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fmk 3 pics?

10K views 43 replies 7 participants last post by  Rahatlakhoom 
#1 ·
I have suddenly found myself very interested in the fmk 3 and parts kits are plentiful. the recoil spring isnt behind the bolt so this would make a hammer or striker setup alot easier. BUT theres not many detailed pictures on the web. If anyone here has a parts kit I would really apreciate some close up pics of the bolt from several angles and some pics of the lower receiver from a top view and also how does the barrel nut attatch? is the receiver threaded at the front?
 
#2 ·
I was just looking at these kits.
I want to get one.
Very much an Uzi type design.
I was thinking striker fired also.
Pistol build definitely.

Just need monetary liquidity.
:smoke:
 
#3 ·
Same here. I really cant justify getting one since i just finished my uzi but i still want one just to build something. Im really suprised that not alot of people build fmk's theres literally no info on the web. but i was thinking take a page out of the uzi book and have the firing pin fixed to the striker
 
#4 ·
I found some pics of the FMK bolt.
This is a long piece.







Looks like room for a striker system. Twin spring rods perhaps that
reset each cycle. I don't know yet how much room is behind the bolt when
in battery, but I'm guessing a few inches. It's a great looking subgun and I
think it would be a fun project. Hellbox Armory has tubes for this, although
I shop around at Aircraft Spruce for 4130 tubing, less expensive.

Hellbox's tubes are fluted to resemble the original.
HellBox Armory: FMK-3
 
#5 ·
thanks! looks like it would be really easy to screw up and drill into the ejector slot while drilling for the firing pin. I agree they are cool looking kinda like a cross between a sten and an uzi. any idea what the inner diameter of the receiver is? I think reduced inner diameter would be the way to go.
 
#6 ·
That ejector slot does look excessively deep.
Might have to bore out a 1/4" hole, cut into the slot and
make a firing pin insert. File down the ejector a bit for a smaller slot.

The ID on the tube is 1.416", running about .20" wider inside the
fluted area on the left and right side.

Reduced diameter tube means turning down the bolt.
I don't like the looks of those spidery side arms running up to
the barrel recoil thingy. An option might be to install a denial pin or
block.

Again, the actual parts will give more clarity.
I see What a Country lists them for 209.00
 
#7 ·
thats why i was looking into it because whatacountry has a good deal on them. thats a good idea using a sleeve for the firing pin. It apears to me that the bolt is made of two parts the bolt and the telescoping sleeve it rides in. might be easier to drill if you took them apart. of course the best thing to do would be have someone with an EDM machine make the hole but that would probably cost a pretty penny. now the receiver flutes are no big deal to me. I would just as soon use regular tube with the right ID.
 
#8 ·
I've got a mini mill that could probably handle coring out the bolt.
The last 4130 tubing I got was 1.50" ID, so this might be close enough.
I think I will check fit first.
Firing pin may have to be fabbed to fit.
I can do this on mini lathe.
AK gas pistons make good firing pin stock.

I'm just going to have to bite the bullet and order a kit.
It's starting to look like way too much fun.
:redgrin:
 
#9 ·
I was thinking of using an ak gas piston! I have an extra one anyways. the tubing i was looking at online was 1.625'' OD 1.375 ID and 0.125 wall idk if thats too much wall thickness or not. but thats if you wanna go reduced ID instead of denial bar. I just got a milling machine for christmas and i've been wanting a project for it but i better practice with it first!
 
#10 ·
.125" wall thickness is double the normal subgun wall.
It would work fine, just heavier.

The mill sounds fun. I first got mine I practiced cutting wood
just to get a feel. I'm still a novice on a machine, but I eventually
get there.
 
#14 ·
sweet deal, Im interested in seeing pics of the lower from a top view to see how the trigger and disconnector work. I think if i build one im gonna make it a carbine and thread the barrel and use one of those ar15 6inch flash hiders and put a lil baby tack weld to make it permanently attached. Another thought i had was why not ditch the sights and put a full length picatinny rail on top of the receiver and throw a red dot on it. PS happy new year!
 
#16 ·
The FMK has a three position selector Safe, Semi, and Auto. The ribs in the tube serve a purpose of centering the bolt, reducing friction, and clearing debris in the tube. I started working on a hammer fired version but got sidetracked with the SIG repair section. A striker setup similar to the twin bar sten would also work. I was also working on a tube with the ribs pressed in. If you need anymore info just ask.
Artty
 
#17 ·
Good to see you here Artty.
It also occurred to me that a hammer or striker presents an access problem
with a fixed tube. I am thinking along the lines of a hinged tube that locks down
like a KP-44. That way you have clearance to the trigger mechanism in the lower.

Sub guns of that era were on the trail set by the M3 Grease gun stamped shell design.
Which i guess was originally a German concept cheapened for disposal and replacement.
 
#20 ·
Parts kit looks like it comes with fore and aft receiver pieces.
Blueprints aren't necessary, out of scale photos suffice.
I did this with an FBP.

The tube is pinned on to the lower like an AR but it recesses into a round backplate on the lower.
Artty

Even better than a hinged set-up.
 
#23 ·
Got FMK kit today from What a Country.
All in good shape, if not great.

FCG lower tray is nice and roomy.
Has some nice features, feels good in the hand.

Now to dream something up that works reliably.
I plan to photo document my build process once I
get going.

Nothing more fun than a bag of chopped gun parts.
:cool:
 
#25 ·
I will post some internals photos tomorrow.

I have some tubing coming from Aircraft Spruce. 1.634" I.D. .058" wall thickness
That will be close to original dia. I don't have a big enough lathe to turn down
the long bolt assembly.
 
#27 ·
6 hours later....


I had the impulse to shove an AK-74 bolt into the FMK bolt carrier.

AK-74 will readily accept 9mm round.

Here are some comparative shots.



Angle of ejector is different, but can be corrected.



Lengths are about the same, closed vs. open.



Can't you imagine a G2 Tapco FCG slamming this floating firing pin home?



I haven't done the real analysis of tolerances of how an AK FCG would work, but instinct is leading me in this direction. It could be as simple as
an AK semi-auto adaptation.

(Yeah, that is a bottle of Victory, 12% brew ale.)
 
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