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Suomi build

18K views 78 replies 18 participants last post by  BIG 54R 
#1 · (Edited)
Since I chronicled my first suomi-ish build that started out as a sgn-9 build I figured I'd start a new thread since build #2 is definitely going to be a suomi when I'm finished. I started with a suomi kit froms copes and 1.5"x.188" wall thickness 4130 steel tubing from wicks aircraft supply. I turned the approx 10-3/4" receiver tube down to 1.465" between centers and threaded the last .450" (the original suomi's have .4" threading) of one end 20 tpi for the end cap. I noticed that the front 2-3/8" section measured 1.455" diameter so I turned it this receiver down to that measurement. On my next one I will leave the front section full size until I weld in the barrel bushing. That way I can just turn down the welds and hide them. Next I took a cylinder hone and lightly cleaned out the receiver tube. I then took a 5" section of 1-1/4"x.250 wall tubing and cut it into a barrel bushing. The section that fits in the receiver tube needs to be 1-2 thousands over the i.d. of the receiver tube for a press fit. I copied the lug area from several different suomi receiver sections as well as using measurements from my first build for overall length. The length from where the barrel collar rests (not including the indexing nub) in the front to the back where the bolt is stopped on my first build was around 4.24" to obtain the proper headspace. I left this barrel bushing at 4.270" (with the extra length in the section that goes inside the receiver tube) so I can turn it down later to get the correct headspace. Since this is a blowback type gun it isn't as critical as a locking action, but on my first build if I let the leading edge of the bolt contact the barrel it would buckle the cases of my dummy rounds because of the short headspace. I used a max trim length 9mm dummy round as a guide and added a few thousands for good measure. This left me with 4.245" for my barrel bushing length.
The inside of the barrel bushing is around 3/4" and a suomi barrel is around .78". To keep from getting a sbr violation on my first build I: lengthened the barrel to 16-1/4"; turned the barrel shank down to 3/4"; enlarged the indexing nub to 1/4" and welded on the barrel jacket since I didn't cut the lugs into it. Even without welding on the barrel jacket there was no way an unmodified suomi barrel was going to fit in the receiver. On this build I am using the same larger indexing nub, reduced barrel shank and welded on extension to avoid a sbr violaton.
Since this is a work in progress I'll add some more pictures over the next few days to bring the build up to where I'm at. Here's a pic of my first build That I still need to put a finish on and some pics of the receiver and barrel jacket of this build.
 

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#65 ·
Thanks Kernel, the only 37mm tube I could find in the USA so far has been way too thin. Turning down a 38mm (1.496") tube won't be a biggie a I already have to turn down the 1.5" tube to 1.456ish (which is 37mm) as it is. I found some 37mmx3mm wall tubing in england, but I'd think there has to be a domestic supplier of it since several companies sell that size receiver tube.
 
#67 ·
A prexis tube is a great option for those that don't have the equipment or skills to machine the receiver. Its also a good price when you consider how much machine work is involved in making that 80% receiver. This thread is about making your own from scratch.
 
#68 ·
im pretty sure that Terry would sell you just the piece of tubing that you need so that you can still do it all yourself....

you may wanna ask him. (Hell Box Armory has taken over this part of the PRexis line of tubes)
 
#69 ·
Well I checked with 4 or 5 different suppliers that we have. No luck. The best option I can think of is getting 1.5" o.d. tubing with a 1.187-1.188 i.d. and ream it out to 1.220 i.d. if your using the original bolt o.d.

I would order and use a bore reamer like we make our gun barrels but I know most cannot do that. You could get a chucking reamer but you would have to get a 1.250 diameter reamer and take it to a tooling shop that can resharpen it down to 1.220. The reamer option I feel would give you a much nicer finish vs. using a boring tool. A boring tool can give you a real nice finish but I feel it would take longer and more messing around.

Later, Barrel Guy
 
#70 ·
Fire Control trigger group and front filler

Does anyone know if the FCG (the machined block on the front end) is suppose to fit into the front filler machined slot all the way or just locate off of it? I picked up a new front filler but the trigger group will not fit into the slot. The FCG groups is bigger than the slot on the new filler.

I'm going to change the FCG machined block size for modifing to a semi-auto etc....but I'm worried about the dimension difference depending on how the FCG is suppose to interact with the front filler slot.

Thanks, Barrel Guy
 
#71 · (Edited)
Barrel guy, the tg slot in the back of a new rear filler is undersized so it can be fitted to the gun. I recently got to check out a tnw trigger pack and they left the tg lug and rear filler slot unchanged. They added a blocking pin throught the sideplates that goes through where the top front of the trigger guard frame is so the top front corner is milled away so an unmodified one won't fit as seen here in one of my remington/suomi trigger group conversions.
 

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#72 ·
Thanks Moleman! So if I machine the slot on the rear filler and or do the trigger group housing for dimensional purposes of properly locating the trigger group. The trigger group assembly should fully engage the slot of the rear filler. Correct? I guess I'm worried about the location of the trigger group. If it is to close or to far away the I'm worried the hammer won't work properly. If to close or to far away the hammer will not swing properly and fail to hit the firing pin.

Thanks, Barrel Guy
 
#73 ·
Either machine the lug or the undersized slot in the rear filler so that the top of the trigger group rests flat against the receiver tube. I'm switching to a blocking pin like the comercial guns and not changing the slot and lug locations like I've done on previous builds. However you decide to do it, just make sure an unmodified trigger group won't fit in the receiver. What hammer setup are you using?
 
#75 ·
Moleman, the block on the trigger housing measures .393 and the new rear filler measures .380. So these should be machined so they will fit together correct?

I haven't totally settled on how or which fire control system to use. I'm weighing all my options. I've looked at your's several times. I'm also looking at what components are easily available and easiest to work with.

Right now I'm basically in some planning stages and laying everything out.
 
#76 ·
Yes, here's some pics to hopefully clear it up. You need to leave a few thousands clearance between the tg lug and rear filler slot since the trigger group is put in at an angle, then the trigger guard end is pushed down. There is a monster thread over at weaponeer on the suomi's. I've seen M1 garand and carbine, ar15's and of course remington fire control groups used as well as striker fired versions. I'm working on a limited machining remington conversion that retains the original suomi front trigger group lug.
The top pic shows how the stock tang, trigger group and rear filler fit together. The bottem picture shows a new rear filler and one that I've rewelded and relocated the slot on.
 

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#79 ·
I was thinking of getting a suomi kit from CFS but figured the reweld would be 2 expensive for me at the moment since I have several unfinished projects so I said no...

After 'suomi envy' I think I will probably get a kit and store it with the rest of my 'guncrap' as the wife calls it and wait for a rainy year or 2 down the road!:kick:
 
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