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How Hard are Suomi M31 Builds???

20K views 78 replies 41 participants last post by  rocco1911 
#1 ·
#3 ·
AFAIK, there have been no parts kits builds to date.

What we need is a blank for the receiver housing, and a trunion. The trunions on these are torch-cut thanks to the ATF. All other parts appear usable.

I have no idea if anyone is making a receiver cover or trunion. The receiver cover will need to be a bent sheet metal ordeal (probably 16-gauge 4130). Someone like coldsteel will have to give us one of those.

The trunion MAY be a millable part. There's enough damage to it that it is hard to get a good idea of the measurements.

Of course, making it fire semi-auto will be interesting. Along with US parts. Not even sure of the parts count on this. Since the stocks are all wood, maybe ironwood or someone can make some up. Wouldn't need to be fancy... they "look" mass produced if you know what I mean. Then again, it would be SWEET to get a re-worked wood stock that just LOOKED nice - built from the ground up as a looker.
 
#4 ·
Well let me take a step back.

The Semi Suomi build will be as hard as a Semi Sten build. The Suomi is a classic bullet hose, and therefore there's no real parts to switch. There's not even a removeable firing pin! The firing pin is practically a part of the bolt.

I'm thinking you could adapt parts to build into a classic AK style FCG, and mill into the bolt for hammer clearance to strike the firing pin you would need to add. Heck you could probably mill a G2 FCG thin enough to work, then adapt the trigger housing to accomodate these parts. But it would be just as hard to do it with brand-new parts fabricated from 3/16" or 1/4" bar stock from HD.

Also, the receiver housing is more destroyed than I thought. You could clean it up, but it will need mucho TLC and I don't think most people will be willing to provide that. You could probably get by with the sten tube route, by taking some gas pipe or other suitable material and cutting it up real good. The magazine well may be salvageable after some clean up with a dremel sanding disk. The trunion area would still need to be fabricated.

Let's not forget the US-made parts that will be needed. Don't even know the parts count but < 10 foreign will be needed. AND a barrel extension will be needed. The existing one could be lengthened. Only talking about 4 more inches or so.

It *could* be done but it won't be an afternoon project. You'll need a mill. You could do it with a dremel, tons of cut-off disks, and patience. Lots of patience and TLC. I predict it is too big a project for the casual builder - there are easier things to build.
 
#5 ·
Thanks hcpookie. I didn't even realize that is was full-auto. I was taken by the $50 price so a person wouldn't be out much in case they completely screwed up the build.
 
#6 ·
Hello guy's

I don't own a Suomi kit yet, but I would be interested in making this receiver housing and the Trunnion. I will let you know what I come up with.
I am making the Ppsh41 full lenght blank, it will come with under size vent holes, a barrel support and a end cap to be drilled.
I plan to have available the barrel trunnion by the first week of Feb.
 
#7 ·
The real obstacle here is that these weapons fire from an open bolt. To convert to a closed bolt configuration and adding the necessary FCG internals make these a pretty tough cookie. Just like a Sten, new internals would be required (or severely modified).

Not sure offhand about the US parts rule applicability. How many BATFE listed "evil" parts do these have? All I see is a removeable hicap magazine. No pistol grip. No flash hider. No bayonet lug. No grenade launcher. If they don't have 2 evil parts than the assault weapon classification (no more than 10 foreign made parts) rule shouldn't apply. Someone correct me if my memory has slipped.
 
#8 ·
RetVet said:
The real obstacle here is that these weapons fire from an open bolt. To convert to a closed bolt configuration and adding the necessary FCG internals make these a pretty tough cookie. Just like a Sten, new internals would be required (or severely modified).

Not sure offhand about the US parts rule applicability. How many BATFE listed "evil" parts do these have? All I see is a removeable hicap magazine. No pistol grip. No flash hider. No bayonet lug. No grenade launcher. If they don't have 2 evil parts than the assault weapon classification (no more than 10 foreign made parts) rule shouldn't apply. Someone correct me if my memory has slipped.
Bayo lug / grenade launcher / yadda yada - all those features fall under the AWB that is now sunset and moot. The *ONLY* issues here are:

1. Parts Count (crime bill)
2. Open Bolt vs. Closed Bolt (need closed)
3. Barrel length (16" min)
4. Overall length (should be covered w/ #3)

yes, will be "fun" to say the least. Machining is required and will be almost the same as a semi-auto sten build.

hth,
- Jerry
 
#13 ·
Cephus said:
I was kinda thinking that the mag well and the barrel would be good for a 9mm AK conversion and the drum mag looks cool too.
You'd think it, wouldn't ya? So did I...

Mag well area is toast, as is the trunion. Totally destroyed according to ATF. Thank you, banana bunch!

The barrel will work however it is 12" long. It is super thick - nearly 1" in diameter. Presumably this was to allow the bullet hose to accept a ridiculous amount of heat. The barrel on mine looks good, although you can tell it has been through the ringer.

Unlike an Uzi, the breech of the barrel has two things that may require some work... 1) A notch for the extractor, and 2) a recessed area for the bullet guide.

The mating surface on the barrel breech doesn't support a bullet like an Uzi so there may be some trial-and-effort to get the breech to work correctly w/ an AK-74 bolt. In other words, if you cut the breech down to remove the extractor notch, you would have to ream the chamber again. Not sure if it is worth it, considering the $20 Mini Uzi barrels at CDNN.

I have it and plan to play with it some. I'd like to lighten the barrel - it is a bugger! My 7x10 lathe (technically a 7x8 lathe) SUCKS and I can't cut it all at once. SO... I'm seriously considering buying the 7x14" lathe bed from LMS so I can work with the barrel. I hate to do it, but it would be better than nothing.
 
#16 ·
NO, not really. I was using the AK FCG as an example of a ready-made source of US parts that fire closed-bolt. I would build based loosely on the AK only because I'm familiar with those parts. I haven't even taken the trigger housing apart yet. Since the trigger assembly is build for FA open bolt design, it needs to be tweaked to work only for closed bolt semi. Who knows, it may work with a bit of dremel work...
 
#21 ·
I have my kit, but I am in no hurry to build it.

Just the idea of a semi-auto rifle that takes a 72-rd drum is pleasing to me. Plus, I already have the drums and magazines on hand.

When I finally get around to building a SA Soumi rifle, I'm ready. Heck, I even have the metal lathe to make the barrel bushing.

One way to determine the length of the barrel bushing is to insert a magazine within the housing, and measure the total length of the bushing resulting there from. I hope that makes sense to y'all, it does to me.

It appears that an M-1 Carbine FCG "might" work in the SA version. If so, the trigger housing can be modified as well, resulting in (4) U.S. made parts. The receiver will be the "magic" 5th U.S. part.

The bolt will have to be modified to match the FCG. The length and weight of the bolt can be reduced. The bolt was designed for full-auto fire. A semi-auto bolt will not require as much weight.
 
#23 ·
The Suomi is an interesting problem. Is the thing even modifiable
to a closed bolt? I'm asking, I have no idea.
I like the M1 Carbine FCG idea.

I'd like to see it happen, but need to know the theory behind closed bolt
operation first, I'm going into this blind.
Any ideas?
 
#24 ·
It would be a challenging project to convert the Suomi to a semi auto rifle. IMI redesigned the Uzi for semi auto only when they imported the Uzi for civilian use. They used a closed bolt and almost made it impossible to convert the Uzi to shoot full auto. Maybe if Prexis will make a semi auto only receiver for the Suomi along with a closed bolt with a moving firing pin, then we could build a nice plinker out of it.
 
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