Suomi Drum / M11 (RO) Conversion

[strobro32]

I have new ZMAGs on the way. 2.0 this weekend.

Does anyone have the length and width of the aluminum tube used for the dummy rounds?

[strobro32]

2.0 has been tested. The linked cartridges feed smooth and the spring is plenty powerful at a preset of three rotations. I am running 4 rotations now. The feed angle at the feed lips is perfect.

This drum will not reliably keep up with ROF of 1600 rounds per minute of a M11/9 SMG. I get 1 or more feed issues per drum where the bolt closes on an empty chamber. I will try to tweak it and test again this weekend. I'm sure this is why the slower rate of fire of the Uzi, Colt or MP5 Suomi drum systems are more popular to make/own.

I'm sure it would run great on a slowfire system but I do not have a Max, TASK or CFW bolt to test. I need to call around. If anyone knows anyone with a SF system in Savannah PM me.

Here it is freshly parkerized.

[xdamagedx]

nice job!

[Jmacken37]

Matt, you’s a stud!!!

[Hey...]

Want.

[strobro32]

I added new pics with the parkerized finish. Thanks for the help fellas.

[Mr.Maim]

DAMN! You're my freaking hero! That looks great!!!

What made you choose that angle for the "magazine extension?" Was it entirely based on the angle of the Suomi "feed ramp" on the inside of the drum, transitioning into the stick magazine?

Just curious. (if you answered this already just tell me "go back in the thread" but I have not seen it discussed)

I have C&S Metall Werkes drums for the Colt pattern 9mm AR15, HK MP5, and UZI, and I have always thought that they performed some voodoo magic to make them reliable. Their "magazine extensions" attach at a right-angle to the drum.

[strobro32]

What made you choose that angle for the "magazine extension?" Was it entirely based on the angle of the Suomi "feed ramp" on the inside of the drum, transitioning into the stick magazine?

There are 2 angles for the tower. The 1st is the angle side to side on the drum. The 2nd is front to back on the drum. The side angle is determined by the least amount of drag the linked rounds have entering the tower. I used the angle of the bottom finger guide (that diverts the bottom of the cartridges into the tower) for the side to side angle.

The 2nd angle helps the linked rounds to transition to the correct angle of the tower's feed lips. I use the linked rounds to help find the path of least resistance. The ZMAGs are a PITA compared to the Recon Ord/PAM2 mags because the ZMAGs need a divider with a bend in it to help get the cartridges to the feed lips . The bend needs to go at the precise place inside the tower.

The number of linked dummy rounds also change reliability. The fewer the linked dummy rounds, the less the resistance. The slower the ROF, the better the reliability. Which is why MP5. M76, Uzi and Colt Suomi towers work better I think. Shorter towers are easier.

On my first attempt at the ZMAG/Suomi drum, I had more of a forward angle to the tower and the linked rounds seemed to have too much drag I thought. On this 2.0 tower, the angle was not as forward and I compensated with and extra spacer on two linked rounds to get the feed angle. It seemed to work better.

[Mackjack]

I took a guess at the angle based on two Betaco drum towers I made. The Uzi tower Suomi pictured on page 1 gave another clue.

On my first attempt at the ZMAG/Suomi drum, I had more of a forward angle to the tower and the linked rounds seemed to have too much drag I thought. On this 2.0 tower, the angle was not as forward and I compensated with and extra spacer on two linked rounds to get the feed angle. It seemed to work.

Any videos?

[strobro32]

I plan to video once I get a slowfire system to test. A CFW bolt should be here next week.

[Mr.Maim]

I took a guess at the angle based on two Betaco drum towers I made. The Uzi tower Suomi pictured on page 1 gave another clue.

On my first attempt at the ZMAG/Suomi drum, I had more of a forward angle to the tower and the linked rounds seemed to have too much drag I thought. On this 2.0 tower, the angle was not as forward and I compensated with and extra spacer on two linked rounds to get the feed angle. It seemed to work.

Ah understood, thanks for the reply!

[Mackjack]

I plan to video once I get a slowfire system to test. A CFW bolt should be here next week.

[strobro32]

I was going to post video but after three weeks of effort I can not get my drum to work reliably without at least one stoppage, even with the slowfire CFW bolt on 2 different guns. The bolt outruns the feeding of the cartridges. I think it may be the drag of the cabled aluminum dummy rounds.

On the + side, the new CFW slowfire bolt I bought to test it with, works perfectly on both guns. I will be offering it up for sale soon to recoup my investment, if anyone is interested.

[Vegas SMG]

The new prototype A bolt arrived in FL this week and will be hammered on. Next stop is you Matt.

[xdamagedx]

I think it may be the drag of the cabled aluminum dummy rounds.

https://www.amazon.com/dp/B00HAPQTUI

These plastic ones seem to work pretty good

[strobro32]

i personally think it's the ZMag tower. The taper to the feed lips makes it a poor choice for a tower. The PAM2 mags are easier to convert.

[Jonsm114]

Interesting thread....we built thousands of these for the MP5-M11, Uzi, AR15-9, M10......and a few more that we were unable to being to market because of the passing of the crime bill.....was a fun project.

Jon

[Mr.Maim]

Interesting thread....we built thousands of these for the MP5-M11, Uzi, AR15-9, M10......and a few more that we were unable to being to market because of the passing of the crime bill.....was a fun project.

Jon

Would the "we built..." that you're referring to be C&S Metall Werkes?