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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.
 
#150 ·
I got the remington 870 trigger group taken apart and played around with the parts until I found a good rough position for them. There isn't a whole lot of wiggle room where the sear can be positioned because of the shelf for the block that retracts the bolt. There is enough room though and here's a rough idea of where everything is going to end up. The disconnector isn't shown in the photo as it would cover up the hammer/spring positions. I may have to drop the hammer slightly in order to fit the disconnector in, but that will get worked out in the next step when I lay this out on a trigger guard mock up to test their positions. The remington hammer is shown flipped upside down, but the trigger bar is in the correct position. I did this so that I could show that I may be able to use a modified original safety to block the trigger and activate the disconnector or trigger bar. The original trigger will not work though without heavy modification and I may be better off just making a new one unless I can fit a tab to the top of it. The Remington trigger might work, but then I think it would be difficult to make the safety have a trigger block as well.
 

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#151 ·
Here's what I've come up with so far for the remington trigger setup. I found that I can use the original trigger by adding a piece to the top of it as seen colored blue. This places the trigger bar hole far enough away from the pivot point to generate enough movement to activate the sear. The other option was to drill a trigger pin lower on the trigger/housing, but that would increase the trigger pull. The blue piece at the moment is held on by one pin, but I will put two pins in the final one or silver solder it on. A benefit is that this will allow me to also use the stock trigger return spring. At the end of the longer black trigger bar is the 870 trigger bar. The stock disconector lever will need to be reworked as it would currently pass through where the sear pin is located. On an 870 TG the disconnector keeps the sear pin from being able to drift out. But since I need to save width I'll just make a new disconnector to go around the sear pin.
I will be able to use the original suomi safety by cutting off the lug seen under the hammer. The original safety detents were accomplished by a block with a punger set up in it, and groves cut into the safety bar. I have room for a smaller version of the block with the plunger as seen by the cardboard rectangle just forward of the trigger. When the safety bar is pulled back towards the trigger on "safe" it will be under the little blue leg of the piece I added to the trigger and will block the trigger. If I put a bump on the trigger bar and match it up with a bump on the safety bar I will also be able to block the trigger bar from touching the sear when placed on safe. This is even better than the remington setup as only the trigger is blocked with it. Thats where I'm at now. I still need to make a couple more refinements to the pieces I made, and make a mock up of a trigger guard to test out opitions for the spring/plunger and the disconnector. I'll also need to decide how I want to modify the trigger group so that a stock suomi trigger group won't fit in the gun when I'm finished.
 

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#152 ·
I took a break from figuring out the trigger group to weld on the front filler lug. I used a piece of heavy paper .011 thick as a spacer on the barrel jacket so that when its together the barrel jacket wont rub on the front filler. I squared it up with the barrel jacket and bolt installed and checked it with a magizine to make sure it was positioned correctly. I used a c clamp to holt it tight while I put a small bead in the center of both sides and verified the lug was in the correct position by inserting a mag and working the bolt. It fit perfectly so I removed the bolt, barrel bushing, and front filler and ran a bead on both sides, on the front, then around the back. If I had to do it again I wouldn't bother running a bead of weld on the back side as it is a pain to remove the extra weld to get the front filler on and the front filler will hide the area anyway. I still need to dress the weld down before I refinish it. Here's some pictures of this step.
 

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#153 ·
I did some more work on the trigger group today. The finished gun cannot accept an unmodified trigger group which I'm going to take care of by welding in a different lug to secure the front of the trigger group. It also shouldn't accept the full auto parts so I welded up all the pin holes except the one for the trigger. Before I'm done I will also weld in a pin to further block any "readily convertable" status. Before I welded any of the holes up I removed the block at the front of the trigger group that has the mounting lug that sticks out. Its held in by two rivets that at least on my two kits are a slightly different color than the trigger housing metal. I just used a punch to drive them out as they only had a very slight lip to them. The removed block can be seen in the third picture along with the two rivet hole locations. I then welded up the holes using a piece of copper as a backer, Then cleaned them up. In the last photo I have drilled the new hammer and sear hole. I'm still tweeking the shape of the trigger bar, but with it mocked up it does work. I'm still deciding if I want to use an ar15 type hammer spring or the coil type spring that came with the 870 trigger group. The ar15 spring would be the quick and easy way to go, but the 870 spring might give a more solid primer hit. For the mock ups I've been doing I used a spring from a drywall toggle bolt and as weak as it was it still put a dent in a dead primer of a empty case that looked only slightly shallower than what is on fired 223 brass.
 

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#154 ·
Here's a handy little jig that I used to help lay out the fire control set up. I made it out of 5 layers of plexiglass. It has helped me greatly by letting me see the componets from all angles and not just the top view. The hammer spring in the photo is the toggle bolt spring I spoke of earlier that I'm just using to help keep the hammer and sear hooked together.
 

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#156 ·
Hey! thats what my wife calls me!

Here's what I've been doing on the trigger guard. I decided to go with a coil spring setup. I made basically two blocks to hold the spring in place. The front one also acts as a hammer stop which is important as the notch in the hammer just behind the pivot hole also retains the hammer spring, so it can't go all the way foreward like it could in the remington triggerguard. It also will have the block that sticks out and locks into the rear filler. I haven't cut the locking tab into it yet and its full size in that area.
The rear most block has two slots in its long leg for the hammer to pass through. The shorter leg has a hole in it for the bottem tab of the sear which limits its movement to keep it from being able to spin around either way too far. This shorter leg also holds down the safety. I pinned the rear block in place with two pins. The upper left section of the longer leg will get trimed down about 1/4" for one of the two bars for the disconnector. I'm currently using a round plunger made from a nail, but when I remove the upper left leg I plan on using a squared off plunger to engage the disconnector and keep it centered in the basically square spring channel.
I also included some pictures of the trigger extension and the cut outs for the trigger return spring. These parts look hard to make, but actually weren't hard but took a lot of fileing time. The trigger bar is still one of the prototypes and has a nub on top for a coil spring. I want to use a heavier safety pin type spring like shown in the mock up so I don't have to move the cocking block back from fully forward. I also need to make another trigger bar as the nose of that one is not tall enough and gets caught under the notch on the sear. I also need to slightly change the angle of surface of the sear where the trigger bar pushes on it as currently its sloped too much and sometimes the trigger bar slides over it without moving the sear. This is happening because when I lengthened the trigger bar I also changed what angle its pushing on the sear from. It's fixable with either a heavier spring or just changling the two surface angles which is what I'm going to do. I'm getting down to where I wish I would of ordered the steel for the sideplates by now. I still need to also make a block for the safety detent. Thats where I'm at with the trigger group so far.
 

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#157 ·
I knew I needed to trim the hammer spring because it was too long for the shorter hole in the suomi trigger guard as compared to the remington trigger guard. The full length spring would be completely compressed just slightly after the hammer caught the sear. I cut 1 coil off and tested, then a second and tested, then a 1/2 coil, then another 1/2 for a total of 3 coil loops. The hammer has full movement and the the hammer stop spur will stop the hammer on the sear if it goes too far down. *** As a side bonus the trigger activates the sear 100% now!!! So I won't be changing the angles of the sear/triggerbar after all. I think because I was compressing the hammer spring to the max it was too much for the sear to overcome. The hammer action is much stronger than the toggle bolt spring I used in mockups. I tested the toggle bolt spring and found it was strong enough to pop a primer in an empty case even as weak as it was. I should have no problems with this hammer setup as far as primer hits. Oh crap! I still don't have the steel for the sideplates... Maybe menards or home depot has something that would work.
 
#158 ·
I only have 1 new rear filler that I'm saving for my next more proper suomi build. I wanted to see how hard it was to fix one of the torch cut rear fillers before I ordered a new one. I chose the worst condition filler I had which had heavy pitting. I cut out the torch cut area and made a block to fill it in out of 1/2" plate. Then welded it in place and cut the slot full length using the good old section as a guide. It turned out ok, but If I had to do it again I wouldn't thin the 1/2" plate to match the width of the lug on the back of the filler. I did, and I ended up a few thousands under which I had to build back up with weld. I think for the $20-$25 these cost I won't be doing this again. anyway here's a before and after.
 

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#159 ·
I cut the mounting lug on the front block of the trigger guard and its' recess in the front filler that I had rewelded. I made the block and recess slightly smaller and offset to the original lug location so that an original unmodified trigger group will not fit.
 

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#160 ·
While I wait for my sideplate steel to come in I realized I never showed how I acomplished the disconnector. I ran a dog leg back to the trigger bar just like the original remington trigger group. It works great and was simple to make out of the original suomi sideplate scraps. It pivots on the hammer pin, and acts as a spacer on that side of the hammer. I cut the upper right fork of the rear hammer spring block off to make room for the disconnector lever. The spring plunger pushes it up at the end of the hammer stroke, and the trigger bar spring pushes it back down. Here is is shown in red. Next I'll make the block that will house the safety detent plunger
 

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#161 ·
I made a safety detent today. It was pretty easy and the hardest part was welding it to the back of the rear hammer spring block. I may just make a new rear hammer spring block with the safety detent included because I wasn't happy how the weld turned out. I used a AR15 disconnector spring and a bb that I stole from my boys red rider. I'll have to get a hardened one from the hardware store next time I'm there. I installed it and worked the safety back and forth about 100 times to be assured that the bb would leave a wear mark on the top of the safety. I removed the safety and used a 3/16 diamond ball bit in the dremmel to grind a dimple at each end of the wear mark the bb left on the safety. It works great and the safety snaps into safe and fire. I'll put another pin in the nub at the end of the safety detent to relieve some of the stress on the part. With all of the parts installed in the trigger group, nothing touches the detent housing. I actually made it smaller than I thought I could. Here's some pics.
 

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#162 ·
I made a new rear hammer spring block (in blue) since I didn't like the welded one. The first photo shows the gun in the safe position with the trigger blocked by the safety. The second one shows how the disconnector (in red) moves the trigger bar off of the sear so the sear can catch the hammer again. The gap under the sear, and hole that the hook on the bottem of the sear sits in controls how far the sear can move either way. If I had a milling machine I would make the front and rear blocks one piece and mill out the hammer spring hole and hammer pivot area. But until that happens I still have a drill press, hacksaw and files. I think I've narrowed down the final shape of the trigger bar and that will be the next small part I'll make. The beat up one in the photo works but needs to have a few changes made to it for more reliable function.
 

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#163 · (Edited)
My sideplate steel came in from wicks today. I went with their .080" thick steel which is the same as the suomi sideplates on my torched receiver. I made a cardboard template by tracing the trigger guard with the stock tang attached, cutting it out and scribing its pattern on the steel plate. It took me about an hour to cut them out and fit them to the stock tang, trigger guard and rear filler. I still need to drill the rivet holes and weld them to the receiver tube. I also got the new trigger bar roughed out today and it should be done tonight or tomorrow. Here's some pictures.

EDIT: For a parts count I'm using a suomi: semi modified bolt; modified barrel; trigger, trigger housing, stock, follower, mag body, floorplate, and charging handle. That brings me up to 9 imported parts that are on the list. I am also using a suomi front and rear filler, and barrel shroud, but I don't believe they're on the parts count list. If anyone sees anything wrong with this line of thinking please let me know. I will be welding the barrel and shroud to the receiver on this build, but an original barrel wouldn't fit as I used a smaller diameter trunion and a larger indexing finger. I hope to have it ready to shoot this weekend if I get enough garage time before then.
 

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#165 ·
I think some one may be shooting a pseudo Suomi in the morning! I got the welds cleaned up to the point where the stock goes on smoothly. I rivetted in the rear filler and stock tang also. I had to add about 1/8" of weld to the top of the charging handle lug so it would grab the bolt every time. I still need to install the trigger group parts and pin/screw on the barrel for the test shoot (don't want to weld it then find out theres a problem) and general tweeking. It feeds dummy rounds fine, but I'm getting an occasional round falling off of the extractor so I'll have to figure that out yet. It may be the shape of the ejector, but I'll work on that later. Here's some pictures, what do you think?
 

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#167 ·
:thumbup1: :thumbup1:
Looks great, hoping the best and I know you'll give us a function report.
:headbang:IT"S ALIVE!!!!! I shot about 50-60 rounds through it. The first few rounds weren't semi auto, but the rest after that were. I had 2-3 jams where the case didn't fully eject, but that was about it. At 20 yards it was hitting on the left side of a 2"X2" black square, not bad for just being screwed together for a test shoot. I had used a spring from a kids toy as a temporary recoil spring until I make a two stage recoil system. I shot a box of my cast lead reloads through it with no problems. When I switched to a box of hotter fmj, the recoil spring got compressed too much and was too weak at that point. Those rounds also pushed the bolt back far enough that the hook on the top of the hammer would catch the front step of the bolt. Thats a simple fix, I'll just round that surface off of the bolt. Here's a picture of how it looks now. The 4 bolts/screws holding on the barrel bushing and barrel jacket will be replaced with welds when I'm sure I won't have to tweek it any more.
 

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#169 · (Edited)
I spent a few hours in the garage figuring out the two step recoil system. This is what I came up with. I took a 2-7/8" piece of 1/2"x.050" wall thickness steel tubing and welded a washer on one end. I cleaned up the weld on both sides of the washer and made a tight fitting plug about 1/4" long and welded that in the other end. I drilled out the plug a few thousands over the recoil guide rod and set that part aside. I Then drilled out the rear of the bolt with a 1/2" bit for about 2-3/8" before my drill bit chipped a cutting lip off and I called it a night. I'll need to get a 9/16" or 17/32" drill bit to drill the the rear of the bolt at least 3" deep for the new spring guide I made. I have a valve spring that I may use and thats what in the picture to go on the spring guide. On the base of the guide rod I'm going to put a rubber buffer to further limit travel to prevent the recoil spring from being fully compressed. It should work like this simplified explaination: the recoil spring compresses until the washer contacts the buffer; then the bolt compresses the larger heavier spring. Hopefully that should be enough to slow the bolt so that no spring is fully compressed. Here's a picture, what do you think?
 

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#170 ·
:notworthy:notworthy:nanabang:moleman, you have done it up right.I like your recoil system,I know I'll be referencing it in the future for something or another. I'll get those parts to you soon. Good job!
 
#173 ·
moleman,
just a heads up. Ill be calling on you to guide me with the firing pin removal.

muttman
Let me know what you need to know. The firing pin is in the bolt pretty tight, but not as bad as a rommy barrel pin. I'll be doing a few more here soon and will put some more pictures up. I figured out a little bit easier way to remove the firing pin, but you won't be able to use it as a firing pin bushing. I already have the steel for my second build and just need the remington trigger group.
 
#176 ·
I just ordered an extra bolt from Misty at Copes also along with some mags ect. I figure I'll convert the extra bolt to semi and sell it to offset my build cost to keep me in parts/mags whatever.
 
#177 · (Edited)
Here's some more pictures of how my 2 stage recoil spring works. The first one is about where the spring would be if the bolt were all the way forward. There is also a top view of the 870 modified suomi trigger group. The second photo shows about where the bolt needs to come back to pick up another round from the mag. The main recoil spring is as compressed as its going to get at this point as the front spring guide is resting against the rubber buffer. All further rearward bolt movement will be compressing the heavier spring. I've cut 1" off of the main recoil spring in this photo and the main recoil spring is pretty compressed. I have since cut 1" more off the main recoil spring for a total of 2". The main recoil spring doesn't look as compressed and there are gaps between the coils when the front recoil spring guide has stopped on the rubber buffer. The recoil spring can go at about 2" deeper in the unmodified suomi bolt, but you lose some of the distance when you modify it to hammer fired. I may have to cut more off of the spring, but I'm going to wait till I shoot it again before that. I ordered another main recoil spring from Copes just in case I make this one too short.
 

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#178 · (Edited)
I got out to my friends farm with 500 rounds of ammo about noon and the suomi. Unfortunatly for me I had removed too much of the weld on the recoil spring guide when I cleaned it up and the paper thin weld let go halfway throught the first mag. I had no failures to eject though and hitting the steel flipper target was extremely easy. I'll reweld it and since I'm using a large spring I won't remove very much of the weld this time.

Edit: I welded the washer back on the spring guide and left a step in it to help center the larger spring. If this doesn't work I'll just turn one down from bigger stock so that there's a lip at the back that the washer can't slip off of. While I was at it I welded in the barrel bushing in. I drilled 6 holes 3/8" wide and deep enough it was into the barrel bushing then welded the holes up. I still have the barrel Jacket to weld, but I'll only hold it on with 3 of the 3/8" welds. The barrel bushing takes the beating of the bolt stopping on it and needs to be secured better. The bolt doesn't actually touch the barrel and the barrel and jacket should be fine with 3 welds. If not I can weld the front filler to the jacket also. I'll try to shoot it again tomorrow.
 
#179 ·
I tested it again and the second weld on the recoil spring guide held up for the 50 or so rounds I got through it before the nail I had been using as a temporary plunger wore out and was no longer pushing the disconnector up reliably causing hammer follow. So I made a new plunger out of heat treatable steel. I used a briggs&stratton lawn mower valve for my plunger stock. I had to anneal it in order to turn it down and heat treat it after. Its now hard enough that a file won't cut it so it should wear well. I made the head squared off for the rectangleish hammer spring channel. This will allow full contact with the disconnector and should put less stress on that part as well. The picture also shows the heat treated trigger bar that I made out of part of the old receiver stub. It doesn't remotely serve the same funtion as the original part and so it counts as a U.S. made dart. I hope to get out later in the week and shoot it again if its not too muddy.
 

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