Magwells Classic Army MK46 / M249 Guide

[Magwell]

Another update, small one...

I've decided to difinitively reduce my ROF, 22.5 RPS is too high for my liking, and this recent jump to 24.5 with the small box mag is way too high.

So after doing some research, in very loose terms...

Input Voltage will dictate a DC motors speed
Input Current will impact the available torque a DC motor can put out

To relate this back to the batteries, the voltage (ie 9.6v, 9.9v, 11.1v, etc.) needs to be reduced from 9.9v to reduce my ROF, without cutting the amperage supply of the battery too much.

I have a package of resistors kicking around, so attempted to resolve this by creating resistance across the motor input, but even at 1 Ohm, it was too much. So after some testing with other batteries, I can achieve 18-19 RPS with a 7.4v Lipo. Sourced some 2200 Mah 7.4v batteries with near identical dimensions to the 9.9v LiFe batteries I'm using currently and this should put the ROF concern to bed. More on that once they arrive!

[ThunderCactus]

The G&P 249 also uses standard V2 contacts instead of a microswitch, allowing it to use any AB FET out there.
The box mags are designed to hold large batteries in them (great for the PARA model).
There's no mechanical safety, and so the safety is to unplug the battery between the box mag and gun, making it actually MUCH safer than the CA style which can actually short and start firing at random (Rare, but seen it happen myself twice).
It has a reinforced carry handle base, so it won't snap off.
Has a centerline feed system instead of feeding through the magwell, this makes it a bit more reliable.
The V2 mechbox in it is not particularly prone to cracking at all. With the simple addition of a sorbo pad, two G&P 249s I've built have done over 200k rounds each at 400fps and 25rps without cracking. The sorbo's even make the weakest of weak shells, the marui shells, withstand up to 470fps when they'd normally crack at 350fps.
Something I didn't even realize was an advantage until upgrading an A&K, the front sight post doesn't wobble AT ALL, so your barrel remains as rigidly centerline as it does in any other AEG.

Downside is it uses thinner bearings on the bevel gear in order to fit the lower, and at least in the older models, the rail on the handguard was mounted at an angle.


As far as efficiency (this can be achieved on any LMG) I was running 26:1 triple torque gears on an EF1300 motor with 11.1 lipo. Low torque, high speed. 25rps and 350fps, at best got about 9BBs/mah. That's about 350mah for a 3000 round box mag. Closer to 7BB/mah at 400fps.
Full auto is more energy efficient than semi auto to start with, but running low torque on a set of very heavy gears (prometheus) keeps the momentum up with minimal energy. And because the motor has so little torque, active braking barely has any negative effect at all. I ran about 120k rounds through the EF1300 motor before the comm was too dirty to conduct any more. Cleaned it off and it kept on going.

And because of the ability to use any FET on the G&P, you can sue a chimera FET that has motor speed control. So if you want it to shoot slower than 25rps, you can just lower the motor speed in increments of 10%

And the weight on the G&P is actually closer to 7.5 to 7.8kg. The weight difference between them and the CA is significant. I can handle the CA249 like a rifle, can't do it with the G&P lol

[ThunderCactus]

Also, do not wire the box mag motor in series, it will ruin everything.
In parallel, say the AEG motor draws 16A and the boxmag motor draws 4A. In series, there will be 16A attempting to go through the boxmag motor and every other piece of electronics you have in between the AEG motor and the battery.
Parallel is the only way to go.

If you want to be at 20rps, just use a 7.4 lipo, 18:1 gears, and a tienly 35k rpm motor.
35k rpm on 11.1 lipo, 2/3 motor speed is 23k rpm, divide by gear ratio (18:1) = 1280/60= 21rps
This is assuming the load is optimal for the motor, but at 400fps and on 18:1 for a fairly high torque motor, you should be well within the optimal load.

alternatively, using the formula and my build above, just use a low torque high speed (40k rpm) ferrite magnet motor on double torque 23:1 gears (instead of 26:1 gears) and that should put you right at 1200rpm while efficiently sipping amps.

If your RoF is dropping due to the presence of another motor, it's either a resistance or supply issue. So run a battery that can do at least 30A continuous, but also wire the box mag motor directly to the battery, or subsequently use 14ga wire up to the connection point of the wiring for that motor. Think of it like a road, you've got 3 lanes of traffic one way, then you're taking one lane off to go somewhere else while there's still 2.5 lanes worth of traffic trying to go straight.

[Magwell]

Originally Posted by ThunderCactus

Parallel is the only way to go.

Thanks for the contribution, some great info there!

I'm running 14:1 Siegtek gears, 16 GA silver wire with a fet, and the stock motor (so no idea on the rated RPM). Agreed, everything needs to be in parallel, the other aspect to that is if wired in series it negates the ability to use STANAGs.

[Magwell]

Another update... I forgot to consider the bump in amperage due to Mah, so the batteries I initially ordered threw my RoF back to a whopping 24 RPS lol.

Using some logic and the equation for Watts (power), I found a suitable battery. W = I x V where I is the current in amps and V is the voltage.

The 1200 MaH 7.4v 25C/50C lipos had a total power of 444 watts (using the 50C burst rating as I won't be shooting 10s+ continually) which gave me around 18.5 RPS. In order to get 19, I needed a little more power so I ended up finding the 25C/35C 1800 MaH lipos which had a total power of 466 watts, giving me right around 19.3 RPS.

If you're in the same boat, use the above formula if you have a target RPM achieved with a known battery and you want to use a new battery to adjust the RPS.

[ThunderCactus]

The difference is in the internal resistance of the pack, not the max rated amperage of the pack.

In theory, a 25C pack should perform exactly the same as a 300C pack, provided they both provide the (for example) 16A continuous draw that the motor needs.
In practice, higher C packs just have less internal resistance, resulting in a bit more speed.

But the difference between an 11.1v 20C 1200mah and 11.1v 20C 4900mah is (in practice) absolutely nothing.
But you'll gain about 100rpm between a 15C 1200mah and 45C 1200mah.
Your motor draws 16A whether the battery is capable of supplying 20A or 200A.

[Magwell]

Originally Posted by ThunderCactus

The difference is in the internal resistance of the pack, not the max rated amperage of the pack.

In theory, a 25C pack should perform exactly the same as a 300C pack, provided they both provide the (for example) 16A continuous draw that the motor needs.
In practice, higher C packs just have less internal resistance, resulting in a bit more speed.

But the difference between an 11.1v 20C 1200mah and 11.1v 20C 4900mah is (in practice) absolutely nothing.
But you'll gain about 100rpm between a 15C 1200mah and 45C 1200mah.
Your motor draws 16A whether the battery is capable of supplying 20A or 200A.

Yes, but if your battery pack does not max out the motor, voltage being constant, amperage will be the controlling factor for RMP, no?

[ThunderCactus]

If your battery isn't supplying enough amperage for the motor, then you have what's called "overcurrent draw". It's the normal existence of NiMH batteries, but in a LiPo it can cause them to swell and damage the cells.

If your motor draws 16A, then you lipo should at very minimum be able to supply at least 20A continuously.

[Magwell]

Happy new year all, another update...

While looking at ways to reduce the weight of the 249 for the 2017 season I decided on two items with additional items to potentially come.

1. Removal of the forward upper rail, replacing it with a polymer barrel heat cover



2. Removal of the rear clamp from the ready mag battery compartment. If you're using a battery storage system similar to, or modeled after, my set up and would like to do this as well - it is not for the faint of heart.

2A. Here is the battery compartment as it sits now, referenced earlier in this thread as constructed from an ICS ready mag and modified ICS high cap mag.





2B. First, the ready mag needs to be removed from the stock, and the wires cut to allow full disassembly.



2C. I then used a cut off wheel/grinder to remove the first weld and then bending the frame back and forth multiple times broke the second weld. After cleaning up the welds with the grinder the ready mag only needed some sanding and paint.



2D. I then fed a bolt through the previously made holes for routing wires to ensure the alignment, located the mag where I wanted it and marked out common alignment points with a sharpie. I then used these points to make a grid on both the ready mag and stock to allow proper coordination of drilling locations for new bolts.



2E. After some trial and error I drilled four new holes, two in the stock, two in the ready mag. These were cleaned up with a file and primed/painted over. After this, two bolts were fed through and JB welded into place on the stock. Once cured, I marked the bolts, removed the nuts and ready mag, then took my cut off saw to the bolts in order to cut them down. I applied lock tight then painted over the threads to ensure the nuts would not back off.



2F. In order to fit the mag in properly, a small portion had to be notched to fit around the forward most nut and washer. After all adjustments were made, I desoldered the DEANS connectors and ran new wires, then soldered to the removed connectors.

I'm quite happy with this modification, and it brings it to my initial thoughts on how the mag would sit. Changing the orientation allows for no more flex (the clamp could slide around slightly), and the angle of the mag would cause the corner to dig into my wrist when in the high ready or holding the gun vertical in my right hand. The adjustment allows the mag to clear my wrist making it much more comfortable. The only downside is that the stock needs to be moved back one inch (one position) to allow the mag to clear the body and be removed, but this is quite minor.

Once the barrel heat cover arrives, both will be painted and integrated into the current camo.

[Magwell]

Parts arrived last week!

I ordered the G&P barrel heat cover for a few reasons...
A. It comes with the heat cover and pin
B. It was about the same price, and in some cases cheaper, than ordering a CA heat cover + pin or A&K cover + pin. This is due to a combination of over priced stock and having to buy from different retailers in some cases.
C. G&P are known for their quality externals, among other things.



The external quality I'm pretty impressed with. The pin is metal, interior frame is all metal, and plastics are thick and well made. I noticed a some draw backs though, which I'm not sure are present on other manufacturers having never owned the CA or A&K version of the heat covers...
A. The barrel clamps are riveted into place, and as they are made from two overlapping clamps, each overlapping piece forming one half, they force the cover to be slightly offset towards the left hand side of the gun.
B. The front steel portion that mates up with the pin was twisted and sat offset, partly due to A. This may have been damage during shipping.
C. The barrel clamps had to be pried apart to slide onto the MK46 barrel, due to the grooves/notches that run the length of the barrel.

To resolve the above items I used vice grips to widen the barrel clamps and create a twisted/bent portion which slides over the barrel easier. I then straightened out the front and and re shaped it to sit evenly on the barrel pin/gas block.



The last, and most important thing to note is that the CA metal gas block pin and G&P metal pin are different sizes. It took a good while to force the CA short pin out of the gas block with a hammer, the thing was in there quite well. After getting it out, the G&P pin is actually larger and would not go in. I had to enlarge the hole in the gas block only to 1/4", I did not re size the notch in the outer barrel.

See below with the front end disassembled.



After adding a light coat of tan, here is how it looks. I'll blend in the camo later in the year when we have some warmer weather.

[Magwell]

Another gearbox post...

Over the summer I was at a couple games where the FPS would spike at the chrono, and in some cases nearly too high to be allowed to play. While my chrono was reading a field legal FPS, the field chronos would peg it right below the limit and then spike over occasionally. Turns out my chrono had been shot one too many times and bit the dust haha.

So with a brand new chrono in hand, the tests yielded 353-356 FPS with 0.28g bbs (418-422 FPS with 0.20g) With the field limit being 355FPS with 0.28g a change was needed.

The simplest solution... reduce the cylinder volume with a Sorbo Pad. Deciding this would be a good idea as well for my ICS M4's as well (which are prone to upper gearbox cracks on M120 springs once you put a few hundred thousand rounds through em), I grabbed a few from Airsoft Store Canada. I had also picked up a Madbull poly piston with treated steel rack to help reduce my RPS further, and installed this at the same time. One great advantage of the Sorbo Pads is the AOE correction. I'm a little ashamed to say this is my first time using one on an AEG I've owned, but this will now be something I'm doing to all my guns haha.



A few other gearbox items to note as well:

1. The slipping bushings I mentioned in post 14 seem to be permanently remedied now with the JB Weld. No more slipping or squealing.
2. My Anti-Reversal latch is not compatible with Siegetek gears mentioned in post 13. I'm not sure any AR latch is to be honest, not unless it's hardened steel or something. What ended up happening is because the bevel gear has the smaller gears teeth run all the way to the shaft, opposed to the gradient on a normal V2 bevel, the AR latch gets worn down extremely quickly. Once worn down, it will lock into place with the force of the spring jamming it into the bevel gear. The entire gearbox then locks up as the motor lacks the torque to free the AR latch from the bevel. It took a surprisingly large effort with a screwdriver to release it via the AR release opening in the side of the gearbox. As such, my 249 is now running with no AR latch, but should be fine with the AB mosfet in there.

So, now with it all back together I hooked up my box mag and started doing some tests.

FPS was better, with a 5 FPS drop using 0.28g bbs...

Test before beginning work: 0.28g - 349 FPS (413 FPS w/0.20) & 20.3 RPS
Test after completing work: 0.28g - 342-344 FPS (407 FPS w/0.20) & 19 RPS

Quite happy going into the 2017 season with a comfortable RPS and nice buffer in my FPS



Finally a couple notes on the weight of my MK46. Note that this was not done with a precise scale, but rather a typical household bathroom scale.

1. With the reduction in box mag size, dropping the upper rail, front sight, and clamp from the ready mag my LMG is at a nice, comfortable 15.9 LBS now. Much of this can be attributed to the smaller box mag. This is fully loaded with all accessories and dummy rounds.
2. The MK46 with box mag and dummy rounds removed comes in at 13.3 lbs.
3. The upper rail weighs in at about 0.5 lbs.

[Magwell]

Update: Image hosting rectified, pictures should be visible again.

Had our first game of the season yesterday, the MG performed fantastically. Chronoed at 333 FPS W/ 0.30g bbs (345 FPS w/0.28 / 408 FPS w/0.20g). Might need to dial in the hop up a bit but other than that still holding performance and reliability from the last batch of updates.

[Magwell]

Another Box Mag mod here..

I've been toying with the idea of some kind of self-contained tracer set up after testing my suppressor style tracer in 2017 on this MG. The tracer i have is a lower end unit and had a very hard time keeping pace with my ROF. Not to say that a higher end unit wouldn't be able to, but the added weight and length on the end of the barrel were not ideal.

So over the winter I started with some googling... and stumbled across an interesting website which detailed one way of adding UV LED's to a standard M4 hop up unit to turn it into a tracer. On the 249 models the hop up is small and the access to it is tight which got me thinking of other locations which might work well... And voila, box mag came to mind. So some more googling on that and it looks like some people have added UV lights inside the 'chamber' which houses the bbs en mass, but I didn't like this idea.. Firstly it only illuminates the BBS on top of the box mag, it uses up valuable space for ammo, and it would be semi-reliable at best. So i started thinking, and came up with the following...

1. References:
A: https://www.meetup.com/Puget-Sound-A...hread/48656383
B: http://scriptasylum.com/rc_speed/led.html
C: https://www.digikey.ca/en/resources/...or-code-4-band
D: https://www.bivar.com/portals/0/prod...3TZ-XXX-XX.pdf

2. I found myself on Digi-Key Electronics and ordered some 405nm/3.3v UV LED's. I ordered ten which came in at around $30 CAD, so far so good.

3. I have tons of wire and a large number of resistors from other projects kicking around, but these are pretty inexpensive to come by, $5-15 at the Source or online.

4. First, the 3mm LEDs needed to be 'cut down' to avoid blocking the BBs, so I took a dremel to the end and then polished it to make it nice and clear again.



5. Disassembled my box mag and pulled out the insert which feeds into the hop up. After eyeing it up and down, I decided to install four UV LEDs inside the channel right before the bb's enter the machine gun. I drilled two small holes to route the wires through for the right hand LED.



6. Each lead had to be soldered to some 20 awg wire.





7. I then ran the leads down into the box mag, soldered my resistor (after calculating the required resistance rating, and selecting the appropriate resistor), and soldered in a rectifier diode to make sure that the active brake did not harm the LEDs. With this set up, the LEDs are off until I pull the trigger, and will operate in tandem with the Gearbox and Box Mag motors.

The result is a nice purple hue coming from the tube.



And so far it looks like it will work great! There is a night game coming up next week, so I'll report back on how it performed. I'll add a small switch to toggle it on/off on the fly incase more stealth is needed and also hot-glue the LEDs in place to secure them.

Video: M249 Box Mag Tracer Test

[ThunderCactus]

Nice mod.
I just put LEDs in the box mag itself, it was worked sufficiently. But being a G&P it didn't have that M4 adapter to set up LEDs. Next best thing would have been tying the LEDs to the spring feed tube.

Just tie the LED's right into the power off the mosfet, add resistors, and you'll have them come on only when the gun is firing. Add a mix of tracers and regular BBs, and you get a freaking wicked tracer effect!

[Magwell]

Thanks ThunderCactus. Yep this set up operates everything on the pull of a trigger; gearbox, box mag motor, and tracer activate simultaneously. I like the feed tube idea, maybe cutting/splicing with a length of 1/4" pvc tube to allow the LEDs unobstructed access to the bbs might also work well.

As noted in my earlier post, I reinforced the whole set up with hot glue. I also wired up a toggle switch so that the tracer can be turned on/off on a whim to prevent giving away the users position with tracers.





As for how it performed, I unfortunately only got to use it once due to the late hour the sun went down and we had total darkness (11:00 or later), early hour it came back up (3:00 am, I kid you not), and an ~2 hour maneuver by three squads for a three sided attack on our objective, a small village. When we did assault, I lit up the town like the "fourth of ****** July" providing an extremely effective distraction for my squad and the two other squads moving in. I was about 175 feet away and you could clearly see the tracers ricocheting off structures and Opfor.

I used a mix of 50/50 0.28 tracer bio and non tracer bio that worked very effectively. The four LEDs might be overkill as I think it saturates the LED as much as they can be, but I would rather have too much light and saturate it fully. For anyone considering this, I wouldn't use less than 3 LEDs.