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SGN-9

33K views 295 replies 32 participants last post by  moleman 
#1 ·
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.
 
#181 ·
Pic for VZ58, The ones on the left are rear fillers and are available from gunparts corp for the moment. The one on the right is a front filler and everyone seems to be out of them right now. VZ58 I can't send you the blueprints because it says your pm box is full.
 

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#184 · (Edited)
I've been having fun getting the suomi dirty the past week or so. I got it fitted for the drums and made a new disconnector and put a new firing pin spring in. When the gun got dirty The disconnector was sticking in the up position and disconnecting the trigger bar. I simply made a hump at the top of the new disconnector which sticks up into the receiver. When the bolt comes back it now pushes down the disconnector allowing the trigger bar to reset when you release the trigger. I also shortened the disconnector about 3/8" to give it more leverage to push the trigger bar out of the way. It now has the same snap of the sear resetting that the 870 trigger group had.
The second thing I addressed was the firing pin spring. The one I had in there was too weak and was allowing the firing pin to slightly mark the next round as the bolt stopped. I ended up swapping out the weaker spring with what I thought was a AR15 buffer detent spring (because it was in my ar15 stuff) but it is too large to be a buffer detent spring. Whatever the spring is it is much heavier and prevents the firing pin from moving unless the hammer hits it. The original sear spring works well also for a firing pin spring and that is what I'll use in my next build. Even with the heavier firing pin spring the hammer spring still has enough power to hit the primer as it was with the weaker spring. Here's a picture of new disconnector design and a picture of the drum installed. It looks like the new disconnector is a different angle from the first, but if they're held side by side the only difference is the length and the hump on the top of the new one. The scratch on the hump of the new disconnector is how much of it sticks up above the trigger group frame when its in the down position.
 

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#185 ·
Moleman, I went to the gunshow last weekend to pick up some things including an AR-15 firing pin and I totally forgot to get it. So as soon as I can pull my head out of my arse and get one I'll get back to you. P.S. sweeeet build!
 
#186 ·
Thanks Mtdew, I could machine the bolt for the firing pin and you could get one later if you want. They SHOULD all be the same. Its the should part that I worry about though.
 
#187 · (Edited)
Here's a LITTLE bit easier way to get the fireing pin out. I first removed the firing pin retaining pin and annealed the bolt. I used this - Harbor Freight Tools - Quality Tools at the Lowest Prices propane torch form harbor freight to heat the bolt up and it did a wonderful job. Replace the firing pin retaining pin, then drill out the firing pin channel from the rear using a extended 11/64" (.170") drill bit. The firing pin is about .9" long so make sure you drill into the back of it, but I wouldn't go so deep as to drill into the retaining pin. Remove the retaining pin one last time and take a masonry nail ( I used a 2-1/2" remington nail for a 22lr driver set with the point removed) just make sure its smaller than the .170" drill bit so it won't get stuck. The masonry nails are heat treated and make good disposable punches. I dropped the masonry nail into the rear of the bolt and put a section of 3/8" rod on top of that. With the bolt secured in the vise I hit the 3/8" rod twice with a 3lb hammer. On the second hit the firing pin flew out and went under the work bench. Since you drilled into the back of the firing pin it relieved some of the pressure holding it in, and you can use a larger drift to remove it. I then tapped the bolt with a #12-28 tap as in the original sgn-9 article. The original firing pin hole seemed on the tight side for this tap and I tapped it while it was in my lathe with the tap handle supported by a center to keep the tap straight and hopefully keep me from breaking it off in the bolt. I spent a couple days looking for a #12-28 cap screw before making one out of an annealed valve stem. Fastenal Home | Fastenal has them if you want to order them part #23198 for a 1" cap screw at $1.13, or #23249 for a 1-1/4" cap screw for $1.36. I'm waiting on my milling machine to mill the hammer slot out.
 

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#189 ·
Muttman, I made those extensions for this project over the summer. I used landscape nails turned between centers to make them true then drilled the "nail" with the bit I wanted to use about 1/2" deep then soldered them in with plumbers solder and flux. I roughed the drill bit shank up with 80 grit sand paper before I soldered them in. I haven't had to resolder one yet. The one in the picture looks bent for some reason, but it isn't, some trick of the camera. I may go back and tap the bolt on my first build for a #12-28 firing pin bushing as well, but its held up fine for about 500 rounds so far.
 
#191 ·
That should work great. I don't have a welding torch to braze so I soldered them. back on post 77 I think I showed all of the lenghtened bits I used. A couple of them have a step in them so the smaller shorter bits can reach deep enough inside the bolt.
 
#193 ·
Sorry for putting this in your thread but thought you'd be interested Moleman.

In the new SGN they are doing a SGN-22 build, yes 22lr, using a 10/22 barrel.
I was just looking at it this morning while the kids were having breakfast and wondering if it would work with a 17hmr. I think the bolt design could easily be adapted to work with a standard ar upper with a 17hmr barrel and using the stock ar buffer and recoil spring. That would cut a lot of the work off of the build. The only draw back I see is magazines for that. The 10/22 magnum mags are too fat and the rem 597 17mhr/22mag magazines suck. I suppose the savage bolt action mags would work. With the price of sub gun kits getting higher perhaps we'll be forced to resort to making our own bolts. Most of my free time lately has been consumed by getting the milling machine set up. I hope to have a flury of suomi activity when I get it going and feel confident enough to use it on gun parts.
 
#197 ·
I'd probably do the extractor cut pretty early in the bolt steps. I'd set the retainer pin hole back a few thousands so if I'm off I wouldn't screw it up. Then you could turn down the bolt face to match the extractor. I didn't find drilling out a suomi bolt for an ar15 firing pin to be too difficult. You do have to go slow and check your measurements often.
 
#201 ·
btw, thats good advice!!!

i drilled the hole that the head of the fp hits as a stop a bit too deep, allowing the taper at the very front of it to peen in the bushing and wedge itself forward. it was easily enough fixed though wiht a washer/spacer of the correct thickness slid over the fp to take up the extra space.
 
#198 ·
Back in the day there were several semiautomatic "sorta copies" of the Thompson SMG that were just tube based guns with various potmetal and wood grips added to resemble the outline of the Tommy. The bolt's were very simple, just a large diameter roundstock that fit the tube. The front section was turned down to a diameter barely larger than the casehead and a pocket for the case formed by plunging a centercutting endmill of the right diameter into the end of it. Extractor was a simple bent piece of springsteel that fit in a groove down the side of the small diameter section. One example used a screw to secure it, another used a two piece bolt and the extractor was captured by fitting inside the larger section, a pin held them together.

Even without a lathe, making such a bolt out of 2 different diameter round bars would be possible.
 
#204 ·
thank you!!

progress has slowed down since it was functionally completed. i gotta get motivated to get the finish on it. illl be sure to put it up here when i do get it done. im going for something new for me, camo finish. hopefully, it will work out!

yeah, if i would have not put the bushing in, i could have tested the fit of the fp when i was drilling the big "stop" hole, but i put the bushing in first, so the depth of the hole was pretty much a guess, as i couldnt put the fp in to check the depth. live and learn!! you got it right the first time though!
 
#205 ·
I ordered some 1" #12-28 cap head machine screws from Fastenel for the firing pin bushing, and they came in today. I made a drilling jig to drill the firing pin tip hole and partially drill the larger step behind it. I turned a piece of 3/4" rod and drilled and tapped it for the #12-28 screw. I figured it would be easier to drill the machine screw accurately if it was closer to the headstock. In order to drill the bushing after it would be installed, about 4-5" of the bolt would be sticking out of the chuck. Plus I didn't want to run the risk of breaking off a bit or screwing it up and end up with a stuck bushing in the bolt. The drilling jig worked like a charm. I tighten up a screw in the jig, then driled the screw head with a very small center that has a 1/16" tip on it. Then I drilled about 1/2" into the screw with a 1/16" drill bit. I then took the jig with the screw in it out and flipped it around so that the screw tip was facing the drill chuck and drilled it with a 7/64" bit about .6" deep until I reached the smaller 1/16" hole. I will have to deepen this hole after I install the bushing to get the firing pin protrusion set. I previously drilled the larger firing pin stop from the back of the bolt with a 0.4" bit so that between .035-.040" of the firing pin tip came through the bolt face. When I tapped the bolt I ran a 11/64" bit through the front of the firing pin hole to remove the constriction behind the original firing pin. This way when I drill out the firing pin bushing to set the firing pin protrusion I only have to worry about the firing pin hitting one surface until the 0.035-.040" number is reached. You will have to make sure that your bushing is less than .8" or drill it out from the back so that it is or the second step in the firing pin will hit the bushing. Here's a picture of the drilling jig and the firing pin in the machine screw, and a picture of the bolt with the untrimmed machine screw installed. I'll have to locktite in the screw and turn the screw head off in the lathe.
 

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#206 ·
I ordered some 1" #12-28 cap head machine screws from Fastenel for the firing pin bushing, and they came in today.
Huh, that's what I did too, same size and everything, just remember that the screw is probably really hard, I cut it flush with the mill, and sparks came off of the endmill, luckily it was a beater endmill it was already dull, and blued from overheating...
 
#207 ·
The #12-28 is what Matthews used in the sgn-9 article. At a buck 13 each its not worth the time for me to cut more even though its a oddball size. He didn't pre drill the screw before installing it though and I think doing so will help lessen the chance of screwing it up. On my fist build I used the original firing pin drilled out to make a bushing. In order for the firing pin to work I had to set back the second step or the firing pin wouldn't have enough protrusion. I really like this setup and most likely will tap the first build bolt for a threaded bushing.
[486], do you have any pic's of your build?
 
#208 ·
At a buck 13 each its not worth the time for me to cut more even though its a oddball size.
I just found a few, and the thread looked fine enough that it wouldn't back out from the pressure of the primer...

[486], do you have any pic's of your build?
Nah, I'd rather not post definitive proof that it isn't fake, what with the political climate... Sorry, you could PM me for details, but I have no pictures...
 
#210 ·
a $1.13 each you may need to find a diffrent vender or try a 5 or 6 in 1.5 pitch mm size I think a 6mm would be a better fit and common. $1.13 is way over priced I ask my vender at work the other day and the qute I got was $.25 ea. up to a 1.5" lenth.

muttman
I was thinking about the metric sizes also before I realized I was going to have to order these things. You'll have to stick with a fine pitch as there isn't much metal between the firing pin and ejector slot though. I've got the taps for the #12-28 and a bag of the screws now. I'll stick with them as it doesn't add that much to the cost of the build.
 
#211 ·
if you are tooled up for a 12-28 you would add cost to conver over. Im planing on using a 6x1.5mm fine thread and it is just under .25".
BTW did you lock the screw down to the 3/4" jig when dtilling the firing pin hole out. I have had problems with screws moving when trying that type of jig in a lathe.
muttman
 
#212 ·
No I didn't lock it down. I tapped the hole so it wasn't quite deep enough and tightened up the screw in the jig so it was stuck in there tight. I drilled out the head first, then fliped it around and drilled out the back. I went slow because I was concerned about it loosening up, but it didn't. I suppose I could drill it for a set screw and drop a lead BB in the hole to protect the screw threads if its a problem. Yesterday I went ahead and loctited in the screw with red loctite and turned the head off in the lathe. If anything turning the head off would tighen in the screw more so I figured it was ok to turn the screw head off before the loctite was set. Since the locktite hadn't fully set I'm waiting to finish drilling the first and second steps back from the firing pin hole today. I tapped the hole on this bolt the full depth of the tap which was more than the .8" or so of the original firing pin. I'll have to drill the second step first, using my first converted bolt as a depth guide. The depth of the second step back from the firing pin hole in that bolt is actually deeper than it needs to be on the first bolt. If I set a drill stop on the lengthed drill bit to drill the same depth and drill this bolt I should be good to go. That way I'll be back to just having to deal with one shoulder depth (the first step) as the firing pin protrusion limit has already been set by the last shoulder of the firing pin channel. On the next few bolts I'll just tap the bolt hole about 3/4" and I'll be back to just having one final depth to worry about for drilling out the firing pin protrusion.
 
#213 ·
I finished the bolt today except for the firing pin retainer. I don't like the set screw retainer as used in the sgn-9 (I keep thinking it will loosen up and jam the gun) and don't really like the ar15 cotter pin retainer either. Would a roll pin going completely through the bolt work or will the firing pin and spring eventually beat it up? If so I was going to go with a solid pin. Since I had guilt free garage time I got a set of side plates roughed out, a receiver tube turned down, profiled and threaded, and a block shaped for the inside of the trigger guard. Amazing what you can get done when you're not interupted. Here's a pic. From top to bottem. On my first build I used a grinder and belt sander to thin the parts to fit inside the trigger group. I used a milling machine to thin the block and hopefully mill the insets as one piece and not the two pieces in my first trigger group. The reciver tube is a 10-3/4" piece of 1.5"x.188" heavy walled tube turned down to 1.462" except for the area forward of the rear filler which is 1.455". I'm not quite sure of the correct length of the receiver, but it seems to work. The last .450" is threaded 20tpi. I welded two pieces of sideplate steel together and profiled the top and bottem. The top bolt is the bolt I just completed (minus the firing pin retainer), the middle bolt is the first bolt I modified, and the bottem bolt is a bolt I just got from Patjsimpson which is next in line. Since this one is definately going to be a suomi build I'll start another thread to document its construction.
 

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#216 ·
ok moleman how do you get "guilt free time" ? even my little one gived me the daddy I need call.
I do not see the problem with using a roll pin they are harden steel. if break you can easly replace. muttman
You get lucky every once in a while! I think I'll end up going with the roll pin, and if I have problems with it I'll just replace it with a solid pin. The pin doesn't even have to be in there real hard if I place the openings where the bolt is its full diameter as it would have no place to go. This one isn't taking me near as much time to get to this point as the fist one did. I'm going to see if I can cut the barrel jacket lugs into the barrel bushing so I can use the take down feature. I'll make the barrel stub 3/4" and use a larger indexing nub to prevent the use of an unmodified original barrel and avoid a SBR violation in the eyes of the atf.
 
#217 ·
Moleman thank you for the heads up on the thread, I just finished reading it. Today there was a gun show in Dayton and I was able to get my hands on a few pieces that might help me with my build. Copes has a bolt but I saw a bronze sten bolt that I would like to use but I'm afraid that I can't without having to rotate the mag to the side due to the ejector. what do you think?
 
#219 ·
well thats what I've heard but was unsure, besides I think it would look better with that bronze bolt sliding in there then the silver steel one, give it a little color. My next question is I don't have much experience with a lathe, my brother works for a tool and die company but when I asked him if he could turn down the bolt for me, he said it would be easier for him to make a bolt from scratch. So how do I make it smaller without a lathe, any ideas?
 
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