Wednesday, March 7, 2012


I haven't had much of a chance to update my blog as of late, work and classes have been hitting me pretty hard and I haven't had time to do a whole lot. I have good and bad news on the Suomi drums I've been working on converting; it seems every time I get something successful done, something else pops up to impede me.

I finally got some progress on the last drum assembly I had, and it seemed like it was going to work okay. It would feed about the last 40 rounds in a row without any trouble, and the remaining rounds were just a matter of lining the inside walls of the drum with delrin or something similar to cut down on friction. Unfortunately, I managed to mangle the outside shape of the drum a small bit. I got it pretty close to it's original shape but the cover didn't want to fit back on as needed, and since I've done so much cutting, welding, testing, and modifications to that drum, the drum winding mechanism quit latching correctly. After trying to fix the issue, I finally gave up on that drum. I just couldn't get anywhere with it, because the winding kept letting loose and smacking me. I don't know how many times I thought the drum had broken my finger for me. Enough was enough, I decided to start from scratch. I ordered a few drums from Centerfire and figured they would be sitting on my doorstep shortly. After a couple days of being impatient, I went to MGS and bought a couple more drums. Those weren't in the best shape, but aside from some rust, they did function just fine and they didn't try to remove any of my digits.
I welded another mag tower onto the new drum (though this time I welded it on center with the drum instead of off-center) and loaded the drum up with 9mm Winchester White Box ammo. I found a couple binds in the feed as the rounds ascended the mag tower, and after a couple of slices with a Dremel tool, removed the binding issues therein. I had not formed any feed lips on the mag tower as of yet, and I was curious as to how well the drum would feed with the mag tower on. I loaded the drum up again and hit the release on the back of the drum. This literally dumped the drum empty in less than 2 seconds, so I know there weren't any friction issues, or at least not enough to hinder a smooth feed in a rapid fire test. My next challenge was to design a new set of feed lips that would allow the rounds to tip up slightly and be fed smoothly into the chamber. This is where I am currently, I have half the lips designed and welded on. It seems that what I may have to do is set it up where the bolt reciprocation actually pulls the rounds backwards just slightly which in turn causes them to point upwards. Nothing else seems to make the cartridges tip up correctly in the same manner as they do in the factory mags. Trying several different magazine angles on the old drum didn't seem to make a whole lot of difference in the long run as far as how it affected the rounds pointing up. By the time I had the rounds pointing up enough to feed right, the mag was angled so far forward that it didn't feed smoothly at all. I've decided to live with the angle that gave the smoothest feed and see how much I can manipulate the angle of the cartridge feed by changing the feed lip arrangement on the mag. This is what I am waiting to do at the moment once I get enough time to work on it. On top of everything else, I've had to put a power steering rack in my car, and that has taken a couple of days to install and then try to realign the front end.

We will see how this goes. My guess would be that it is getting down to brass tacks; once the feed lip issue is solved I should have a working product. The only other issue I can see is friction, and as previously mentioned, some delrin strips on the inside of the drum should solve that. I saw on the Uzitalk thread where several others were setting up drums on their Mac submachine guns that a decent alternative to the delrin strips was the large zip ties normally used in HVAC ducting. Depending on the price of Delrin, I may just try using the zip ties for now to make sure it solves the problem. More on this as I get to it.


  1. Thanks for the update, and good luck! I had to wait a bit for mine from Centerfire, but wow! Apparently unused, in the original cosmo and paper wrappers.


    1. Thanks, FK.
      I was really impressed with the overall quality of the drums they sent me (CenterfireSystems), they were literally brand new, unused, and came with at least 100 bucks worth of cosmoline packed into them. I literally clogged up the parts washer at my job cleaning them out.

      I have the feed lips formed and welded on, I should have an idea later this week how this is going to work out.....

    2. So I assume that you'd like me to clean my own before I send them? :) Seriously, I look forward to updates on the lips.

    3. LOL!

      I wouldn't hate you if you hosed them off first with some brake cleaner. If not, well, I may have to hook my pressure washer up to my parts washer at work and reinvent the wheel, so to speak. =)