Suomi Drum / M11 (RO) Conversion

[medphys]

This is a continuation of the RO/BETA C Drum Magazine Conversion Pics thread. It is a brainstorming thread for those of you interested in converting the Suomi M31 drum to work with the Mac series of firearms.

Please read the above, and following threads for some background info on this project.

http://www.uzitalk.com/forums/showthread.php?t=5344

http://www.oa2.org/forums/viewtopic.php?t=9134&postdays=0&postorder=asc&start=0

A big thanks goes out to Uzitalk user "strobro32" who initially started this mess and to all who have and who will contribute.

 

[medphys]

Suomi Conversion V2.0- Change to compound angle for feed tower.

Here you can see the line I drew to show the angle of the feed tower.

This is looking down into the magazine. You can see the spacer used to keep the rounds single stack. It is welded only to the feed lip on the drum with the upper end tapered to allow the rounds to feed up into the feed lips.

Also, it doesn't show the forward angle of the feed tower, but it is only about 2 degrees.

Problem 1:
The rounds are bunching at the point where they transition from the drum to the tower. There is a lot of space in this area which seems to be allowing the rounds to become offset with one another, similar to how a double stack magazine works. I'm going to use JB Weld to build up a wedge to hold the rounds down and keep them all in line.

Problem 2:
The rounds sit flat at the top of the magazine. When attempting to chamber a round, it is slamed straight into the feed ramp and stops cold. I'm not sure if I should bend the feed ramp up or not. All of my other magazines have the rounds pointing up a bit and they never hit the feed ramp.

 

[medphys]

Both the C&S Metal Werkes and Vector Uzi Suomi drums conversions I owned had a strip of nylon attached around the inside edge of the drum to give the rounds a smooth slippery surface to ride on. There's a lot of spring tension in these drums and the bullets can gall on the inside of the drum's meal surface.

There was also a forward and side cant on the feed tower which I suspect helps in the transition of the bullets as they change direction as they move from the drum to the tower.

Thanks for the info on the nylon strip around the inside of the drum. That would prevent the binding that I see on my drum. I am still going to start with JB Weld to see if that helps the feeding through the transition area. If it does, I'll go with nylon or Teflon for the liner.

The angles on the tower can't be more than 2 or 3 degrees forward and 2 to 3 degrees right (looking at the face of the drum). I doubt that the forward tilt of the tower will affect the feed angle of the rounds and it may not matter. From the pics I've seen of the BETA C mag conversion, the rounds are also flat so I may just adjust the feed ramp a bit to get them to feed.

 

[strobro32]

Another BIG thanks to 9mmsubgun-m11!

 

[fathergoat]

I actually started the project just last week myself. Since I don't have any steel mac mags yet I used a very modified sten mag for my tower. Here's what I have so far.

forward angle of the tower. dummy rounds seem to feed good from tower to chamber. Medphy's, you may need more angle here. I think that's why your rounds are being slammed downward.

cant of the tower. I tried to follow the angle of the fingers in the drum.

the fingers in the drum. Mine don't seem to be binding as much but feeding to the tower still seems a bit slow and I'm not sure it will keep up with automatic fire.

 

[strobro32]

Looks good!

Maybe somebody can chime in with the higth and width of the nylon strip.

 

[medphys]

Thanks for the great pics!

I can now see why I have binding at the transition area. The outer shell needs bent in and the curve "fixed".

By the way, the JB Weld build up I tried didn't work out. It kept the rounds from jamming, but the follower binds on the JB Weld and the inner drum won't rotate through that area when transitioning to the next coil.

 

[medphys]

Looks good!

Maybe somebody can chime in with the higth and width of the nylon strip.

And where to get them.

 

[strobro32]

We can get just about anything from http://www.mcmaster.com

It looks to be white Delrin strip.

 

[chili17]

Looks good!

Maybe somebody can chime in with the higth and width of the nylon strip.

I actually used a swd zytel mag that i cut into strips and acraglassed to the drum. You will have to sand ramps on both ends of the "lube" strips. STEn towers are one of the harder ones to get working. I got 1 of 3 I made to work 100% the other to were between 80-90% and got turned into uzi drums.

 

[medphys]

After changing the angles it feeds much better now and doesn't bind in the transition area. Hopefully I'll get to test it out tomorrow.

Next up is to order the dummy rounds and acquire the plastic lube strips. It looks like this might actually work :shocked :allright

 

[tyromeo55]

lookin good... They sent me a ups tracking number that says my drum was shipped to mu PO BOX so we'll see if I even get mine =(

 

[medphys]

And for the record, I am working with a grinder, dremel tool, cheap wire welder, hacksaw, and sandpaper. It's not too high-tech in my garage

 

[tyromeo55]

And for the record, I am working with a grinder, dremel tool, cheap wire welder, hacksaw, and sandpaper. It's not too high-tech in my garage

sandpaper can be considered high tech for some people on the board

 

[Vegas SMG]

... Mine don't seem to be binding as much but feeding to the tower still seems a bit slow and I'm not sure it will keep up with automatic fire.

The springs in these drums are old so you may need to remove the feed arm, wind the spring one additional turn, and reinstall the arm for reliable feeding. Conversely, too much spring tension may tend to bind up the rounds and result in poor feeding. Adjust as needed.

I'm glad to see several of you taking on this project. Best of luck and please keep us posted on your results!

 

[medphys]

I had a semi-successful test this evening.

I couldn't get the first 15-20 rounds to feed due to the friction between the rounds in the outer ring and the drum case. I believe this is the case because the rounds would advance up the tower, but they were way to slow; plus there was a lack of spring pressure keeping the rounds up into the feed lips causing nose dives. Once I got through those first 20 rounds, it emptied the drum in one trigger pull.

One thing I noticed is that my magazines (all of them) sit a bit low in the mag well and have about 1/16" of up/down play. My regular magazines run fine because the feed angle has the rounds pointing right into the chamber and they never touch the feed ramp. With the drum, however, the rounds are much flatter so they rely on the feed ramp to angle them into the chamber. I had to physically hold the drum up and take up the slack to get it to feed.

I do not have the lube strips yet, so hopefully that will fix the issue with the drag.

Overall, it was a successful test and this build has really proved that these projects aren't as easy as they look. The worst of it all is that I forgot to push 'record' on my video camera. :rolleyes

 

[strobro32]

Sounds like a productive day. We should start figuring out what strip to get.

Thanks Chili and Vegas for the info.

I just started my Suomi drum project today but I wanted to put a new spin on it. how does a 140 round double Suomi drum/ DF Sumoi tower combo sound? It would be neat for the Max-11 DF.

 

[fathergoat]

A friend of mine gave me some self adhesive graphite impregnated belt sander platen. It's availible here http://woodworker.com/6-x-48-belt9-disc-sander-34hp-mssu-814-253.asp?search=878526&searchmode=2
part #878526
the stuff looks rough but it's slick and it really did seem to smooth things out in the drum. In my test today I had the same problem with the first rounds nosediving. After I got through those it ran great. It may have been weak spring pressure but I'm out of ammo
here's a picture, and I'll post video as soon as it's done loading.

And for the record, I am working with a grinder, dremel tool, cheap wire welder, hacksaw, and sandpaper. It's not too high-tech in my garage

same here hifive

The springs in these drums are old so you may need to remove the feed arm, wind the spring one additional turn, and reinstall the arm for reliable feeding. Conversely, too much spring tension may tend to bind up the rounds and result in poor feeding. Adjust as needed.

I'm glad to see several of you taking on this project. Best of luck and please keep us posted on your results!

After I tried the full drum I gave it an extra turn and shot the remaining 15+ rounds I had with no malfunctions. The extra turn may help.

 

[fathergoat]

http://www.youtube.com/watch?v=dvMyJhgwJ44

 

[medphys]

http://www.youtube.com/watch?v=dvMyJhgwJ44

That runs pretty good considering you are running full speed. Strobro and I are running slowfire, so the drum doesn't need to feed so fast.