www.MG42.us

Moving ahead slowly, Getting near the end and ran into some clearance problems. Since I
have been working off photos from the site with no dimentions it has all been guess work.
I ran into problems with the stud for the cocking lever on the bolt. I welded it in what
appeared to be the right spot, and cut the cocking lever, I installed the bolt and all looked
good untill I tried to install the bolt with the recuperator in place. The stud hit the side of the
recuperator and wouldn't go in the gun. I ground the stud for clearance and got it in. Now it is
a little narrow and I will have to make another one and relocate it closer to the center of the bolt.
I ran into another clearance problem with the bolt extension sleeve, it is about .025 to large in
diameter and needed some clearance ground off on the bottom.
The hammer needed some major grinding as did the disconnector. The bottom of the bolt was
ramped to ease it's travel over the hammer. The next step will be to determine the length of
the mainspring. I plan on getting some good measurements of the total length compressed
and the total amount of space available for the spring. Hopefully I will get it right the first time.
All that is left to do is drll the hole in the feed stud for the firing pin and make a firing pin, then
I can start final assembly / fitting of all the parts to do some test firing.
I will post some dimentions of some of the parts for reference as soon as I have it all together
and working.

Got to use my friends lathe and mill today and made some firing pins and a bushing to
drill the feed stud in the bolt. The bushing centers the drill bit and with a carbide bit and
some tap magic it was an easy 5 minute job. I made 2 sizes and styles of firing pins.
the first were made from .187 drill rod, one has a pin tip machined and the other has
been drilled to take a section of the german pin. The .187 pins will have to be polished
down as the fit to tight in the 3/16" holes. The second set are .156 and fit loose.
I would prefer to use a heavier pin. after I determine the proper length I will harden
and temper the ends. I made some thich bushings to hold the pin and ejector extension
from cold rolled steel. I will either silver solder or weld them on as soon as I determine
thier proper location.
The DOM tubing I got for the bolt extension was a little to big on the od so I milled some
clearance slots in it to clear the recuperator. I am ready to weld it on and determine the
firing pin length.
after that is done the next step will be to tear down the gun, clean and lube all the parts
and reassemble it for feed function and if all goes well test firing.

At this point I would like to give a few words of encouragment to those of you with a kit.
This looks like an impossible task, but it is a very doable build with a minimun of equipment.
It just takes some time and ingenuity. once I have this working and finalized the dimentions
for the parts I may offer a set of parts and materials you need to finish your kit. I wil start
a thread for this in the for sale section.

Pirate wrote: I made 2 sizes and styles of firing pins.
the first were made from .187 drill rod, one has a pin tip machined and the other has
been drilled to take a section of the german pin. The .187 pins will have to be polished
down as the fit to tight in the 3/16"

MSC direct has some 0-1 drill rod in .185 dia for about $2 for 3'. i ordered some today. This should be just about perfect for the .187 hole

Where did all the pictures go?

I don't know, I pm'ed Salt to see what happende to them. they are still on my tutorial in the faq section

There was a problem with the pictures?


:P



Steve

Finally got started again today after a grueling week and a half on the road. I ordered an
electric die grinder from HF and finally got it yesterday after waiting 2 weeks and it didn't
work, so I had to piss away a half a day to return it for one that works. They had 12 ton
presses on sale and got one of those also.
The plan was to finish the bolt mods and do a final fit on all the parts and lube it up to test fire.
After welding on the bolt extension I had problems with the bolt binding, after resolving that problem
I spent some time making a ramp block to go around the bolt block pin, agter making it I discovered
that it reeally wasn't needed.
I welded the bushings on to one of the firing pins I had made a few weeks ago and when checking
it for brittleness snapped it off at the welds. I got some silver solder and will solder up a couple test
pins tomorrow.
All in all not much progress was made today, ,hopefully tomorrow will be more productive.

Pirate...
Sorry bout that grinder.
I wanted to ask you your thoughts on where You're placing those bushings on the firing pin.
Here's why I ask...
Since The firing pin must reach full protrusion in the bolt face for the primer, the
front bushing placement is directly related to the type of spring you intend to use.
Same with the rear bushing and spring, as I found that the bolt carrier (rear portion)
has one last forward move ment when the wedge opens the rollers...and without enough
front spring tension..and too much spring on the rear...it will push the pin forward and fire the round
So the front and rear spring must hold the pin in a Neutral position on forward movement, and the Hammer
still collapse the front spring.
I started thinking about anti bolt bounce's again, and how that could 'relieve' the pin from the duty of resisting
the carriers last forward thrust. Or, a firing pin made of all thread....front and rear smoothed out, and adjustable
bushings. It would make a great prototype.

I am using one spring. I located the fwd bushing back enough for the spring I am using.
the back bushing is a guess. The firing pin stops on the bolt, it has a shoulder, I turned
the pins to match the origonal one. I am going to test it tomorrow. so far this has all
been guess work as no dimentions for the conversion seem to be available, I hope to
clear that up when I have solid dimentions from a working gun.
As for the anti-bounce spring I don't think it is relavent to a semi auto closed bolt gun.
I am guessing but I would say it would work like a browning. when the recoil group
moves forward the gun fires a split second before the recoil group is in full battery.
this absorbs some of the forward momentum and keeps the recoil group from hammering
into the receiver. Since the FA 42 operates at a very high cyclic rate the bolt bounce
feature is needed. during a fa firing cycle the bolt slams shut before the recoil group
is all the way home, when it hits the bbl extension the slide hammer action of the anti
bounce mechanism takes over and pushes the bolt lock fwd and holds it.
In sa operation the recoil group is fully foward, locked and at rest, I don't think you could pull
the trigger fast enough to introduce bolt bounce. all this happens in miliseconds.

What I'm describing is not bolt bounce....which the term is focused on the bolt Face
actually pinging back some before detonation.
Since this is semi.... I guess New Terms should be used.
How about "carrier bounce"....were the rear portion of the bolt has enough
force from buffer spring/ and its own weight-to Compress the Front Firing pin spring
If your Bushing is right on the Feed stud in the back...then it might go full
when you let the cocking arm go. Maybe try single rounds 1st to see if you can
get the round off by releasing the Cock arm on it. Should be interesting.
Take your camera, and pictures of the people asking you WTF you're shooting....you
crazy pirate

I kept the rear bushing away from the feed stud. I wanted it to be fully floating., I also
tried to keep the weight to a minimum to reduce the chance of unwanted firing.

I got the gunn together today, the silver solder didn't work, I used some regular solder
and it seems to hold the bushings in place. I will get some silver braze next week, I
didn't want to waste a day getting it. After lubing the internals it works a lot smoother
but still seems tight. hopefully a few dozen rounds through it will loosen it up and show
where it is to tight. It feeds and ejects so hopefully it will function with ammo. I will
be going to the range tomorrow, I voulintered to help clean the place up as it got
trashed from the storm. I will take some photos.
If the gun works I can get measurments of the conversion parts and post some
pics & drawings, and get some quotes on getting the parts made for those of you
who are interested.
I need to order some partsnext week, I want to do another grip stick as I don't like
the way this looks or works. I need to get another retracting handle spring too as the
one I had is broken.
As I see it right now there are a few areas that need improvemrnt, one is the retracting
handle it needs a hold open device and away to keep it from jumping over the bolt
retracting stud. The front attachment for the grip stick could be better and a working safety
needs to be incorporated. Once I know the gun works I will start on these improvements.

I have spent a few hours trying to figure out why the gun won't fire. The firing pin seems
loose enough and I don't see anything binding. I have tried to fire it without the ejector
bar and without the firoing pin spring. no luck, all I get is a tiny dimple on the primer.
Karbinator and Abwher have been kind enough to post some photos and dimentions and
hopefully this will help me solve the problems. I see that brp uses a thin firing pin, so I
guess I will abandon the idea of using a 3/16" pin. I have ordered some parts and hopefully
will be able to use my friends lathe this weekend to make some test parts.
I got a g3 kit and am looking into seeing if the fcg will work. the push spring type hammer
is better than the ar type. I have another grip stick on the way and have some ideas about
a better way to attach it in the front.

Seeing as how you already have a G3 kit Pirate this might be irrelevant for you. But what about using a CETME FCG for people on a budget? Maybe use the cheap Century semi-auto parts that they've made for their CETMEs and G3s... (Are there any differences in the G3 and CETME FCGs?)

Just thought I would throw that out there..... Any input on that?

Matt, I am not sure of the differences,I am not a g3 or cetme expert. however at this point I don't think it will work.
The hammer sits a lot higher and the trigger is to long. There are other options, sks, m1
carbine to name 2. I am sure when all the brains here get going we will have a better
replacement!!

Pirate,

I really like 3/16 od
The hammer may bend anything thinner
I'm sure your feedstud is welded on the bottom of the carrier,
if it can turn at all, it will bind the back of the pin when the hammer hits.
You didn't say what kind of ejector bar you're using, nor can I tell
where you placed those bushings on the pin, but I do remember having
an intital problem with the Mg3 eject.bar (short non wraparound type)
it would get caught on the front end of the Rear bushing, as you can
imagine, it not only kept the piring pin from entering the bolt face, but
after two or three re-cocks to clear whatever was causing the prob(couldn't
see, just clearing the round) it would bend, or completely break the rear
bushing off the F pin! However, I see you ssaid you tried a shot w/out Bar
installed...

cetme and g3 fcg are 2 totally different animals


what about the AK FCG?? super cheap and this one has a great trigger pull

http://www.tapco.com/product_informatio ... 1&back=yes

Pirate wrote:I have spent a few hours trying to figure out why the gun won't fire. The firing pin seems
loose enough and I don't see anything binding. I have tried to fire it without the ejector
bar and without the firoing pin spring. no luck, all I get is a tiny dimple on the primer.
Karbinator and Abwher have been kind enough to post some photos and dimentions and
hopefully this will help me solve the problems. I see that brp uses a thin firing pin, so I
guess I will abandon the idea of using a 3/16" pin. I have ordered some parts and hopefully
will be able to use my friends lathe this weekend to make some test parts.
I got a g3 kit and am looking into seeing if the fcg will work. the push spring type hammer
is better than the ar type. I have another grip stick on the way and have some ideas about
a better way to attach it in the front.

pirate this dimple thing is a reocurin problem with mine also, even tried w/o fp spring and made the pin so it protruds enough to blow through the primer and no luck????

Make sure the pin does not protrude too far out behind the feedstud
You hammer will only mash the bottom of the pin, or bend/jam.
I put a picture on another thread a few days back w/measurement
It was hit or miss on my primers till I ground some off the back, I think
there's less than an inch from the straight edge of the ejection collet to the
end of f pin.