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Echo 1 M240 review (kinda)

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Hey all, figured I should finally get around to sharing this outside of my little group. This is something I wrote up to help people build a Medium Machine Gun (MMG) for Milsim West events here in the US. It's all very NATO-centric since I'm part of the UK forces contingent (no PK-series gats covered here, sorry). This article is half UK-issue L7 GPMG build guide and half Echo 1 M240 review. Lots of technical details in there! Hopefully someone will find it useful.


L7A2 GPMG build guide



Why should you build a Medium Machine Gun (MMG)?

  • In the military, MMGs are the primary casualty-producing direct fire weapon.

  • In airsoft, properly employed MMGs are the primary casualty-producing direct fire weapon.

  • Basically, they are really good for killing a whole lot of mother*fruitcage*ers from outside the range of regular rifles and Light Machine Guns (LMGs).


Why shouldn’t you build a MMG?

  • They can be a pain in the *albatross*, both due to size/weight as well as technical intricacy.

  • If they aren’t set up properly, they’ll be unreliable garbage.

  • You can’t be an assaulter with a MMG, getting breachy-freaky with the lads. You’ve got a Minimum Engagement Distance (MED) to obey.


UKSF-legit MMG options

  • The only kosher MMG available to us is the L7A2 GPMG, which is a derivative of the FN MAG (or in American parlance, the M240).


Base gun options

  • HPA systems

    • Don’t do it

    • You could carry 3 batteries in your pocket good for at least 15k rounds, or you could carry a big *fruitcage* air tank good for the same amount. Keep in mind that this is in addition to all your other kit.

    • Don’t be dumb, keep it electric.

  • Inokatsu

    • Pro

      • Real weight (25ish pounds)

      • 1:1 dimensions, so compatible with real external parts

      • Supplied with excellent quality (basically real) external parts

      • Mega *fruitcage*off CNC machined brick of a gearbox with no known compatibility issues

    • Con

      • Real weight (25ish pounds)

      • Been discontinued since 2011

      • Expensive as *fruitcage* ($1800+)

      • *suitcasey* design makes it unreliable and generally an awful performer

      • *fruitcage*in impossible to get spare gearboxes or box mags

    • Verdict: basically only good as a display piece, not worth it

  • Trigger Happy

    • This is the only M240 out there that I don’t have hands-on experience with.

    • Verdict: it’s a less refined version of the Echo 1. I wouldn’t buy one.

  • Golden Eagle/JG/Matrix

    • Pro

      • Easy to obtain

      • Reasonably priced ($500 or less, usually)

      • Lighter weight (16ish pounds)

      • Nearly 1:1 dimensions, so compatible with most real external parts

    • Con

      • External parts are made of cheese; as such, they disintegrate with very little force

      • Gearbox has weird compatibility issues, specifically with pistons and sometimes gears

      • Difficult to get spare gearboxes

      • Doesn’t come with a MOSFET as standard

    • Verdict: utter trash, wouldn’t touch it with someone else’s 10 foot pole

  • S&T/Lancer Tactical

    • Pro

      • Decently-executed clone of the Echo 1 M240

      • Easy to obtain

      • Reasonably priced ($600 or less, usually)

      • Lighter weight (16ish pounds)

      • Comes with a MOSFET stock (usually)

      • External parts are much better quality than the Matrix offering

    • Con

      • Not quite 1:1 dimensions, as the receiver is 1-2mm shorter than the Matrix, Inokatsu, and real versions

      • Gearbox takes a semi-proprietary piston with no reinforcing side rails running alongside the tooth rack; everything else seems to be standard parts

      • Difficult to get spare gearboxes

      • Stock MOSFET isn’t great quality

      • Externals are okay quality, but some parts (the bipod, specifically) will eventually break

    • Verdict: not bad, but not that great either. A decent alternative to the Echo 1 offering.

  • Echo 1

    • Pro

      • The most popular version of the M240, and with good reason

      • A partial clone of the Trigger Happy M240, which was one of the first airsoft M240s

      • Usually reasonably priced (around $500 on the used market)

      • Lighter weight (16ish pounds)

      • Gearbox has very few compatibility issues (only the air nozzle is proprietary)

      • Comes with a MOSFET stock

      • Externals are actually decent. Nowhere near as good as the Inokatsu or real deal, but pretty damn good regardless.

    • Con

      • Been discontinued for a few years, so hard to find

      • Not quite 1:1 dimensions, as the receiver is 1-2mm shorter than the Matrix, Inokatsu, and real versions

      • Difficult to get spare gearboxes and box mags (S&T box mags *should* be compatible)

      • Stock MOSFET is decent, but isn’t bombproof

    • Verdict: this is as good as it gets, in my experience. Find one (or two) and buy it.

I chose the Echo 1 M240B as my base gun, since it has maximum aftermarket compatibility with internal parts. This is pretty important since machine guns break *suitcase* all the time.




Individual equipment

  • Load bearing

    • PLCE belt kit, in DPM, standard rifleman configuration

      • 2 mag pouches on both left and right sides

      • 3-4 utility pouches in the middle

    • Ops vest, in DPM

      • Less legit than a PLCE belt kit for GPMG gunners, but still usable

    • MOLLE belt kit, in OD

      • Set up with Blackhawk OD pouches plus DPM PLCE pouches as you please

  • Armor carriage

    • Paraclete SOHPC

      • Only for use with belt kit

      • Keep it almost entirely slick, with maybe an admin pouch

    • Kandahar plate carrier, Blackhawk low vis plate carrier, or Blackhawk helivest

      • Worn over belt kit yoke or under ops vest


External gun modifications

  • First things first, don’t dump money into externals until you know the thing will run reliably. Getting  your gearbox and boxmag squared away is priority.

  • Bare minimum

    • Get a MAG58 flashhider from Ohio Ordnance Works and get a machinist to mount it

    • Remove the rail from the top cover

  • A little more legit

    • MAG58 flashhider, as above

    • Replace the top cover with a real M240 unrailed top cover (will take some grinding to fit the Echo 1 or Lancer Tactical/S&T M240)

    • Source a UK-issue 50rd jungle tin and convert your boxmag to fit

  • Pretty legit

    • All of the above

    • Have the gas block ground down to L7 spec

    • Get a MAG58 gas regulator from Ohio Ordnance Works and get a machinist to mount it

  • Really legit

    • All of the above

    • Source a L7 ribbed carry handle and buttstock/buttplate

  • Maximum legitness

    • All of the above

    • Source a C2 sight mount and fit it to the left side of your receiver

    • Source an issue L7A2 height adjustable bipod and flat L7A2 buttplate


Without further ado, here are my upgrade and modification notes for the Echo 1 M240B:


Gun performance goals

  • Reliability should be the driving force behind any modifications or upgrades you perform.

  • Aside from reliability, there are a few parameters to keep in mind:

    • Ammunition: shoot the heaviest ammo you can afford. Heavy bbs retain their backspin and kinetic energy longer than light bbs. This means that heavy bbs give you more range and have more punch on target.

    • Rate of fire: MMGs aren’t conducive to mobility. As such, you should aim to have a fairly high rate of fire so you can reliably engage targets at distance. Don’t worry about reloading too much, as someone can top up your box mag while you stay on the trigger. 1300 rpm (about 22 rps) is a good goal.

    • Range: over-hop your bbs so they “float” during their trajectory. Don’t over-hop them to the point of losing them within your sight picture, just apply enough overspin to squeeze out that little extra bit of range.


Echo 1 M240B externals

  • Weight

    • Weighs about the same as a loaded-out CA M249, just a lot more awkward to carry

  • Bipod

    • It’s okay. Not as good as the real M240’s bipod, but not nearly as bad as the A&K M249’s bipod

  • Carry handle

    • Pretty damn sturdy, no concerns on my end

  • Barrel locking mechanism

    • Can be a little loose, leading to the barrel detaching if you’re not careful about disengaging the carry handle from the barrel locking collar by pulling the “trigger”

  • Top cover

    • Tends to break near the hinge point if optics are mounted, so be gentle when closing it

    • Be mindful of the wires running under the top cover; it’s easy to accidentally chop them, rendering the gun inoperable

  • Feed tray

    • Needed to hold the feeding adapter in line with the hopup unit

    • Do not discard or replace with a real M240 feed tray; bb feeding issues may result

  • Muzzle thread

    • Female M17-0.75 CW (+) thread; this is threading INSIDE the muzzle of the gun, not outside like most guns

    • Attaching another flashhider will require machine work

    • Real M240 flashhider thread: 25/32-24 UNS-3A CW female thread

  • Stock

    • Hollow plastic; feels kinda cheap, but reduces weight

    • Battery compartment in buttstock

      • Included 9.6V battery is 24 x 48 x 171mm

      • Max LiPO size is 23 x 31 x 170mm (due to square cross-section of LiPO vs rounded opening in stock)

    • Sliding the buttstock on and off to change batteries will eventually lead to breaking off the trigger switch tabs, rendering the gun inoperable

      • I recommend rerouting the battery cable forward so the battery can be stored in the boxmag pouch


Echo 1 M240B internals

  • Inner barrel

    • Stock component

      • Stock length is 550mm, which means it ends just before the front sight

      • A nylon inner barrel stabilizer is included; without it, excessively wide groupings make the gun unusable past 50 feet

    • Upgrade/modification

      • A 590mm inner barrel will fit; it ends just before the open “birdcage” portion of the flashhider

      • 590mm barrel doesn’t yield optimal performance since the compression ratio is already so low; I used a 590mm IB to prevent bbs from striking the inside of the elongated GPMG/MAG58 flashhider

      • Tightbores aren’t necessary

      • That said, I have a Prometheus 6.03mm EG inner barrel in both of my MGs. This is to get a little more juice out of my guns without increasing gearbox stress with a higher rated spring.

  • Hopup unit

    • Stock component

      • Stock unit is decent quality and has okay range of adjustment

      • Takes standard hopup rubbers and nubs

    • Upgrade/modification

      • None needed

  • Hopup rubber and nub

    • Stock component

      • Standard black rubber ACM affair

    • Upgrade/modification

      • I’ve become a big fan of Prometheus purple (soft) hopup rubbers/buckings. They provide consistent backspin, improving groupings at range. They also last a pretty long time, about 50k rounds.

      • I use the stock Promy purple hopup nub. Using an excessively hard nub, like a bic pen ink tube in lieu of a standard rubber nub, is a great way to destroy accuracy and induce jams (this doesn’t apply to stock hopup units with vertical nubs).

      • If you aren’t getting the full range of engagement out of your hopup unit, add a layer of shrink wrap over your existing hopup nub to beef it up a bit.

      • I advise against using flat hops or R-hops in machine guns, since they are more finicky and don’t last as long as standard hopup configurations.

  • Gearbox

    • Same gearbox shell as the Echo 1 M1918 BAR, although the motor cage is different

    • Seems to be the same overall size as the S&T/Lancer Tactical M240 gearbox

    • Not compatible with Golden Eagle/Matrix M240 gearbox; Matrix gearbox has a longer overall length by 1-2mm

  • Air nozzle

    • Stock component

      • Made of machined brass

      • 20.5mm overall length

      • No “step” built into body

    • Upgrade/modification

      • Has an internal o-ring; if it gets worn out, replace with a 5mm ID x 0.8mm C/S o-ring

        • Do not use a 5mm x 1mm C/S o-ring; airseal will be perfect, but feeding will be sporadic due to tight fitment on cylinder head stem

      • Closest aftermarket approximation is SHS P90 air nozzle (at 20.8mm overall length); still not compatible due to smaller chamfer at end

  • Tappet plate

    • Stock component

      • Similar design to V6 tappet plate with “pushing” tappet spring, but with a shorter air nozzle arm for a concentric cylinder head stem

      • Same overall length and height as V3 tappet

    • Upgrade/modification

      • Seemingly compatible with V9 tappet plate and VFC SCAR-H tappet plate, although the latter has not been tested

  • Cylinder head

    • Stock component

      • Stem length: 18.6mm

      • Very similar to V3/AK cylinder head, but “collar” around air nozzle shaft is 2mm taller

      • AOE correction is needed for the cylinder head: either a 3/16in neo pad or a Lonex AOE correction piston head will work

      • The stock cylinder head is fine; no upgrade needed

    • Upgrade/modification

      • Fits V3 cylinder head with raised “collar” segment a la Lonex V3 cylinder head, but modification is required:

        • Remainder of cylinder head “collar” must be built up to be even with the raised segment; I cut up an old Cyma AK cylinder head and JB Welded pieces of it onto the Lonex cylinder head

        • This modification is to ensure even shock/stress distribution across the cylinder head collar

      • Stock cylinder head will not work with V9 tappet plate due to tight fitment

  • Cylinder

    • If yours doesn’t have a full cylinder, which it should, buy one

  • Piston/piston head assembly

    • Stock component

      • AEG standard components, nothing fancy

    • Upgrade/modification

      • Increasing piston+piston head mass induces minor joule creep

      • Using a Lonex red high-torque piston coupled with a Lonex AOE correction piston head yields a 10 fps boost with 0.3s versus the stock configuration

      • Lonex hollow o-rings give a better, longer-lasting seal than standard o-rings. I use them in everything.

  • Spring

    • Stock component

      • Standard AEG spring, comes with two springs if bought new: one for 400 fps and one for 450 fps

    • Upgrade/modification

      • Guarder SP130 yields about 1.6J with all other parts being stock

  • Spring guide

    • Stock component

      • Stock spring guide is an unsecured/”floating” design, which is awful

        • Simple spring guide rests on top of washers and a bearing set, which sits in the QD spring plug

        • If the spring breaks, the spring guide, bearings, and washers will be let loose into the gearbox

    • Upgrade/modification

      • A V2 ball bearing spring guide can be ground to fit into the QD spring plug without much effort; it can then be secured with a M5-20mm bolt (with the head ground down to ensure clearance of the QD spring plug pin)

  • Gears

    • Stock component

      • Stock gears are decent quality, no need to replace

    • Upgrade/modification

      • If one of the gears does strip, skip the and install a set of Siegetek single sector gear (SSG) standard ratio (20.8:1) gears. If properly shimmed, they will last forever.

      • Big *fruitcage* off steel shims are great for maintaining gear stability. Prometheus makes a 24-piece set that fits the bill perfectly.

  • Bearings

    • Stock component

      • 8mm bearings as standard

      • Decent quality, but I have had one seize on me. This failure destroyed my sector gear

    • Upgrade/modification

      • I’d recommend replacing the bearings with Lonex 8mm steel bushings eventually

  • Antireversal latch

    • Desperately in need of shimming

    • Without proper shimming, the ARL spring tends to break, leading to one of two things:

      • ARL function ceases, leading to the first round of every burst being a double feed

      • ARL incorrectly engages, jamming the gearbox

  • Motor

    • Stock component

      • Stock motor is a high-torque short type with a ventilated can

    • Upgrade/modification

      • Some motors (stock, SHS, ZCI) fit slightly loose in the motor cage

        • This leads to the motor twisting within the motor cage when firing

        • Over time, the motor cage may break from this torqueing

        • Wrap the motor housing with 1-2 layers of electrical tape to ensure a snug fit and reduce/eliminate motor twist

      • Motor height is touchy

        • Many pinion gears will extend too far into the gearbox, even with the motor height fully backed off; this leads to the pinion or bevel gear stripping

        • Slide the pinion gear further down the motor shaft to avoid this issue, if possible

  • ASG motors are too long and don’t fit properly in the motor cage

  • Trigger switch

    • Similar to the M249 microswitch, but without the metal lever

    • Use a MOSFET to prevent the trigger switch from burning out


    • Stock component

      • Stock unit is a dual signal wire MOSFET with contacts branching off main power output to feed the boxmag wire

      • Built-in mini blade fuse holder

      • Symptom of failure: dead trigger or runaway gun

    • Upgrade/modification

      • Gate WARFET is a great replacement

        • You’ll need the programming card to get your WARFET set up properly

        • New wiring harness should incorporate the included dual signal wire setup

        • To power the boxmag, don’t try to make a parallel/Y-harness; they break constantly no matter how well you solder them. Instead, buy a parallel Deans adapter and run two separate plugs: one for gearbox power, one for boxmag power.

      • Gate NanoASR isn’t rated to handle the electrical demands of the gun

      • I recommend re-routing the battery connector forward and under the feed tray so the battery can be stored in the boxmag pouch

  • Fuses

    • Stock component

      • ATM type mini blade fuse

    • Upgrade/modification

      • You should really have an analog fuse, even if your MOSFET has a digital fuse built in.

      • I use mini blade fuses (ATM type) in an automotive fuse holder, soldered into my gun’s wiring harness between the battery and MOSFET

  • Batteries

    • LiPOs are fine for MG use, so long as you don’t drain them completely

    • I’m a fan of 11.1V since their performance suffers less in cold weather

    • Make sure your normal/peak discharge rates are, at minimum, 20C/40C. Otherwise you’ll over-tax and *fruitcage* up your battery.

  • Battery connections

    • Stock component

      • Large tamiya connector

    • Upgrade/modification

      • Deans are the way to go

      • Tamiya connectors are rated to 15A; Deans are good for up to 60A

      • Avoid melting your connections, go Deans


Echo 1 M240B box mag

  • Biggest failure point on the gun

  • Powered by gun’s main battery

  • Servo drives a pulley, which is connected to another pulley via a drive belt; this second pulley drives the feeding mechanism

  • Servo characteristics

    • Micro size RC servo (28.6 x 28.6 x 12.7mm)

    • Operation: continuous rotation

    • Motor: 2 pole, with a resistor run between the motor connectors

    • Gears: metal

    • Servo has single mounting holes on each wing

    • Servo has interchangeable heads (via a phillips screw)

    • Servo is run on main battery power; the resistor located on the motor (likely) serves as voltage regulation

  • I rewired my servo with the same 16 AWG wire I used for the gun’s wiring harness

    • Disassembled the servo housing

    • Pulled out the servo motor

    • Desoldered the existing ~22 AWG wire

    • Soldered on about 22in of the 16 AWG wire

    • The higher gauge wire increases the boxmag’s feed rate, which is great if you install an upgraded motor in the gearbox

  • The drive belt tends to get worn out and loose, leading to feeding problems; replace with a piston head o-ring as needed

    • Lonex hollow piston head o-rings seem to provide more grip, leading to less slippage on the pulleys and more consistent feeding

  • Also check pulley mounting bolts for tightness; loose bolts will lead to feeding problems

  • Sometimes, the feed tube will become detached from its mounting collar, spilling bbs at the point of disconnect

    • Connection points are at the feed adapter/mounting plate (attached to the gun) and inside the box mag, under the feed mechanism

    • Wrap the end of the feed tube in electrical tape and secure it to the connection point to prevent this issue

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Nice review: 

In relation to the Inokatsu:

There were 2 versions, Alu and Steel.  I have the Alu version and wished I had the Steel one, but literally it was the last one for sale I bought it from Hawaii and shipped it to HK where it was then broken into pieces and smuggled into NZ.

It clocks in at 8kg unloaded and around 10kg with box mag and rounds.

Mine has been a loan "torture" gun for noobs , permanently set at 500fps to teach  airsofters appropriate machine gun use.  It is quite funny to watch players struggle carry the thing up a 2km hill.

No issues after hundreds of thousands of rounds.  I have had to change the piston once.  

Compared with my A&K M60/M249/PKM and G&P M249s, the real strength of the inokatsu is the heavy duty motor and magazine, where debris can get into the mechanism and rounds would still come out.  Whereas the M60s or M249s small amount of sand or foliage and would jam the feed mechanism.

The weakest part is also the magazine housing, which is cardboard.  I constructed a folded polycarb box for field use and over 8 years it has slowly disintegrated.  Now I retrofitted an A&K M60 box mag shell so that will last a lot longer.

Only thing that really affected this was the  hop chamber and air nozzle fitment.  Hop chamber is too wide, and the air nozzle it came with was too narrow, which means that the air nozzle would wobble and as soon as the autowinding mag was in tension it would push the nozzle out of airseal alignment with the hop rubber.  To fix it I created a thing sleeve that holds the nozzle in place.

Other than that its a workhorse.

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Really good points on the Inokatsu. I never figured out how to get mine running reliably, so I sold it off at a huge loss. A shame, since it was an absolutely gorgeous gun.


Funnily enough, a good friend of mine acquired it after several re-sales. Do you have any tips I could give him in order to get it running again? Currently, the gearbox "recoils" in the receiver, pulling the nozzle out of battery during firing and making airseal very inconsistent.

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I need to see your mechbox "recoiling". 


Mine, the mechbox is held forward by the faux buffer mechanism which is in the stock and pushes the mechbox foward.  There is no "recoil", even with its crazy 500fps spring.


Perhaps your recoiling is the same issue I had with the air nozzle and hop unit?  



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The faux buffer is weak enough to allow the gearbox approximately 5-8mm of movement in the rearward direction when firing. The movement of the piston is enough to get the gearbox sliding back and forth within the receiver.

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I imagine so. I’ll talk to my buddy and see if he’s willing to tear the stock down and try to toughen it up.


Pity the gearbox isn’t supposed to do that. The “recoil” effect was very satisfying, as only a 3lb moving weight can be.

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