Umarex M712 + DEC DL44 kit build


New Member
This is by no means accurate, but I want a "live fire" DL44 and this is the closest I will probably ever come. I thought about checking to see if the M712 can be accurized, but in the end there are so many little things that are off compared to a C96 that I don't think it would be worth it. The Umarex uses 4.5 mm steel BB's and is a CO2 powered gun that only comes with a long magazine. It has a single shot and full auto option. Right off the bat I wanted to remove the shot selector and make this single shot only, but the way the trigger mechanism is put together you have to have the selector parts in place. Still thinking about that.

Video review of the gun itself:

This is what i started out with

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Then I was lucky enough to get one of the DEC kits from the latest run (parts are hot glue gunned on to see how they fit)


With all the parts in place I could start thinking about the build. The biggest obstacle is the 18 round long magazine- It takes a CO2 cartridge, no way to cut it down and still have it be functional. Marushin used to make a 6mm and 8mm airsoft M712 that came with a gas blow back short magazine. The 8mm short mag is still available from some of the retailers in Asia. The Umarex is based on the Marushin and the magazines looked close enough in the pictures that I decided to give it a try and ordered one.

After receiving the wrong mag, returning it, and finally getting the right one I looked things over. The general dimensions are very close. The 4.5 mm head will fit on the 8mm mag with no problem and aligns in the chamber. BUT

1) the short mag is wider then the original- the Umarex mag has a slight taper towards the front. Easily fixed on the sander.

2) The 8mm ammo well will have to be sleeved to fit the 4.5 mm BB. Should not be a big issue, just have to find the right tubing. There is also a follower slot I will have to cut into the mag. In the last shot below they look like they have different dimensions, but it is just the way the mags are angled.

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Magazine heads- the red is for 8mm

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The 4.5 mm head in the 8 mm magazine:


3) The locking catch on the short magazine is smaller than on the Umarex mag. I fixed this by elongating the mag catch stop inside the gun to allow it to extend out a few mm further into the magwell.


The mag will now slide in and catch with no issues and is lined up within the chamber. First picture is with the top half of the gun removed, second shows the mag in the firing chamber.

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And finally it fits.

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Note the way the grill fits- the M712 has a flat front where the C96 is more rounded. I have not decided what to do about this yet. I plan to strip and blue the entire gun so I can't just use filler to round off the front end.

The majority of the barrel is held on by one allen screw. Fitting the bull barrel on this thing is a breeze.

I will update this as it goes, tomorrow I am going to work on the E-11 for a while...

Thank You


New Member
Hi Mark
I just got my KWC m712 today and ordered the DEC kit on friday for delivery end of June. I am also trying to get a hold of the Beta Project sterling as well. Im in Canada so this stuff is a PITA to get but Im getting close.

Im interested to see how your build goes. Will you be putting up more updates?

I also have a question about your Umarex? Is your magazine and magazine well trapezoidal? Meaning thinner at the front and wider at the trigger guard? you said yours is tapered? It seems to me that that is the only fitting problem except having to shim the scope bracket for the difference with the magazine housing. From Your pictures I think my KWC and your Umarex are from the same factory :) Im gonna be shoving in a blaster core for sound and lights in the mag well so I won't be doing a mag like yours but did you get it to fire yet with the shorter mag?

How do you like the beta sterling? Are you going to do a build log on the E-11 as well?



New Member

Trapezoidal is a good way to phrase it. I have the basics worked out. I was able to modify the short magazine to work on the Umarex by replacing the trigger and recoil springs with lighter weight springs. The CO2 has more energy than propane or green gas (pretty much the same thing from my understanding) and the latter would not re-cock the hammer. I still have to get the BB feed dialed in but for the most part it works pretty well- right now I can shoot 2 or 3 bb's before the feed in the magazine jams. The kick is much less than using CO2, but that's ok.

I suppose if I could figure out a way to put an ignition source in the flash hider I could even get a nice flash out the end. How that would work I have no idea...

I would like to add some blaster sounds, but the only place to put anything would be inside the grip. I have a 20mm speaker and the sound board from a min-blaster that I am pretty sure I could shoehorn in there, but it is much too quiet. Anyone know if there is a mini-amp that would somehow work?



New Member
Here's a quick vid of the converted gun with no BB's in the magazine. There is no follower catch so the bolt will not remain open when out of BB's, it will keep firing until the magazine uses all the gas.




New Member
It looks like fishmeok got everything working properly (I'm assuming this is his yt-channel):

...The 8mm ammo well will have to be sleeved to fit the 4.5 mm BB. Should not be a big issue, just have to find the right tubing.
What exactly did you end up using to shim the 8mm cavity to accept .177 (4.5mm) caliber BB's?
I realize the short mag only holds 5 BB's but does the modified mag cause any jamming when the airgun is set to automatic?

...There is also a follower slot I will have to cut into the mag.
I don't see anything in the OP's photos. Is there any more info on this? How has the modified short mag held up over time?

...Note the way the grill fits --the M712 has a flat front where the C96 is more rounded. I have not decided what to do about this yet. I plan to strip and blue the entire gun so I can't just use filler to round off the front end.
What did you end up doing here?

Also, did anything come of the following?
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New Member

I have not progressed much beyond that point yet, but the magazine has held up well so far. I ended up using a disposable pen housing (about perfect for the 4.5 mm BB's) I cut a slot for the spring follower and experimented with springs until I found the correct pressure. It holds 9-10 BB's and for some reason tends to shoot a BB every other time the gun cycles. I also put a weaker hammer and recoil spring in to allow the gun to cycle completely using green gas or propane. If you use the heavier CO2 springs it will only partly recoil and go into full auto.

The other vid was just to show how flammable green gas is. It would be fun to figure out a way to put a heating element in the flash hider to ignite when the gun fires, but there is no room for an element, wires, and a battery. Unless maybe one of those tiny drone batteries..



Well-Known Member
Hello fishmeok

Great Work So Far!!! I was also wondering what your thoughts are on the Grill for the wider and flatter M712? I have all the parts lined up for a build using this version as a base but every time I look at the Grill I am at a loss. I found some dryer tubing at Home Depot that "sort" of looks the part with the proper width but there is a definite gap that just doesn't look right. Any pointers or hints would be greatly appreciated.

Thank You



New Member
Wow, that's looking awesome, mate!

I won't go so far (the fire thing), I've just bought an HFC and the short mag will (eventually) come from Cobra Airsoft... I'm working in a 3D printable kit by myself, at this time I only got the bull barrel and silencer.

May I ask you a question?. Is the canon removable, and how? Did you had to cut?

Thanks a lot,


New Member
I only got the bull barrel and silencer [flash supressor].

Where did you get the barrel and suppressor?

Is the canon removable, and how? Did you had to cut?

By canon, I assume you mean the barrel?
The barrel of the Umarex M712 is not designed to be removed. Cutting the barrel off any airgun (.177") or airsoft (6mm) will render it useless as a firearm.
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New Member
I'm designing it myself, adapting my old ANH kit, it's not 3D printed yet, but I like by now. The new grill is totally different, the cuts are symmetrical and it's more like a saw than a radiator. I have to model it, maybe this afernoon. This is the look with the classic grill.
You assume correctly, sorry my english. So, you had to cut...

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