Gun build: Suomi M31 9mm submachine gun (semi-auto)

[usmcdoc14]

The next gun build by myself and others here will be the Suomi 9mm submachine gun converted to semi-automatic or whatever bastard weapon we come up with :laughing: Mine is a complete bastard gun and will post as I build it.
this is what we all start with :shaking:
http://www.pirate4x4.com/forum/attachment.php?attachmentid=236287&stc=1&d=1143336140
a cut to fuck rifle demilled by BATF guidelines.

Note the huge missing chunks in mine.
http://www.pirate4x4.com/forum/attachment.php?attachmentid=236285&stc=1&d=1143336140

Now I am building something COMPLETELY different.
I am using a severely modified Suomi bolt that is cut down and made to take a regular floating firing pin to fire from a closed bolt. It will be a blow-back weapon using either a glock or similar 9mm recoil spring and a complete FAL lower receiver for all fire control group.
This makes my life suck less because:
the bolt is now a US part(by me)
all the FAL FCG is US made
the upper is so much modified it might as well be US made :laughing:
The stock and pistol grip will be US made
i can use ANY FAL lower parts or even a FAL para folding lower.
It will not accept a Suomi full-auto bolt in any way.
It CAN NOT be converted to full-auto in any way.

Here is what it looks like as of today :evil:
http://www.pirate4x4.com/forum/attachment.php?attachmentid=236284&stc=1&d=1143336140

note how it is all fitting together.
now i would NOT recommend the method I am doing unless you are really fucking bored...really bored.
I re-pieced together the front "trunnion" area and welded it in place when it was true and the headspacing was correct. this front area can be welded together and have gaps and all sorts of shit because the barrel chamber is what sees the pressure. that and the back side of the "trunnion" is like 1/2" thick of solid fucking steel.
This is way overkill for a fucking pistol ammo :eek: They built these fuckers to last.
the barrels in theses are made to be removable. they are held in place by the barrel shield engaging on locking lugs. This allows you some freedom to work and come up with MANY ideas on how to build these.

Here is where I welded(ing)
http://www.pirate4x4.com/forum/attachment.php?attachmentid=236286&stc=1&d=1143336140
I cut off the back of the receiver tube and used another chunk of receiver tube to create the body. It is only tacked in place in the pic because I had to insure it was square.

so far it cycles and ejects correctly.
more to come as the build goes :evil:

[Hef]

You know, I was thinking of converting my TEC-9 into an SBR. I know the gun is a POS, but it's sitting in the closet doing nothing. Maybe I could turn it into something fun.

What you're talking about sounds pretty fawking cool. :D

[PTSchram]

Why are we so concerned over the parts origin? Even when I had an FFL, I never had the BATFags come and look at any of my guns to determine origin of the parts.

While I applaud the work and commitment to compliance (I am gonna build up an AK folder some day), I wonder just how necessary it is.

[usmcdoc14]

Why are we so concerned over the parts origin? Even when I had an FFL, I never had the BATFags come and look at any of my guns to determine origin of the parts.

While I applaud the work and commitment to compliance (I am gonna build up an AK folder some day), I wonder just how necessary it is.

non-sporting rifles can not be imported :rolleyes: If you have a weapon that does not consist of the required US made parts in a non-sporting rifle and it is for some odd reason checked then the weapon will be confiscated.

now seeing as I build these fuckers in my home I would also be pretty fucking much guaranteed to have my home searched and probably see some jail time :laughing:

[usmcdoc14]

Next is some pics of my bolt modifications.
I went and opened up the bottom on the bolt face as it is a solid rim retention. This will help promote better feeding and give me a little leeway if my bolt "wonders" a little out vertical alingnment.Just like an droping barrel pistol firin out of battery
http://www.pirate4x4.com/forum/attachment.php?attachmentid=236322&stc=1&d=1143347503
now a LOT of pistols fire out of battery so that does not worry me to much.(next time you fire a glock look at a few primer strike locations) mainly because it IS a blow-back weapon and the fucking chamber is .200 thick in the walls :eek: thats right. the fucking chamber walls on the barrel are almost 1/4 inch thick and then this is surrounded by the barrel locking lug/retaining thingie.
Thats a lot of metal for a pistol cartridge :laughing:
this is how the round sits now.
http://www.pirate4x4.com/forum/attachment.php?attachmentid=236323&stc=1&d=1143347503
(btw the "burnt" color on the bolt face is just the light. its not actualy scorched)

you can see how I cut the shit out of the bolt
http://www.pirate4x4.com/forum/attachment.php?attachmentid=236324&stc=1&d=1143347503
It will be cut right up to that lip when done.
The bolt has a rockwell of 69 last time I checked. I have also been told if you want to machine it to prepare for it to suck.
I am water cooling and using an abrasive cutter (translation: Mt Dew bottle and a 4.5" grinder with cut-off wheel :laughing: )

You can see the pin hole you need to knock out to get the firing pin out. This will be a bitch.
The Suomi used a fixed firing pin as it fires from an open bolt but it allows for the pin to be replaced.
The firing pin hole is STEPPED !!!!!! do not try to use a pin that fits the big hole !!!! It goes HUGE hole in the back and then BIG hole you can see inside the huge hole and then you cant see is the small hole inside the big hole.

http://www.pirate4x4.com/forum/attachment.php?attachmentid=236325&stc=1&d=1143347503
I have found that If i use a piece of drill bit shaft that fits the small ass inner hole and then use a larger punch that just fits the bigger hole it works well.
Use a hammer not a press so you can feel if its getting all buggered.

prepare to swear a few times :laughing:

[usmcdoc14]

I will most likely make a liner/sleeve for the firing pin hole and use a modified M-16 firing pin.

[Impulse Taco]

is the original gun you started out with the same thing as a burp gun?

[mike]

is the original gun you started out with the same thing as a burp gun?
you mean is it a submachine gun?

[Impulse Taco]

you mean is it a submachine gun?

No, I mean is it (the same thing as) a PPsh-41?

It looks damn close to one, but I don't know what a Sumoi is.

I was going to suggest to leave it in 7.62x25 if it was, because thats supposed to be a HOT cartridge.

[mike]

It's a Finnish submachine gun. The Soviet one, is a "copy" of this one after the winter war.

[usmcdoc14]

is the original gun you started out with the same thing as a burp gun?
same but not quite. It is a sub-machine gun in the same but the quality of machine work in the Suomi is beyond belief. They spent some serious time designing this :laughing:
your typical "burp" guns like the PPSh 41 or PPS43 were usualy of a much looser fit/quality.Or the MP-38 or MP-40 that were mostly stamped steel. Or do you mean the Sten? :laughing:

There were a few guns that were called "burp" guns :flipoff2:

[mike]

The sten's kinda fun to shoot ;)

Although the shooting from an open bolt thing was weird :laughing:

[usmcdoc14]

oh and the Suomi is a 71 round drum magazine :evil:

[usmcdoc14]

The barrel on this is like 12 inches long so I am gonna have to make it legal length. Instead of making the barrel shroud longer I will actualy extend the "barrel" itself. the OD of the barrel is .745 so what I will do is trade/beg/pay someone with a lathe to step the end of the barrel down and use some .75 OD DOM to bring the outside of the barrel to 16 inches and press/weld it into place.
The barrel extension has to be "permanent" by BATF guidelines but I will make it so I can remove it with some effort.

Or I may thread it and do the same with the DOM and then weld/blind pin it into place.

I want it to be able to fit through the bushing at the end of the barrel heat shield :D I may "port" the end. Mostly for looks as the Finnish found out that ports dont really do shit for muzzle rise with a 9mm. But it would look cool :evil:
and then later I will SBR it.

[Johann]

That is clever!

What made you look at guns as a plyable thing? Makes me realize I have a lot to learn. What ID works for the barrel extension? Just bigger than the valleys or much wider?

Was this made up of parts you had lying around the house?:p

[usmcdoc14]

That is clever!

What made you look at guns as a plyable thing? Makes me realize I have a lot to learn. What ID works for the barrel extension? Just bigger than the valleys or much wider?

Was this made up of parts you had lying around the house?:p

Guns are just another mechanical marvel to me, the same as cars , and oddly the same as the human body :D Most people fail to see that if they can build an off-road vehicle then they can build anything.

The barrel extension will just be .083" wall tubing. It can be thicker or thinner as at really serves no function other than to make the barrel longer. I want it durable and easy to install. I will turn the last .5 ish of the barrel to like a little bigger than .58 OD for a nice press fit.

[usmcdoc14]

oh and the parts were chosen by the most cheap/easy to get a hold of. :laughing:

[pepe]

What is the legality of returning a demilled gun to working condition? I would think that would be the same as manufactureing a firearm?

[usmcdoc14]

What is the legality of returning a demilled gun to working condition? I would think that would be the same as manufactureing a firearm?

as long as it fills the BATF guidelines for a non-sporting rifle with the required number of US made parts and function.
this weapon would not be able to be rebuilt as factory (unlike an AK) because:
It fires from an open bolt
it has a fixed firing pin
can not in its original layout fire in a semi-automatic setting.

once the weapon is demilled it is considered "gun parts" :D

but If I made this as a pistol then none of the rules apply

[Triaged]

What is the legality of returning a demilled gun to working condition? I would think that would be the same as manufactureing a firearm?

You live in the PRK...there is a whole'nother set of books on the laws you need to follow in order to be legal...

[animator]

Interesting ideas. I'm still several months away from a Suomi build, but it'll get done sooner or later...

AR-15 build is stepping up in front of the Suomi right now...


If you figure out a design that works and is legal, I'll use yours as a go-by :D


pic of my kit:
http://img66.imageshack.us/img66/5514/p10100517sb.jpg (http://imageshack.us)

[ZAG]

http://guns.connect.fi/gow/suomi1.html

[usmcdoc14]

The bolt on these is round and notched on the top. The bottom of the rear sight actualy extends INTO the top of the receiver.
This keeps the bolt from rotating.

I am going to use some 1/4" stock welded in and ground down after it is fitted to the slot. The rear sight will no longer be used because the FAL lower has a rear sight built in.

When I cut-rewelded the receiver tube I made sure the slot was long enough to cover the travel of the bolt.

[aloharover]

So is this just for Suomi builds or all 9mm sub guns?

[usmcdoc14]

So is this just for Suomi builds or all 9mm sub guns?

any ghetto-ass, non-factory, pistol caliber, cant buy the bitch in a store builds. that are legal :laughing:
so you bolt on 9mm AR fuckers can see your ass to another thread
:flipoff2:
unless you have a spare firing pin you want to give me and then you can post your 9mm AR in here :D

[aloharover]

any ghetto-ass, non-factory, pistol caliber, cant buy the bitch in a store builds. that are legal :laughing:
so you bolt on 9mm AR fuckers can see your ass to another thread
:flipoff2:
unless you have a spare firing pin you want to give me and then you can post your 9mm AR in here :D

I don'y consider the AR a subgun. I was refering to stens. sterlings, and mini uzis.

[usmcdoc14]

I don'y consider the AR a subgun. I was refering to stens. sterlings, and mini uzis.

yup.
why you got some other project in the works besides the Suomi's? :evil:

[aloharover]

I used .0625" and .125" O-1 tool steel and some 1/4 cold rolled.
I inserted each into the back of the bolt to measure where all of the steps are. Docs photo above shows this very well.
I cut the .0625 and .125 .45" and .35" longer then I needed respectively.
I chucked the 1/4 in the lathe, faced it, centermarked and then drilled a 1/4" deep hole with a numbered drill bit that was just under .125.
I performed the same proceedure on the piece of .125" but drilled the hole just under .0625".
I pressed all of the pieces together, heated it red hot and quenched.

[aloharover]

overall shot.
Pretty straight forward. With the press design, when the small end gets too mangled will just cut another piece of .0625 and replace it.

I have removed 4 pins so far with this. Use a store purchased punch to remove the firing pin retaining pin.

[aloharover]

Here is an extended shroud. This brings the barrel length to 16.25

[aloharover]

Final photo, this is from weaponeer.
Shows how you can use an AR fire control group in a SA Suomi build.
This involves cutting a slot in the bottom of the bolt.

[aloharover]

yup.
why you got some other project in the works besides the Suomi's? :evil:

As a matter of fact....

You wouldn't happen to have an M60 stripped trigger housing would you? Can't seem to find one for under 80$

[usmcdoc14]

Final photo, this is from weaponeer.
Shows how you can use an AR fire control group in a SA Suomi build.
This involves cutting a slot in the bottom of the bolt.

ya I saw that. If I was building a semi-auto version of the suomi as a "replica" I was going to go that route. But I Decided to build something a little diffrent. :evil:

I am also thinking about just extending the barrel shroud as it would be easy.

[mudtoy67]

Probably a dumb question but I haven't been able to figure it out....

What does it mean to "fire from an open bolt..."?


BTW I love these threads. I had no idea there was so much garage firearm construction.:smokin:

[Hef]

Probably a dumb question but I haven't been able to figure it out....

What does it mean to "fire from an open bolt..."?


BTW I love these threads. I had no idea there was so much garage firearm construction.:smokin:


It means that if your weapon isn't on the NFA registry you've got a problem.

[animator]

Probably a dumb question but I haven't been able to figure it out....

What does it mean to "fire from an open bolt..."?


BTW I love these threads. I had no idea there was so much garage firearm construction.:smokin:



Basically these terms refer to the position of the guns bolt at rest position before firing. In a closed bolt system, the bolt remains forward, sealing the breech (back of the barrel) until the gun is fired. Then it is opened, the new round feeds in, and it is ready to fire again. In an open bolt system, the bolt remains open until the time of firing, when it closes, chambering the round, firing, then it opening again for the next round to be fed.

[mudtoy67]

Thanks:)

[mudslinger99]

Here is a little info on this gun :D

Suomi (Finland)
Caliber: 9x19mm Luger/Para
Weight: 4.6 kg
Lenght: 870 mm
Barrel lenght: 314 mm
Rate of fire: 900 rounds per minute
Magazine capacity: 20, 50 or 70 rounds
Effective range: 200 meters


The Suomi ("Finland") submachine gun was developed by Finnish arms designer Aimo Lachti in 1920-1930 period and adopted by Finnish Army in 1931 as Suomi-KP Model 1931, or simply KP-31 (KP stands for Konepistooli - Automatic Pistol in Finnish language). Suomi SMG was manufactured by Finnish company Tikkakoski Oy, and licensed to Denmark, Sweden and Switzerland. Used mostly by Finnish and Sweden armies, it was also widely exported into Baltic countries, some European and South American countries. Suomi was used with great sucess during Winter War of 1940 agains Soviet Union, when, wisely used, this SMG showed to the world the importance of the submachine guns to the modern warfare. Manufacture of the Suomi was ceased in Finland in 1944, but it was used well until the 1990s, when finally rendered obsolete and replaced in Army by assault rifles.

Tecnically, the Suomi was a blowback operated, selective fire submachine gun. It fired from the open bolt, and used so called "differential locking" or "advanced primer ignition" principle, when fixed firing pin ignites the primer BEFORE the bolt stops on its way forward into the battery, so the bolt momentum of inertia is used to lock the chamber during the initial phase of shot, when pressure in the chamber is high. The bolt and receiver were machined from high quality steel and bolt was fitted to the receiver almost airtight. The rear cover of the receiver was screwed on too it also almost hermetically. This was necessary to achieve a fire rate reduction by using a simple vacuum valve in the receiver cover - when bolt moved back, the valve let the air out easily wrom the space behind the bolt. When bolt started to move forward, the valve closed itself, so difference of air pressures behind the bolt and in athmosphere slowed the bolt on its way forward into the battery.

The charging handle was somewhat similar in appearance to one found on bolt action rifles, and was located behind and below the receiver, and does not move when gun was fired. The safety - fire selector was located at the front of triggerguard, and gun could be fired in semi-auto or in full-auto
Another intersting feature was the quick-detachable barrel and barrel jacket. This feature, more adequate to machine guns, was a welcome during intensive fire-fights, when many hundreds of shots were fired in fully automatic mode.

Suomi was fed from box or drum magazines. Box magazines were conventional staggered-column ones for 20 rounds or twin-staggered-column magazines for 50 rounds each (also known as "Coffin magazines" due to their shape, these could be described as two staggered-column magazines clipped together and having common cartridge exit). Drum magazines held 70 rounds and later inspired Russians to adopt drum magazines for their PPD and PPSch SMGs. In mid-1950s Finnish army also adopted 36-round magazine, designed in sweden for M/45 Carl Gustaf SMG.

In general, the Suomi KP-31 was a highly effective, reliable and accurate gun, but too expensive to manufacture.

[usmcdoc14]

What does it mean to "fire from an open bolt..."?

or to add "in simple english" this specific weapons' firing from an open bolt: :flipoff2:

The firing pin on the Suomi's was fixed (it sticks out) and it actually set the round off BEFORE it was fully in the chamber.

here is the firing sequence to the Suomi:
bolt to rear,magazine inserted
pull trigger
bolt goes forward, picks up a round, Hits the primer and sets off the round while the round is still cambering
blow back of weapon happens ejecting spent case and returning bolt to rear.
If the trigger is held then the bolt goes forward and completes the cycle.
If the trigger is released then it catches the bolt and the sequence is stopped.

:D

The BATF does not like open bolt weapons because it is "too easy" to make them full automatic :laughing: :shaking: ummmm ya...

Open bolt weapons also require a little more attention to detail to place them in a SAFE SAFE mode.

[Overbear]

You know, you would be amazed at how similar most of the older "blowback" weapons are to modern twin tube blowback paintball markers (like the spyders, tipmans and such)....

Humm.. i wonder if, with a few changes to a harder steel, if I could adapt the trigger/grip/sear group out of a spyder into a tube based sub gun.

[hoohaa]

I hate you doc. I have a bad feeling I'm going to start building my Suomi after seeing this thread.

[SeaBass44]

..........

Open bolt weapons also require a little more attention to detail to place them in a SAFE SAFE mode.

here is my saftey:flipoff2:

[usmcdoc14]

here is my saftey:flipoff2:

35%

:laughing:

[aloharover]

here is my saftey:flipoff2:

Damn, what did you do, grind off your finger prints??

[aloharover]

You know, you would be amazed at how similar most of the older "blowback" weapons are to modern twin tube blowback paintball markers (like the spyders, tipmans and such)....

Humm.. i wonder if, with a few changes to a harder steel, if I could adapt the trigger/grip/sear group out of a spyder into a tube based sub gun.

Do the paintball guns use a hammer?

[Johann]

here is my girlfriend:flipoff2:

Fixed it for you:flipoff2:

[SeaBass44]

Damn, what did you do, grind off your finger prints??:laughing: My hands are so fucked up, I work with my hands:D
I use a finger print scanner on my computer for log in, & I'm surprised it works with my hands:laughing:

[SeaBass44]

Fixed it for you:flipoff2:

another guy with no star boggin down the bb thinking he is funny:laughing:

we should change it from no search no star to read only no star:laughing: :laughing:

[Johann]

Just couldn't resist the the set up of that pic.

No star is the only comeback ya got? :flipoff2:

Had one in the past. Will again. Red star for Chit Chat would be the most effective means of getting me off my ass:)

[SeaBass44]

Just couldn't resist the the set up of that pic.

No star is the only comeback ya got? :flipoff2:

Had one in the past. Will again. Red star for Chit Chat would be the most effective means of getting me off my ass:)
Yup, that is the best I got, wasn't it good enough:laughing: :laughing: :p :p

[jim22747]

There is another way to remove the firing pin. I have a kit that I have been working on and don't have the materials on hand to make the punch, so I decided to try to remove it Hydraulically. I found a 6" piece of 1/2" Dia. rod in my shop, turned about 4" of it to around .435" dia, to slip into the back end of the bolt with about .001" clearance, cut an O-ring groove about 1/8" back from the end. I punched out the retaining pin from the bolt and then filled it up with motor oil. Next I put the rod in the back and took the whole thing over to my press.
when I pushed the rod in with the press, there was a 'pop', and out came the firing pin, about a half inch. There was enough of the firing pin exposed to grab and pull it from the bolt body!

[aloharover]

So has anyone got their Suomi up and running yet?

[usmcdoc14]

So has anyone got their Suomi up and running yet?

my "variant" using the barrel will be test fired tomorow

[aloharover]

my "variant" using the barrel will be test fired tomorow

Doesn't count and you know it.:D

I just wonder if anyone has actually put together their 19$ Soumi yet?

I have done nothing except totally strip a couple.
I want a lathe damit

[usmcdoc14]

Doesn't count and you know it.:D

I just wonder if anyone has actually put together their 19$ Soumi yet?

I have done nothing except totally strip a couple.
I want a lathe damit

I just found I have a lathe on my compound :D and a bridgeport and a drilling machine, and a FUCKING IRON WORKER!! and a full welding shop :eek:

I am working on acquiring said resources :evil:

[aloharover]

I just found I have a lathe on my compound :D and a bridgeport and a drilling machine, and a FUCKING IRON WORKER!! and a full welding shop :eek:

I am working on acquiring said resources :evil:

Acquire as in bring home, or gain the use of?

I have a TS/SCI any chance of being able to get in and use?
I have access to a 24' truck and a full crew of movers if needed :)

[usmcdoc14]

Acquire as in bring home, or gain the use of?

I have a TS/SCI any chance of being able to get in and use?
I have access to a 24' truck and a full crew of movers if needed :)

FULL use :laughing: nothing ever "closes" there and I already have card acess.

I plan on starting small with punching some suspension tabs and shit :evil:

[Azzy2000]

my "variant" using the barrel will be test fired tomorow

Pics and/or video would be much appreciated :)

[4runner]

well, the Suomi 9mm is on the back burner, while the PPS43 7.62X25 is on the side burner stewing, and the SKS gets ready for night vision.