 rounds before the piston tooth rack snapped in half. I replaced the broken components with a Lonex high torque red piston, Lonex AoE correction piston head, and Lonex hollow piston head o-ring.

The gears are Raptor branded, and appear to be decent quality. There is no sector chip installed to assist with feeding, and SHS sector chips are a loose fit on the stock sector gear.

Bearings appear to be 8mm, but I haven’t pulled them out to check with my calipers.

The motor is a short type, as is expected with this style of gearbox. The stock unit appears to be a ZCI or SHS 16 TPA version, with the relatively high rate of fire to match.

The stock spring appears to be approximately equivalent to an M140.

The microswitch is fairly similar to standard M249 microswitches, but does not use the thin metal arm required by CA/A&K M249 trigger groups. Instead, the Lambda Mk48 trigger group directly engages the button on the microswitch. I consider this an improvement.

The wiring isn’t especially exotic, 16 AWG (ish) for the motor and 18-20 AWG (ish) for powering the boxmag. There is no fuse included. This gun is desperately in need of a MOSFET, especially considering the microswitch is only rated for 15 A and a medium MG tuned to US limits will draw around 25 A (as my Echo 1 M240 did).

 

Box mag –

Externally, the boxmag is a replica of the US-issue 100 rd Mk48 belt pouch: FDE plastic, coyote brown cordura. This is not correct for the UKSF Maximi, which is issued with the FN European-issue color scheme of black plastic and OD cordura.

The cordura cover is secured to the boxmag body via allen screws instead of rivets. I have not yet removed these screws for boxmag disassembly.

Filling the boxmag appears to be accomplished via the ammo belt slot. Dump in however many thousand rounds the mag carries, then replace the black plastic plug and attached 7.62 dummy belt.

The boxmag draws power from the main battery. The 3-wire electrical connection is accomplished via a small black plug of unknown type.

The boxmag operating mechanism is very similar to that used by the Echo 1 M240. There is one pulley attached to a servo (motor), which provides the power. There is another pulley attached to the feeding gear, which spools the bbs into the feed tube. The two pulleys are connected by a rubber o-ring, which serves as a drive belt. I consider this to be a rather poor system, since it is highly susceptible to failure: o-ring gets loose, pulleys get wet, etc.

There are 3 boxmag feed settings, controlled by a 3-way switch close to the pulley arrangement. There is a “constant on” setting, where the boxmag will run as long as it is connected to power. The middle setting is “off.” The third setting is “synch feed,” where the boxmag only feeds when the trigger is pulled.

 

Other notes –

The stock piston blew out at about 500 rounds, likely due to terrible AoE.

The boxmag cannot keep up with the rate of fire, unless set to “constant on” feeding. I will attempt to retrofit a Bullgear Mk48 boxmag insert into the Lambda boxmag to boost the speed of the feed system.

 

Tagging @sniperelite7 so he can share his experience with his Lambda Mk48, if he wants.

[ardrummer292]

3 hours ago, ardrummer292 said:

This thing weighs 18-19 pounds unloaded. It’s heavier than my old Echo 1 M240 or CA M249 Para by a wide margin.

Correction: just shy of 22 pounds (10 kg), with an empty boxmag and no accessories. Brutal.

 

3 hours ago, ardrummer292 said:

On the UKSF Maximi variant of the gun, the battery is stored underneath the barrel. An 11.1V 2000mAh battery fits perfectly in this space, with a little room to spare for the addition of a MOSFET and fuse.

The battery I mentioned here is a Turnigy 11.1V 2000mAh 15-25C LiPO, SKU NG2000A.3S.15. Dimensions are 126 mm long x 21 mm tall x 29 mm wide.

https://hobbyking.com/en_us/turnigy-nano-tech-2000mah-3s-15-25c-lipo-airsoft-pack.html?queryID=ce3dbd784a2df032a85c1c47ac824bcd&objectID=31061&indexName=hbk_live_products_analytics

I'd recommend a battery with a higher C rating (say somewhere in the neighborhood of 20-40C or 25-50C), if possible. I have been unable to find one that fits the bill.

Edited September 21, 2022 by ardrummer292
Correcting and adding information

[E_27_R]

Gonna put my tuppence worth in here as I hounded Lambda until they agreed to produce the Maximi variant and can attest to the similarities (and differences) to the real UK pattern gun. I am by no means an expert on the voodoo witchcraft that makes AEGs function so I’ll stick to the externals.

Externally there are a few fairly significant departures from the UK spec. Lambda was made aware of a couple of these in pre-production but didn’t address them, I’m guessing because of the cost involved. 
I do not mean to detract in any way from the fact that Lambda has brought a unique gun to market in a fairly niche configuration, with some of the most exceptional build quality I have seen on a replica. What follows is mostly nitpicking. I’m very grateful that some manufacturers are paying more attention to the UK scene and my 7.62 Minimi is a prized gun that I have lusted after for many years. 
 

1. The box mag - as ardrummer points out, the box mag provided is a US spec rather than the UK/European pattern. It makes sense that Lambda wouldn’t make a whole new batch of box mags for a very limited run of guns, but I’m told this is on the cards for the future. US boxes are legit for UK guns but I will likely be painting the plastic on mine, adding a plate behind the screws, and dying the canvas. I can’t speculate as to why they opted not to use rivets but that design choice should make it much easier to convert. 
I should also point out that the box mag I received was apparently a revised design with thicker walls - as a consequence, the bipod cannot close properly when the box mag is fitted. 
 

2. The markings - the engravings on the Lambda UK guns is actually pretty spot on. I do have a couple of gripes though. The cocking channel cover provided by Lambda is engraved as per US MK48s - the UK version does not have these markings. Likewise the right hand side of the trigger mechanism assembly features engravings that do not appear on the UK guns. The engravings on the left side of the receiver and the front sight are all correct although I wish they had offered unique serial numbers. 
The engravings on the barrel are also correct although UK barrels should also be marked with the serial number of the gun they are paired with and the barrel number. 
 

3. The rail system is clone correct for the UK guns. The B&T rail is found on the 5.56 L110 guns only. 
 

4. The para stock provided is excellent, by far the best reproduction I have seen on an airsoft gun. Excellent. I cannot comment on the Lambda fixed stock since I haven’t had hands on. Both types are UK clone correct. 
 

5. The stock retaining pins are US MK48 spec. The U.K. guns use old minimi style pins without the holes in the middle. In theory this is an easy fix although finding replacement pins in stock is proving difficult. 
 

6. The barrel latch has lightening cuts that do not feature on the UK guns. In theory this part should be fairly easy to replace. 
 

7. The receiver is riveted rather than welded. This is a little disappointing for me but unless you have spent time with the real guns or have side by side pictures you wouldn’t know. I can’t beat Lambda up on though this since I didn’t labour the point during pre-production. It is built out of steel so this should be fixable in theory, 
 

8. The receiver features elongated lightening cuts towards the front end that do not occur on the UK guns. Also the cut out  in the side of the receiver for the battery wiring - I get that it’s practical but holy f**k is it ugly. I’m still exploring options to fill in some of the lightening cuts and holes. 

9. The gas block has a very shiny finish to it. I’m guessing this is akin to US guns but I have not seen this finish on UK guns. Since I paint my guns this is of little concern to me but it is worth noting. The geometry of the gas block is also incorrect, UK guns have a more square profile rather than the rounded one on the Lambda. This should be fixable although no one would notice. 
 

Ultimately this gun is something of a halfway house. By using existing stock of MK48 correct parts to build something approximating a UK gun has resulted in a piece that is recognisably not a MK48, but also not quite a clone correct UK gun. From a distance, the lightening cuts are the biggest giveaway. It’s only when you get up close that the other departures from UK spec become noticeable. 
The finish and build quality is exceptional and I would highly recommend the Lambda machine guns to anyone in the market. 

[ardrummer292]

Great input @E_27_R, thanks!

 

On 9/25/2022 at 8:27 AM, E_27_R said:

1. The box mag - as ardrummer points out, the box mag provided is a US spec rather than the UK/European pattern. It makes sense that Lambda wouldn’t make a whole new batch of box mags for a very limited run of guns, but I’m told this is on the cards for the future.

[...]

I should also point out that the box mag I received was apparently a revised design with thicker walls - as a consequence, the bipod cannot close properly when the box mag is fitted. 

If Lambda does offer alternate box mags, I think a replica of the shorter 50 round version would be beneficial for many owners. Likely wishful thinking on my part though.

My buddy has not experienced any issues with locking his bipod in the stowed position.

 

On 9/25/2022 at 8:27 AM, E_27_R said:

3. The rail system is clone correct for the UK guns. The B&T rail is found on the 5.56 L110 guns only. 

I didn't realize this was the case. Happy to be corrected!

[E_27_R]

45 minutes ago, ardrummer292 said:

 

If Lambda does offer alternate box mags, I think a replica of the shorter 50 round version would be beneficial for many owners. Likely wishful thinking on my part though.

My buddy has not experienced any issues with locking his bipod in the stowed position.

I’ll suggest the 50rnd boxes but I don’t know that they’ll go for it. I know Lambda have a lot in the pipeline. They are also toying with producing a steel L110A2 but I don’t think there is a timeline just yet. There’s also some talk of an M240 but I think they had some concerns that demand would not be sufficient to justify it. 
 

As for the bipod I’m told it’s a problem with this revised box mag design. The walls on it are apparently slightly thicker which makes it foul with the stowed bipod by about 5mm. Just an unfortunate oversight on the redesign. I can just about get the bipod closed with the mag attached if I push the legs in past the shortest setting, but it’s a very tight squeeze.  
 

[ardrummer292]

Bullgear boxmag upgrade complete, now awaiting testing. Here's some pictures to show a broad overview of the process:

 

Stock boxmag, disassembled. The cordura cover is not shown.

 

Bullgear Mk48 boxmag insert, in stock form. This insert is designed to fit a real Mk48 nutsack, not the Lambda replica. Cutting was required to ensure fitment.

 

Bullgear Mk48 boxmag insert, heavily modified. I cut it to size in order to fit it into the Lambda housing, which involved cutting off two of the vertical "walls," trimming the bottom sliding trap door, and creating a new motor support with a plastic support, nut, and bolt. The 3D printed plastic feed tube was tapped with thread compatible with the coiled feed spring; I didn't do this work, so I'll have to ask what thread spec was used. I also removed basically all of the electronics, leaving only the power leads for the boxmag motor. I intend to wire this up in a parallel circuit with the gearbox itself, leaving the boxmag as a fully slave-powered component.

Edited October 17, 2022 by ardrummer292
Added writeup

[ardrummer292]

A few more picture from the boxmag conversion:

 

Wiring removed from the Bullgear Mk48 boxmag insert. Cutting this wiring out deactivated the adjustable rate-of-fire feature as well as the push-button feed feature. While those are handy, wiring them up was going to be too fussy. A simple on-off arrangement should work just fine.

 

Bullgear Mk48 boxmag insert, cut to size. The sliding bottom trap door is not inserted, allowing you to see the lip at the bottom of the Lambda boxmag body. This will support the boxmag insert quite nicely, while shielding it from impacts.

 

I opted to use simple spade connectors to power the boxmag. There's no need for bulky high amperage connectors (like deans) with such a small motor. I also added a small rubber plug in the wiring pass-through, which should help keep rain out of the boxmag.

Edited October 17, 2022 by ardrummer292

[Jay.Tsao]

On 9/22/2022 at 12:05 AM, ardrummer292 said:

Correction: just shy of 22 pounds (10 kg), with an empty boxmag and no accessories. Brutal.

 

The battery I mentioned here is a Turnigy 11.1V 2000mAh 15-25C LiPO, SKU NG2000A.3S.15. Dimensions are 126 mm long x 21 mm tall x 29 mm wide.

https://hobbyking.com/en_us/turnigy-nano-tech-2000mah-3s-15-25c-lipo-airsoft-pack.html?queryID=ce3dbd784a2df032a85c1c47ac824bcd&objectID=31061&indexName=hbk_live_products_analytics

I'd recommend a battery with a higher C rating (say somewhere in the neighborhood of 20-40C or 25-50C), if possible. I have been unable to find one that fits the bill.

 

[Jay.Tsao]

gens ace airsoft battery with less lower ohm and high C rate. why not have a try for that.

[howitzer]

There is some excellent information in this thread.  Lambda defense  seem a very interesting company, hope they have a stand at the MOA show.

See that on the their Facebook page they are interested in a Negev. Would be a great addition.

As regards air nozzle length variability, that seems to be a case for some support guns. Remember with the PKM, used a MP5K nozzle personally while others had luck with different models such as G3. Seemingly Lonex make a LMG nozzle which is similar in length. Not to sure on  its other characteristics.

Also just to add that Bullgear have their version of the Lambda defense MK48 hop unit on pre-order. So hopefully they expand their line to support the brand.

https://bullgear.net/index.php?route=product/product&product_id=488

Edited November 18, 2022 by howitzer

[ardrummer292]

Got the new WARFET-based wiring harness made up and installed. The gun is a happy camper, especially with the Bullgear insert pumping rounds in as fast as the gearbox pumps them out. Dumped about 1000 rounds through it as a test fire, with no hiccups or drama.

[Turt0416]

Have you had any luck with the hopup units? I currently just rebuilt my Mod 1 (US internals so A&K) and ripped them all out and replaced with upgrades. The gearbox is running very solid but for some reason I am having so many issues with the hopup between trying to jam immediately and almost complete loss of air seal (0.3J or less) any tips you may have on how to get the stock unit to seal would be appreciated! Thanks for all the other info.

[ardrummer292]

6 hours ago, Turt0416 said:

Have you had any luck with the hopup units? I currently just rebuilt my Mod 1 (US internals so A&K) and ripped them all out and replaced with upgrades. The gearbox is running very solid but for some reason I am having so many issues with the hopup between trying to jam immediately and almost complete loss of air seal (0.3J or less) any tips you may have on how to get the stock unit to seal would be appreciated! Thanks for all the other info.

I would check to make sure the hopup bracket inside the receiver is allowing the hopup unit to slide back fully into battery. I found that, if the bolts on the receiver hopup bracket are too tight, the hopup unit will be stuck in a position spaced away from the gearbox.

On 9/21/2022 at 9:02 AM, ardrummer292 said:

The hopup alignment bracket is an interesting departure from standard CA/A&K M249 designs. Instead of only cradling the bottom of the hopup unit, it completely surrounds it. Be warned that overtightening the two bolts securing the top half of the bracket may lead to the hopup being stuck out of battery, resulting in feeding and/or airseal issues.

Edited December 22, 2022 by ardrummer292

[Turt0416]

Yeah I’ve been playing around with that trying to see if I can get it to seat any further but I may just have a lemon Hopup unit. The plastic C Clamp they shipped the hopup with allows the barrel to move forwards and backward a bit, henceforth pulling the bucking with it. I think this may be where I’m losing the air seal due to the vibration of the gearbox itself and that issue. The hopup bracket is only tightened down to where I feel resistance. I wonder if there’s a sweet spot.

[Turt0416]

*UPDATE* thought I’d drop this here to maybe help anyone else out who may have a similar issue. After trying 4 after market 21.00mm nozzles I have finally found that (at least on mine) my hopup unit only likes the stock nozzle and it’s the only way it will work correctly and seal. Perhaps other nozzles will work but the 4 21.00mm nozzles I tried won’t fit due to the diameter of the nozzle and hopup unit. Maxx MP5 21.00mm, VFC MP5 21.00mm and Lonex LMG nozzle don’t fit my lambda. Hopefully this helps those looking to upgrade.

[ardrummer292]

3 hours ago, Turt0416 said:

*UPDATE* thought I’d drop this here to maybe help anyone else out who may have a similar issue. After trying 4 after market 21.00mm nozzles I have finally found that (at least on mine) my hopup unit only likes the stock nozzle and it’s the only way it will work correctly and seal. Perhaps other nozzles will work but the 4 21.00mm nozzles I tried won’t fit due to the diameter of the nozzle and hopup unit. Maxx MP5 21.00mm, VFC MP5 21.00mm and Lonex LMG nozzle don’t fit my lambda. Hopefully this helps those looking to upgrade.

The SHS MP5K nozzle I installed works very well, for the record.

[NevadaZielmeister]

On 9/21/2022 at 6:02 AM, ardrummer292 said:

The hopup alignment bracket is an interesting departure from standard CA/A&K M249 designs. Instead of only cradling the bottom of the hopup unit, it completely surrounds it. Be warned that overtightening the two bolts securing the top half of the bracket may lead to the hopup being stuck out of battery, resulting in feeding and/or airseal issues.

The hopup alignment bracket has another peculiar feature. There is a spring-loaded pin recessed in the front face, which locks the hopup adjustment wheel in position. This means the hopup wheel cannot move when the barrel is installed in the gun, which is good for countering loss of setting but fiddly when it comes time to zero the gun.

Tagging @sniperelite7 so he can share his experience with his Lambda Mk48, if he wants.

First off, I want to thank you for creating this thread. There is such limited information online regarding this new platform. 

The information about the hop alignment bracket was huge. My technician, who was working to upgrade the velocity on my MK48 used this to fix the feeding problems he was having. So I thank you for that as well.

Admins, please don't close this thread. It is filled with very helpful information for us Lambda Defense MK48 owners. 

[NevadaZielmeister]

Does anyone know which bucking I should get to replace the stock one? I am trying to think of wearable items and find replacements. 

[NevadaZielmeister]

On 9/21/2022 at 6:02 AM, ardrummer292 said:

The inner barrel is 460 mm long, and is a standard brass affair with a deep crown at the muzzle. I immediately replaced this with a Prometheus 6.03 mm tightbore in the same length.

Can you give a link for this barrel upgrade? My apologies for not being able to figure it out as the only thing I could find was this one (https://www.evike.com/products/83137/)

 

[NevadaZielmeister]

On 11/18/2022 at 1:02 AM, howitzer said:

Also just to add that Bullgear have their version of the Lambda defense MK48 hop unit on pre-order. So hopefully they expand their line to support the brand.

https://bullgear.net/index.php?route=product/product&product_id=488

I am also very interested in this hopup chamber upgrade. Any idea if they use the same buckings?

[ardrummer292]

19 hours ago, NevadaZielmeister said:

Does anyone know which bucking I should get to replace the stock one? I am trying to think of wearable items and find replacements. 

I’m a fan of Prometheus purple buckings. G&G green buckings are a decent substitute if the Promy isn’t readily available.
 

19 hours ago, NevadaZielmeister said:

Can you give a link for this barrel upgrade? My apologies for not being able to figure it out as the only thing I could find was this one (https://www.evike.com/products/83137/)

 

The barrel you linked is the correct one.

[NevadaZielmeister]

On 1/22/2023 at 4:39 AM, ardrummer292 said:

I’m a fan of Prometheus purple buckings. G&G green buckings are a decent substitute if the Promy isn’t readily available.
 

The barrel you linked is the correct one.

So I tried a Prometheus 455mm barrel and the outer diameter is not allowing the barrel to slide into the outer barrel. I measured the stock brass barrel and it has an outer diameter of 8.47mm while the Prometheus measures 8.54mm. Granted, this is not the exact barrel you reference, in that the one you reference is the Prometheus 460mm AK74MN version. Could there be a difference in outer barrel diameters between the two?

 

 

[ardrummer292]

Prometheus barrels tend to be a bit thicker than others, presumably in the interest of stability and accuracy. I doubt the AK74MN specific tightbore is any thicker than any other Prometheus inner barrel, but I can’t be sure.

 

You might need to lube the new inner barrel so it slides into place. Failing that, I imagine the outer barrel will need to be bored out very slightly. Not sure how that would be accomplished though.

[howitzer]

See that Dave's custom airsoft and Lambda defence are coming out with a M240/L7A2 line.  One interesting point is there is an option for a steel or aluminum barrel.  So the original post is a prescient one as regards the weight saving option.

[ardrummer292]

Does anyone have any information on the new Bullgear hopup unit for these guys? Link:

 

https://bullgear.net/hop-up-lambda-defense-mk48

 

It seems there's some demand for a replacement hop unit, presumably because the stock cast unit doesn't have great airseal. I'm wondering which air nozzle they're designed for.