Anyone else see the article in the april 20th SGN about the suomi based 9mm rifle? It looks pretty straight forward and the guy said he built it for about $175. I'm sure I have a complete spare set of AR15 fire control parts which would bring the price down as well as various other scrap that could be used. I think I'll order 2 suomi kits and give it a try.
If your brother works for a tool and die company then he has all the tools that make this a lot easier to build. Turning down the bolt isn't the hard part of the bolt mods. Its the change to a firing pin or striker system that most people have trouble with. There was a article in sgn a few years ago that showed a semi sten being built and had the bolt mods for that in there. The way a sten bolt is made, it may be difficult to change to semi auto without switching to a different recoil spring setup. Look at the prexis or indiana ord web sites as they have semi sten bolts you can buy which may save you a lot of trouble. But at the same time if your brother is willing to make you one, then I'd go that route.
He said that it would only be easier due to the groves cut on the bottom of the bolt, something about having to "block cut it then put it in a lathe", something like that, but also I would lose a lot of the mag groves. Its all too technical for me.
I'm pretty sure you're going to have to go with a larger id receiver tube if using a sten bolt as you can't turn it down to 1" with out cutting into the extractor. For the suomi bolt I anneal it, drill out the firing pin channel with a drill slightly smaller than the firing pin and drive out the firing pin, turn the bolt between centers, then chuck up the bolt and drill out the firing pin channel to set firing pin protrusion, mill hammer slot, install and trim firing pin bushing, finish drilling firing pin channel, drill firing pin retainer hole. Hope that helps.
I've had a sten kit for about 22 years now that I'll build soon. Here's a picture of the sten bolt next to an semi modified suomi bolt. You can see the hammer slot would extend back into the spring guide if you went with an ar15 firing pin. You might want to look at shorter firing pins like a 1911 or m1 carbine. The hammer slot would still be the same length (maybe a little shorter) but it could be moved forward. Thats what I was planning to do when I modify my bolt as I want to use the big coil spring to keep the clasic sten look.
Yes it should! I haven't got the firing pin retainer drilled yet on that bolt. Theres a picture a few posts back that shows a completed bolt. I was out shooting the 98%completed suomi build today so that bolts all dirty!
Yeah I just realized that when I removed the pin from the extractor, sooooo it looks like I'll be buying a suomi bolt anyway. you recommend anyone in particular, I know copes has them for 24.99, any place got them any cheaper?
$25 is a bargan for what you get, and copes have a well earned good reputation. Why not just go with a 1-1/8" or 1-1/4" receiver tube. The sgn-9 design is more like a guide, and after all its your gun build it like you want it.
No, Its not like I want to "copy" the SGN 9 design I just happen to like the thinner, sleeker design that is depicted in the article over the rather robust sten or suomi design. Part basic tube, part AR, its a very easy simple starter. I already have some ideas to alter the SGN 22 design to characterize the AK a little with a savage mag in mind. I just didn't want to make one without the other, besides I want to do all the work myself, for the knowledge and experience, rather then buy a "kit" or "assemble" manufactured parts.
Hey moleman I was curious about the barrel that I bought. Its a 10" Uzi barrel, I know that the barrel has this half lip about 3- 3 1/2" behind the muzzle due to the design of the Uzi. Now it may be a stupid novice question, but that doesn't affect the length according to the laws does it. I knew I would have to at least add 6" but I don't have to add like 13" to it do I. The way I was going to hide that lip was to use it as the lock for the barrel, if that makes any sense, with the shroud, or just remove it and make like a trunnion and pin it in place. But I kind of like the idea to not pin the barrel permanently so that I can separate the barrel, the upper and lower receiver so I can put it in this little silver padded case in pieces, kind of what you see in the movies, I think that would be cool.
ATF measures bbl length on a semi auto by dropping a rod down the bbl until it rests against the breechface of the closed bolt. The shortest point on the muzzle end is marked on the rod and then measured.
The Kernel is right on the money! If you're going with an uzi barrel and are planning to use a tube type receiver and a takedown/removeable barrel then it would be a good idea to modify the barrel stub by turning it down slightly so as an unmodified uzi barrel can't be placed in your gun. For some reason the atf has a wild hair up their butt about tube guns and short barreled rifle violations. If you read the current "suggestions" they give you on building a tube type gun its going to list removing the feed lips on the bolt and if it has a removable barrel it should be modified so an original unmodified barrel cannot be inserted. I removed the feed lips from my suomi bolts and I turned down the suomi barrel stub from about .780" to .750" plus I made the indexing nub on the frame half again as big. There's no way an unmodified suomi barrel is going to fit in my receiver. Of course this is just my suggestion and not anything that would help you in court. Its always best to write the atf with any build legality questions.
I roughed out the barrel bushing and made it so I can cut the barrel jacket lugs into it. I have the ring for the lugs final sized for height and length. When I measure an original lug it comes to .419" near the bottem and .455" at the top. I'll try for the .455" and If I need to, undercut it. I'll use the tape method to lay out the lugs since I don't have a dividing head. I'll have to clean up the space between the lugs with a grinder. The barrel bushing id is .75" so I will turn down the barrel stub to match and make the index nub larger to prevent the insertion of an unmodified barrel.
I cut out the lugs in the barrel bushing for the barrel jacket today. I left the area in front of the lugs long so I can decide if I want to turn it down on the lathe and then weld on the indexing nub, or mill it down for the barrel leaving the indexing nub. On my first build I turned it down on the lathe and then built up an area with weld and then filed it into the index nub. To lay out the lugs I took a piece of scotch tape and ran it around the collar where the lugs were going to be making sure I overlapped the ends. I then cut through the center of the overlap and removed the excess tape. Next I put the tape on a piece of square stock starting on an end corner and colored it black. I measured the tape with dial calipers and since I wanted the 4 lugs to be around .455" I subtracted .182" from the tape length then divided what was left by 4. I then alternated adding the measurements and scratched off the black magic marker from the tape at each measurement with the dial calipers. I then placed a second piece of tape over the first to keep the magic marker from being rubbed off. I then put the tape back on the lug collar and using a small piece of angle stock as a guide I cut through each line in the tape and removed the larger sections leaving the .455" tape correctly spaced (or close enough). I then put the barrel collar in the milling machine and squared up the lug on top. I cut each lug out by first cutting the front cut until I could see the cut touched the tape, then used the dial calipers to cut the back side until it was .455". I got some a few thousands undersized I think because I didn't clean the chips out real good. Oh well I will next time. I then used a air cut off tool to grind out the spaces between the lugs. I mounted the barrel bushing on a section of scrap rod so I could rotate the bushing slightly and grind from lug to lug while keeping the tool stationary. When I thought I had it done I sharpied the ground area and tried putting it in a barrel jacket. I had to remove it and hit the high spots twice before it dropped right in smoothly. It didn't turn out near as nice as what the Finnish did 70-80 years ago, but its functional. The top pic shows the lugs/barrel bushing and receiver tube, the bottem one shows the 1.5"x.188 wall receiver stock, and 1.25"x.250" wall barrel bushing stock.
Thanks, I have seen suomi receiver blueprints on gunbroker from some guy in canada, but I'm just getting my measurements from my demilled kits. Prexis sells a 80% receiver, but I kinda like making my own parts.
You might try over at weaponeer for a bolt drawing, but I don't recall seeing one anywhere. A guy there (Finnguy I think) made one and you might be able to get the drawings from him. You can buy a bolt from copes for $25 and turn around and sell it to get your money back when you make your drawings. For $25 I wouldn't try making one. I also haven't seen a suomi extractor for sale except from a guy in finland and he ran out of them a year ago or so.
Hey moleman, wanted your opinion on this. The pic is a two piece front trunnion that I'm thinking about for my take down 9mm. Not sure if it will work or if it is safe enough, if I should use 4130/4140 or if I can use mild steel or aluminum, just to keep the wait down. I like your build so far.
It looks like a good idea that would work. In the sgn-9 build IIRC Matthews used two takedown pins to hold the upper and lower together. You may want to thread enough of the barrel for a knurled lock nut like a savage uses. This would help compensate for any wear or looseness from the threads and keep the barrel tight for better accuracy.
Well that is just the front trunnion, for the rear I was just planing on welding a piece of steel to the upper receiver to except a pin for the takedown, modled after the AR.
I went ahead and finished my sgn-9 bolt that I started a while back. Its 1" diameter for the sgn-9 standard tube, but with a car length recoil spring guide.
I see that you have your charging handle in two pieces I was just wondering are you planing on making it permanently attached, or is that the only way you will be able to remove your bolt?
The bolt handle is just like the sgn-9 article which is copied straight from a sten design. The sgn-9 bolt handle is removable, but is held captive except for a spot at the end of the cocking slot where the bolt would not normally extend to in recoil. The bolt handle acts as a bolt guide, and after the recoil spring is removed the bolt is alowed to go further back than it normally would in recoil to a spot where the charging handle slot is opened up from the skinner area between the two bumps about in the middle of the handle. You really don't need the outer bump, but it can keep your finger off of the cocking slot and avoid cutting it on the sharp edge.
I got a little more work done on suomi #2. I extended the barrel to 16-1/4" by turning down the last inch to a thousands over the .584" hole I drilled in the 3/4" diameter extension with a 37/64" drill bit. I welded the extension on and turned down the welds in the lathe. Then I cut down the barrel stub to .750 and inlarged the index slot on the barrel collar to 1/4". I ended up cutting the index pin on the barrel bushing on the milling machine. I made a tight fitting collar for the barrel bushing that had a cut through one side so it would tighten up on the bushing in the vise and milled two flats on the collar. I then tightened the barrel bushing up loosely in the mill vise and hooked a dial indicator to the mill head and ran it around the top of the barrel bushing. I adjusted it until there was less than a thousands movement on the dial indicator. I had previously scribed a 1/4" "pin" location centered above a lug. With a 1/4" 4 flute end mill I cut off 20 thousands at a time until I was a few thousands over the measurement from the back of a lug to the front of the barrel bushing on a demilled suomi stub. Then I would move the table all the way to one side and test fit the barrel and shroud on the barrel bushing without removing it from the vise. When it would fit I was done. I had previously opened up the end of the barrel shroud for the barrel to fit through by cutting off the barrel looking nub at the end, and drilled/bored it out until it was a few thousands over the barrel extension diameter. Heres some pic of the work.
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