Magwells Classic Army MK46 / M249 Guide

[Magwell]

Another update, and more box mag fun...

As I might have indicated earlier in this thread, I also have an A&K MK43 Mod 0 (M60-E4), and despite some serious reliability issues that had to be overcome which involved a complete teardown and rebuild among other things... That MG was a beast, or Pig perhaps . One of the things that made it so effective in some of the situations I'm thinking back to was the massive box mag, at around 4500 rounds if I remember right. The larger capacity of the M60 and some Russian variants of MGs allow those weapons platforms to dominate positions with volume of fire. I know I've mentioned before that this MK46/M249 build is aimed at light weight and mobility, but I would like the option to pack more ammo for some milsims. Here, our rules for sims are that MGs can pack one full box mag, and does not differentiate on capacity. So I can either rock the 1500 round 'nutsack' box or 2400 round standard box. While the 1500 is fantastic for assaulting and mobility, I've always felt the 2400 round box was a tad wasted with only about 40% of the box actually contributing to ammo capacity and having 60% lost to internals when the nutsack mags can pack over half that for considerably less size.

I've been contemplating this since first disassembling the 2400 round box mag, and I finally pulled the trigger on my 'franken-mag' which holds an estimated 5500 rounds hahaha. My intention is to use this for milsims with more open area, less trees, and plenty of structures. The field I have in mind is entirely open area and structures. On many occasions I've bled the 2400 round box dry and been left with my pistol or running back to respawn to reload.

At any rate, I made this using 1x A&K 2400 round box and 1x A&K 1500 round box. The construction is fairly simple and involves splicing the internals of the 1500 round box into the 2400 round box shell, splicing the feeding tubes together, and rewiring...

So here's the comparison of the two boxes, brand new:



And here's a couple shots of the internals. Virtually the same parts in difference configurations.






After test fitting I used my dremel to remove some plastic that was in the way, although it fit extremely well right from the get go.



To fill the void left by the smaller width, I cut some foam and hot-glued it to the internal mechanism to keep bbs out and keep them rolling to the mechanism. It's hard to see in the picture but the top is tapered.

Since the spring feed tube on the 1500 round box mag isn't long enough to make it to the magazine insert without stretching horribly, I cut the spring and used some extra plastic tubing I had laying around to connect cut spring and the left over spring from the 2400 round box. After bridging them (already snug) I used a heat gun to warm up the tube and then clamped down on it to get the semi-melted plastic to mould to the spring so it could not slip out.



And then a test fill. I had estimated it would hold around 5000, but after filling it completely with a brand new bottle I'm estimating around 5500 now.



After that I disassembled again and re-wired it. To secure it in place I used four of the screws securing the fabric on the 1500 round box to the plastic and screwing the top and bottom pieces together. I used a 1/8" drill bit to pre-drill the holes then fired in the hex head screws. Lastly it saw some paint to match the camo scheme and was tested. I'm quite happy with this project and if you need some more firepower it's relatively easy enough to do with some patience and know-how, although it is quite expensive for what you get considering you have to buy two box mages and then combine them into only one.

[RainyEyes]

Can you take a picture of the sound card motherboard in the mag box? I cannot for the life of me find one and I need to reaolder it.

[Magwell]

Originally Posted by RainyEyes

Can you take a picture of the sound card motherboard in the mag box? I cannot for the life of me find one and I need to reaolder it.

You bet. 1500 round 1st, then 2400 round box for the 2nd and 3rd pic. The cut yellow and black wires in the 2nd and 3rd pic went to the motor.

[Airoz]

updates on this?

[Magwell]

Originally Posted by Airoz

updates on this?

Hey - updates on which part specifically?

[Magwell]

A few updates...

Had our first warm game in May (lots of April snow on the first game) and the MK46 performed beautifully, despite running down all my batteries. So in early June we had a tech day and I tore open the gearbox. Everything seemed fine until I was reassembling it and re-checking shimming, I noticed the gears would move normally and then bind to the point where I could not turn them by hand. So after fixing this and relubing everything, the MG was back up for the rest of the summer!



In late June at a skirmish game I ran into an odd issue that took a while to chase down... With my A&K 1500 Rd nutsack mag I would experience a jamming issue that sounded like double feeding. Sure enough a BB would roll down the barrel and the gun sounded like it was jammed. Despite clearing the barrel and reassembling multiple times, the issue persisted. My initial thought was, naturally, hop up and bucking. The bucking has seen significant use, and probably time to change out. It was... You can see the indent from the flat hop nub here.



And the wear on the inside. Note that most of this is where the bucking was modified to be a flat hop, the contact area is the dark portion near the top. Time to change regardless.



And, a new bucking installed!



After further testing, standard M4 mags and the 2400rd large boxmags fed and cycled just fine, which led down a long road of trying to solve a feeding issue with the box mag.

As it would happen, yesterday we had another tech day where I fully disassembled the nutsack mag, tested various fixes (which worked to varying degrees, but none solved the problem entirely). After a long period of trial and error I removed the gearbox to have a look inside, because hey, it couldn't hurt right.... oh boy.

So what presented symptoms as a jam turned out to be a partially stripped motor pinion gear and heavily worn piston rail. I didn't snap pictures of the rail but have a look at the motor. Granted, this is after thousands and thousands of rounds, so no surprise there just a reminder to check everything when diagnosing problems.

So, took an old spare I had initially purchased for my M60, along with a new piston rail, relubed everything, reshimed the bevel gear to the spur to get it running again, and ordered an SHS high torque motor. I also replaced the trigger switch because it was original and during the last time I used it, something caused the gun to run away on full auto. It was a rainy day so it might have just been the signal wires in the mosfet getting a little moisture in there, or it could have been wear on the trigger switch. Either way, cheap part and cheap insurance.

Here is the motor, the next picture is the tooth it lost.





And here is a video from my buddies GoPro strapped to my helmet during a few skrims, shows the MK46 in action. https://youtu.be/0F4k6Op6rjo?t=89

[Magwell]

Two updates in a little over a week!

Another big one... Had a big game this past weekend (what a blast) so last week I broke out the MG to do some final checks/testing. During the testing, I noticed my FPS was consistently low, so I pulled the stock off and checked the spring. Sure enough that was the issue, it had broken haha. I guess you put enough cycles into it and it will snap.



Looking at an early 4am morning drop off at the airport the following morning, I packed up after this discovery and called it a night.

Friday before the game I broke out my tools again to finish the work I had started. I also received a package of joy from Canada Post, brand new SHS High Torque motor!



So after making the necessary adjustments for motor height I went and put it all back together, found an appropriate spring in my collection of spares and went to test fire. Initially things looked good, she was shooting around 340 FPS with 0.28g bbs, which is the equivalent of a hair over 400 FPS with 0.20g. Wanting to check my 1500 round box mag I did some more shooting only to see the FPS consistently drop to 240ish and fluctuate significantly.

So cracked open the gearbox again, tested airseal at the piston/cylinder - ok all good there, tested the nozzle and found that the O Ring on my SHS nozzle was more or less garbage after seeing a ton of use. Not surprising. I had recently run into a similar issue on my ICS M4 that I put the same nozzle in a year or so earlier than when I did the MK46. On my M4 I also found that with a prommy purple bucking, the SHS Red M4 nozzle is longer than I like (21.4mm) but the AK Long nozzle (20.7mm) seals up fairly optimally. I happened to have a spare so grabbed that, tossed it in, and she was back up shooting 345-348 w/ 0.28g bbs consistently!

Worth noting is that this setup is very specific to the parts I'm using, nozzle length should suit your combination of airseal/hopup parts.

Lastly I took the Gate MERF 3.2 mosfet I had been using in my M60 and transferred it over to my MK46. With the trigger being able to give a single shot with a rapid trigger pull, I decided to maximize that with the mosfet setting the "fire control" to a 3x burst on "semi" and full auto on full auto. So with a rapid trigger pull, the MG now fires a 3 round burst, and holding the trigger longer gives normal full auto functionality. This turned out to be super useful for closer kills where I wanted to make sure I hit my target, but not overshoot someone. This turned out to work very well for close range ambushes on multiple targets... 3x burst - next target, 3x burst - next target, etc.









So, after that it was off to finish packing for an early start and then heading out to OP Valour 2019. Game had a great turnout with 260+ in attendance raising around $17,000 to support PTSD.

A few shots from the game, MK46 in action along with some mounted LMG eye candy!


Escorting an armoured column up a narrow road, we expected an ambush and were not disappointed! The MK46 and a team mates Stoner LMG were instrumental in allowing our riflemen to move in and eliminate OpFor attempting to disable the column.



Our squad advancing on an enemy position defending a hidden WMD.



Getting ready to advance on the enemy position. We unfortunately got outflanked while attempting to flank the enemy position, our squad of 3 got hit by a large force from behind in poor terrain.



Humvee complete with mounted M60


Hagg 5 complete with M134 minigun, knocked out.

[Magwell]

New year... New parts!

I decided to change up a couple things on my MK46... the madbull barrel has had some light scratches on the inside since day one (arrived this way) and with a boxing week sale at Redwolf Airsoft on Prometheus Barrels, I couldn't say no. I also picked up some replacement body pins to replace the retaining nut that I lost at OP Valour 2019. Lastly I snatched up an A&K Polymer buttstock. I do like the setup shown earlier in this thread, but its just time to try something new and change up the look of the gun.

For the barrel, I dropped in a 380mm 6.03mm barrel, nearly maxing out the length an inner will fit in the outer and flash hider. FPS did jump a bit, but I was testing with no hop before/after. With hop applied the FPS jump should be minimized.



And on to the stock.. some modification is needed! The butt plate is quite different than the stock MK46 one, and the rear shoulder rest does not 'latch' in the down position and rattles around a bit. In terms of geometry, the top of the stock lines up pretty close to where the buffer tube mounted stock sat but the length is roughly the same as the 'position 3' spot on the buffer tube. When fully compressed the original setup is roughly 2" less than the poly stock.

First impressions are great. The metal on the stock is magnetic but it is soft and quite easy to file through (see below) suggesting iron or low carbon steel. The plastic looks to be a high grade polymer similar to real steel stocks. My only complaints in the construction are the sheer over design of the butt plate and that the stock is a touch loose where it meets the butt plate. After applying some masking tape to the rim where they meet this was completely eliminated though and the stock is rock solid.











So after a few hours of modification, the butt plate is a little closer to the factory one. This is important for a couple of reasons...

1. The plate does not fit properly because it is too wide, rubs quite badly trying to get it to close, will not seat with the bottom pin in and 'hinging' the plate upwards, and the rear pin does not close properly with the extra width.
2. The wires get pinched in a rear wire application, and the butt plate actually gets hung up and won't close






After testing out the rear sling mount (and not liking it) I decided to do a custom sling mount at the rear of the butt plate, similar to the buffer tube butt plate mount. I started by marking and drilling one hole in the top of the poly stock directly behind where the butt plate stops, and drilling a second one through the butt plate itself. this allows some paracord to be looped through and around the metal butt plate and then a loop pulled through the stock for the sling to mount to.







After test fitting, the plate would not close and I discovered that the paracord was pinched on the back of the gearbox. So, out come the files and sandpaper again to create a channel for the paracord to sit.





With the butt plate sorted out, it was time to look at the poly stock and rear plate. I love how much space there is in this thing, but its almost too much. The last thing anyone wants is a battery bouncing around inside the stock. So once again I grabbed some leftover foam from a Gate mosfet box, broke out the hot glue gun and secured some 1/2" foam to one side of the stock. I also tried a few things to get the rear shoulder rest to secure nicely and settled on heat shrink. The wire shoulder rest can be pulled apart by hand, and then slipped out from the holes in the stock to remove it. Three loops of gradually larger heat shrink added enough girth to allow the shoulder rest to actually 'click' into place. It's a nice satisfying sound and it will not budge until needed.



And finally the wiring needed some updating as well. With the mosfet buried deep inside the stock, a simple wire extension is used to allow a battery to be connected and then tucked into the stock.





And lastly a shot of the freshly painted stock mounted on the gun.



All in all, I like it so far. At first it's a little awkward after being so used to the previous stock, but muscle memory just needs to be updated. I found the low ready to be a little better with the length of the stock over the high ready. The corners on the 'stops' for the shoulder rest are quite sharp when they dig into your arm while lifting the butt of the gun up quickly. Some wear or filing would take care of that, but for me the issue is my arm length - my left arm needs to extend fully to get enough clearance at my shoulder. With body armour on, this will probably snag so I'll likely stick with the low ready for the most part.

[Magwell]

With the Covid-19 situation resulting in a lot of extra free time, I decided to fully rebuild my MK46 gearbox and do some more work on the externals... Figured if I get that effective range up I can social distance while putting rounds down range... right

So first I reshimmed the gearbox and swapped out my piston for an SHS lightweight one along with running final checks on my cylinder volume vs barrel volume. Credit here for a great guide on volume matching: Link. So after building an excel chart for future use and plugging in the numbers off my build, a 380mm barrel is perfectly matched with a hair of overvoluming on the cylinder.



After that, going through and checking AOE on the piston I noticed some strange contact points. Turns out the SHS piston with its larger pickup tooth actually contacts the portion of the sector gear that meshes with the spur gear. So out comes the dremel to trim that down a bit, after which the piston was still binding slightly. So after some further investigation the contact point is the pickup tooth again meshing with the leading tooth of the sector gear. So after trimming that down a bit, the piston and gears mesh beautifully and the gearbox is running superbly. ROF, unsurprisingly, increased as well.




After getting the gearbox all sorted I turned my attention to the stock buttplate again. It was meshing well, but tight in a couple spots. So dremeled off the one edge completely to free up some more room for wiring, after this no more pinching! Lastly, the plate didn't like to line up with the upper body pin holes. It would work, but wasn't properly aligned and somewhere, something was getting twisted to make them align once the pin was tightened. Using the dremel I enlarged the lower body pin hole on the butt plate and after taking off a small amount of material, everything lined up nicely like the stock CA one did.



After that while reassembling everything I noticed some resistance on the barrel retention clip. After taking a closer look something was certainly off, it has significant resistance towards the ends of the arm travel and the wheel that secures the barrel in place was jammed, with obvious signs of wear from where it meets the barrel - evidence this was a long term issue. The body pin holding the arm in was wedged and had to be pried out (can't get a punch on the opposite side). After taking a look at how everything tied together, this arm was either damaged at some point (took a spill while running up a hill summer 2019, might have done it) or it was always this way and only now had dug into the body enough to catch. I did try bending the 'tabs' to be aligned but this proved useless, further suggesting it was this way from the factory. Either way the angle of the pin was about 95 degrees and this was forcing one side to grind against the gun body. By dremeling out a little bit of material from one side the pin was able to align and now it holds the barrel in very securely with no resistance on arm travel. The first picture below shows the wear on the gun body from where the catch was contacting it.

[ThunderCactus]

ugh. guns. am i right?
If it's any consolation, my snow wolf M24 is everything you'd expect from a $180 gun pretending to be a sniper rifle. Lots of shimming and retapping holes.

[Magwell]

Originally Posted by ThunderCactus

ugh. guns. am i right?
If it's any consolation, my snow wolf M24 is everything you'd expect from a $180 gun pretending to be a sniper rifle. Lots of shimming and retapping holes.

Lol just saw this today! Yep... but hey thats all part of the fun right! Tinkering with it and those little modifications to make it "yours"!

[Magwell]

Ok folks... long/big update today.

A lot of this was completed before the dreaded C21 announcement killed some of the teching motivation, but trying to be optimistic. At any rate, got a lot of work done on this bad boy over the winter.


For starters, I'm 6'-0" tall but my legs are a little disproportionate as with many of us. Compared to an "average" human proportion my legs are a little longer and my torso/arms are a little shorter. As a result, and because fixed stocks on body armour really push any platform far forward I wanted to reduce the length of my M249 fixed stock. So I did what any normal/sane person would do and took a hacksaw to it... Seriously though I did a bunch of pre-planning, measured out 38mm (1.5") and predetermined where the new pin holes would end up and how much material I would need to remove from the butt plate, then went to town. It was pretty meticulous work planning it out, and a lot of dremeling but I'm happy with the results, really helps with transitions and supporting the weight of the LMG. More pictures later of the finished result.





Next I decided to remove anything that wasn't providing a purpose on the gun. The real MK46 for example removes the front mounting lug, so I chopped all 70 grams (yes I weighed it) off using my dremel and a cutting disk then cleaned it up with a file.



Next I turned my attention to the far front end, where one gram really gets heavy due to it being on the end of the gun, and there are a couple considerations. One is the barrel locking mechanism... or what at least tries to. The barrel sleeves into the fake gas return at the front, locks in at the rear, and is stabilized by a "U" shaped piece at the front. Not sure about you guys, but mine doesn't really do much for stabilizing it and allows what I'll guess to be 10 degrees play from left to right. So to combat this, I made a larger U shaped piece out of flat 1/8" thick aluminum plate, cut off a chunk of metal from the fake gas return that was serving zero purpose (34g) then drilled and tapped new screw holes to secure my new plate in place. I also threw some nuts on the end as I over-sized the initial holes so there wasn't as much thread as I had planned and one of the holes striped a bit. Some new paint and it blends right in, and it really locks the barrel in place, zero movement now with just enough gap for it to smoothly slide in/out. If I remember right, the barrel OD is 22mm.







Next, it was on to something I'm really proud of. I've never been a fan of the lower tri-rail on the MK46. It's bulky and not a great hand-hold even with a grip, the CA one at least has a poorly engineered attachment system of two Z brackets that are a soft metal and need to be bent back into the proper shape every now and then to keep the rail tight, and for me at least, I only use the lower rail.

So... why not fabricate one from scratch.

I went out to the Metal Supermarket (for real, it's a thing https://www.metalsupermarkets.com/) and picked up some 6061T6 hardened aluminum square tube, 1.5" square x 0.12" sidewall x 5.75" long. Then I cut it down to about 1.25" tall to get a U profile, sanded down the cut ends with 100 grit sandpaper to get rid of the burrs and rough spots, then started the slow process of removing sidewall thickness on the vertical sidewalls to get it to properly fit over the MK46 body. Not much was needed, but the material is pretty tough to sand down using a dremel.







Next I marked and drilled 4 holes to align with 4 pre-existing tapped holes on the MK46 body, countersunk the holes in the new handguard and secured it in place with four tapered machine screws.





Then the fun really started... I drilled and tapped four holes to secure a 2" rail segment in a couple different locations, or a 4" rail segment, to keep my options open. After that I took care of some weight reduction by swiss-cheesing the sides, followed by a coat of tan 'primer' as the base coat for my camo. I was really thrilled with how this turned out, but I didn't want to put the traditional heat cover back on, and wasn't a fan of the open top style of M249. So I dug around to see what I had that might work, found some brand new/never used rail covers that came with a gun I got at some point... busted out the drill and tap again and secured the rail cover to the barrel with 3 M4 machine screws to create my own style of heat shield. The great thing about this is it keeps the front end light weight and slim, to the point where I can get a C-clamp style hand grip if I choose to, although I have large hands.









With the above adjustments, I tossed it on the scale and was happy to see it pop in at 5.173 kg / 11.4 lbs. The 1500 round box mag and dummy rounds (fully loaded) came in at another 0.933 kg / 2.06 lbs. Combined 6.106 kg / 13.46 lbs and with nearly all that weight savings off the front end makes this LMG feel like a completely different gun.



Thats it for tonight, but I have a few more things to add soon with some unique tweaks to the 1500 round A&K 'nutsack' box mag and some hop up upgrades

Stay safe and keep OpFor suppressed!

[Magwell]

Long time no post...

MG is still going strong, life has just been different with less time to post. Some of this I did a while ago, but it's worth sharing.

I never did like how when you have a box mag feed system installed, the tab on the magwell slot for the stanag mags pushes the dummy bullet belt up, it looks odd in my opinion, so I wanted to change that. As such, I cut most of the tab off so it no longer sits in the way. There is enough left to still use it as a mag release, but the effect is much cleaner.

I also modified my box mags so that the bullet belt can 'slip' on/off a dummy 5.56 round. These have holes drilled and tapped into them, then bolted into the box mag. On my nutsack mag, I relocated the motor wire and connector so it comes straight up out of the box instead of being fed through a spring wire shroud on the left. This cleans up things quite a bit and I may do this to my larger 200rd boxes as well. This involved a bit of filling/sanding/painting. Lastly, painted the tips of the dummy rounds green to replicate M855 ball ammo, although after a couple years it needs to be repainted as its mostly been worn off. The bb feed tube was also relocated to sit below the fake bullet belt for better aesthetics and reliability, and the cheap factory screws that hold the top to the bottom of the box and clamp the fabric in place were replaced with M5 screws/nuts with the nuts JB welded to the inside of the box mag. Similar modifications were made to the bottom of the mag, with the factory screws replaced with M2 screws and M2 threaded inserts as the factory screws had stripped the plastic after only a few times being removed/reinstalled.













Later in 2021, I R hopped the barrel using an Elvish Tac pre-cut patch and spacer. Works great and I'm very happy with the results.







Otherwise it's been mostly maintenance and wear replacement. Had one SHS motor die after years of use, one spring break due to high cycles. Box mag motors on two boxes died in 2023, and I can confirm that the Tamyia Atomic or Torque motors are basically a drop in replacement, while being what looks like much higher quality. The pinion gears they stock as well are a direct replacement as I ended up enlarging the bore of the pinion on my nutsack mag after years of use and presumably friction. These replacement motors have an RPM in the 12,000 - 15,000 range. If you want a higher or lower RPM to suit your specific build the Tamiya racing motors line has a wide range of RPM, and you can find that info online. Keep in mind that there is some gear reduction within the box mag, but I cannot speak to the ratios as I have not looked into it. I'll report back after some testing, but I expect each of these motors (I used one of each) will exceed my ROF of 19-20 RPS.

Motors:
https://www.tamiyausa.com/shop/racin...tuned-2-motor/
https://www.tamiyausa.com/shop/racin...-2-motor/none/

Pinion gears:
https://www.tamiyausa.com/shop/perfo...forced-pinion/
https://japan-figure.com/en-ca/produ...RoCLSgQAvD_BwE

[Magwell]

This weekend after some further digging into circuits and motors, I wanted to see if anything in the wiring of the box mag was causing the motors commutators to burn up, which is how all the motors had failed.

After some reading I discovered that the 8.4v going to a ~3v motor is not great for the commutators, which will likely lead to sparking and overheating/melting of the commutators. So I set out to learn how to resolve this, and a few articles and handy online calculators later I have some resistors in the mail to modify the wiring per the below diagram I put together. Will post again once rewired to show how that looks and results. All the calculations were done using a fully charged 7.4v lipo (8.4 volts), a maximum motor draw of 2.2 amps at motor start up, and a motor input voltage of 2.4-3.0 volts. In other words its designed using the highest load, even though the motor amp draw will likely drop once the motor is turning.

The following handy Voltage Divider calculator from Digikey was used to determine the resistor values, and can be adjusted with an input voltage of 12.6v for an 11.1v lipo at full charge.
https://www.digikey.ca/en/resources/...oltage-divider

The following Voltage Drop calculator was used to determine wattage rating for the resistors and will need to be used as well for an 11.1v lipo. The motors I'm using have a max draw of 2.2 amps for reference.
https://elecurls.tripod.com/drop-res.htm

In the below diagram, the following resistors are used:
https://www.digikey.ca/en/products/d...-5R60J/2564360
https://www.digikey.ca/en/products/d...-10R0F/2360935