Suomi Drum / M11 (RO) Conversion

[Jmacken37]

Here's a 3 1/2 minute video of loading and burst firing the Double Suomi Drum.

Matt,

YOU are SOOOO COOL! Fun to see you again even if it's only in a video!

Jake

 

[strobro32]

I'll never be able to touch your coolness Jake with that select fire Siags 12.

 

[shawnr1]

I'm getting motivated to attempt another Suomi Drum Conversion. I need to purchase my own tools.

How about a list of mandatory tools?

 

[medphys]

In the order I use them:
Hand held grinder
Dremel tool with small cut off wheels and mini grinding wheels
Large metal file
Small file set
Hack saw
Multi grit sandpaper
Welder

 

[greenpeas]

I used this project as an excuse to buy a bench grinder. The harbor freight store had them on sale for less than $50. Works great for grinding off feed lips and adjusting the angle of the tower. Plus, you don't risk denting or bending your drum/tower by clamping it in a vice when grinding.



Miller 135 MIG welder
cordless drill
air cutoff tool (probably not essential but great for cleaning up welds)
Hacksaw
steel files, needle files
sandpaper, scotchbrite pads for polishing
old half full can of VHT header paint
clamp things to hold the zip ties while the glue sets. (you could probably use clothes pins)
plenty of cold beer & band-aids

 

[fred9x21]

You guys have inspired me!!! I ordered 2 drums and I am waiting on Jerry to get a few more RO mags. Then I will be ready to test my skills.

 

[Jesse454]

After i seen those drums work i had to make one. Well i made it and it looks good but it seems like the top round catches the rim of the one below it. It has not been tested yet. Any tips on how much forward cant and any details on spacer that is used in the RO mags.

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[medphys]

the top round catches the rim of the one below it. It has not been tested yet. Any tips on how much forward cant and any details on spacer that is used in the RO mags.

Cool!

Your front-back angle looks good, but the left-right might need increased a bit. It may work just fine for you though, you won't know untill you test it.

The "rims catching" is something I experience too, but I think is normal and I don't have any problems with it. I really think it's only noticable when you strip them by hand, not when it's run in the gun.

If you are talking about the spacer to make the rounds single stack, I use a piece of flat-bar from Tractor Supply. It is about 1/8" thick and 3/4" wide. I use a hand grinder and large file to taper the top part so the rounds transition smoothly from the tower up to the feed lips.

I weld it to the drum first to set the angles, then fit the tower to the spacer.

Hope this helps a bit.

 

[Jesse454]

Thanks Medphys!

I don't know how many times i changed the angles because i thought something was wrong. I need to add the nylon zip tie before test. At first i used 1 - 1/8x1 flat bar then i changed it to 2 flat bars its the same with 1 or 2 didn't make any difference.

 

[fred9x21]

Having trouble getting mine to run. I haven't got the zip ties in yet but I don't think they will change the problem I'm having. My front to back angle is 20 degrees and I've tried 2 different left to right angles. ( the photo is of my second attempt) I used 2 - 1/8" spacers, one on each side of the mag so the rounds go straight up to the feed lips like a single stack. The problem I'm having is the rounds are going up the mag flat instead of nose up and the bullet is hitting just below the feed ramp and not going up the ramp. Any ideas? I'm going to get some zip ties and get them glued in but I don't think the problem is friction.
Thanks

 

[medphys]

Having trouble getting mine to run. I haven't got the zip ties in yet but I don't think they will change the problem I'm having. My front to back angle is 20 degrees and I've tried 2 different left to right angles. ( the photo is of my second attempt) I used 2 - 1/8" spacers, one on each side of the mag so the rounds go straight up to the feed lips like a single stack. The problem I'm having is the rounds are going up the mag flat instead of nose up and the bullet is hitting just below the feed ramp and not going up the ramp. Any ideas? I'm going to get some zip ties and get them glued in but I don't think the problem is friction.
Thanks

That seems to be the biggest issue I have with building them. The first two I built worked well, the most recent one is having the issue you are. I'm going to grind the feed lips to let the rounds point up more and maybe change the tower angle a little more and see if it helps.

Also, make sure your magazine is sitting high enough in the magwell so the feed lips sit as high up into the bolt channels as possible. I had to put a small spot weld on the magazine where it catches the mag catch on the gun then grind it down a bit. This will let the rounds sit higher up and get them closer to the feed ramp.

I wonder if tweeking the gun feed ramp might help a bit. Problem is, I tried tweeking mine tonight an broke the trigger pin issed

 

[fred9x21]

After reading your reply I got my gun out and was looking at the feed ramp. I could see where the rounds hit. I got out the dremel and the 1/2" drum sanding bit and reshaped the feed ramp. Then I polished it to a mirror finish. I think this will help. I am going to glue in the zip ties also, then give it a test run. I'll report back as soon as I can get to the range.

 

[Magoo]

I wondered why you quit Shooting earlier!. Sorry to hear that!.

I wonder if tweeking the gun feed ramp might help a bit. Problem is, I tried tweeking mine tonight an broke the trigger pin issed[/QUOTE]

Yep. We heard you for awhile then it went quiet. LOL. Don't use the trigger to pry from!
Those pins are like Illegal Aliens. Just a bit of Abuse, and they Break Easily!:jester

 

[medphys]

Don't use the trigger to pry from!

Uhhh, yep. I heard a little 'click' and noticed the trigger was a little crooked. Whoops!

 

[medphys]

After reading your reply I got my gun out and was looking at the feed ramp. I could see where the rounds hit. I got out the dremel and the 1/2" drum sanding bit and reshaped the feed ramp. Then I polished it to a mirror finish. I think this will help. I am going to glue in the zip ties also, then give it a test run. I'll report back as soon as I can get to the range.

The only time I've seen marks on my feed ramp is with the drum. My regular mags never touch it. That leads me to believe that the feed angles are poor with the drums. They really need to point up into the chamber and not into the feed ramp. This is the hardest part about these drums.

Another thing to do is use a flat disk grinder on a dremel tool and grind the inside of the feed lips so that the rounds sit as high as possible in the tower. Anything that get the rounds high in the tower will help.

 

[medphys]

eep Any updates?

 

[fred9x21]

I worked with it a little last night. I believe the feed ramp work helped some, but I wasn't able to live fire it. I removed the firing pin and cycled the gun by hand and only had 3 stoppages. The rounds tipped up too far and hit the top of the barrel.

I was looking at one of my RO mags and stripping rounds by hand. I noticed the rim of the top round never caught the round below it. I also noticed that on the mag I have welded to the drum, that the second round was pushing out the front of the mag from the force of the top round pushing it forward. I got to thinking. would it be better to remove the spacers and weld the mag center on the drun opening and let the rounds feed up the mag in a double stack pattern? The mag is designed to be a double stack, maybe it would feed correctly that way.

What do you think?

 

[greenpeas]

All the successful conversions I've seen use a divider in the magazine. I would think going divider-less would be asking for trouble. Have you tried adjusting your spring tension? You may have too much?

How many clicks are you using for pre-load? I've been using around 16.

I'm not working with R/O towers so I don't have much experience with them.

 

[medphys]

All the successful conversions I've seen use a divider in the magazine. I would think going divider-less would be asking for trouble.

Agreed. When the rounds go double-stack you'll get a lot of binding as the rounds push against each other and rub on the inside of the magzine. Having them single stack eliminates most of the friction in the tower.

How many clicks are you using for pre-load? I've been using around 16.

Same here. I haven't got one to run with out 4 or 5 turns. It would be nice if the spring assembly had another bracket for the pusher so you could tailor the adjust the spring better.

I'm not working with R/O towers so I don't have much experience with them.

.

 

[medphys]

The rounds tipped up too far and hit the top of the barrel.

I've seen this happen when the feed lips are too short. The rounds pop out of the magazine too soon and are pushed up too early in the cycle and get caught on the top of the barrel.

I made a list of common feed problems for myself to try and help fix some issues as I come across them. It's not necessarily for the drum conversion and may not be totally correct, but it helps me out. Feel free to edit or add to the list.

Rounds nose diving into magazine
-dirty magazine
-binding follower
-weak spring

Rounds jamming/hitting feed ramp/lower area of chamber
-magazine too low in magwell
-feed ramp too low
-feed angle too small
-feed lips too long

Rounds jamming/hitting upper area of chamber
-feed lips too short
-feed angle too great

Rounds not stripping from magazine
-feed lips rough
-magazine too high in magwell (feed lips rubbing on bolt)
-spring too tight
-weak recoil spring

Rounds popping out into ejector port area
-feed lips too wide
-feed lips too short

Empty casing in ejection area/port
-ejector rod too short/long
-extractor worn
-extractor spring weak