Fun with the MP-44 bolt/it's done

[trenches]

This has been a real learning experience. I started with a section of 8620 alloy. Used the specs of the drawings I have. got close. The main problems is the hooks on top and the groove for the ejector. So I milled off the hooks and made a new piece. Dovetailed it in. And made the ejector groove a bit deeper and higher.
I also found something that was not on the drawing. The rear of the bolt has to be a smaller diameter than the front. If not then the bolt will not drop down to lock up. Found that out the hard way. So I reduced the diameter of the rear end. I made the new hooks according to the drawing. Or so I thought.
The problem is that the height of the bolt has to fit into the window of the inside top of the receiver and the top of the trunnion. Also found that out the hard way. Once I had that corrected I slid the bolt and carrier into the receiver.
Well it wouldn't drop down. The carrier has to cam the bolt down by using that ramp on the bolt and carrier. So I gradually reduced the height of the hooks. After a lot of futzting around ( that's a Pa. Dutch term) I finally got the bolt to lock down. Then I had another problem. I need to add a bit of metal to the bottom of the hooks. As the bolt goes back those hooks on the carrier engage the hooks on the bolt to lift the bolt up out of lock up.
But now I have the carrier and bolt sliding in and locking up. And when in battery the bolt doesn't lift up. When the mag is in place it puts pressure on the bottom of the bolt. Found that out the hard way too.
Now if you put the bolt and carrier in the receiver and tilt the front of it down, the unit slides down and locks into battery. Happy Days.
I ran an aluminum rod down the muzzle to see if I could push the bolt back. Nope. But if you really jerk on the charging handle the whole unit comes back.
Also when locked down without the return spring in there is no back paly in the bolt. I'm tight up against the locking shoulder.
I had tried to remove the ejector for a test. No dice. That thing is in there.
So for now, I'm going to add a bit of metal to the bottom of the hooks. They won't look so skinny then. Then I weld the hooks to the bolt. And then fit until everything is fine.
Then I finish with the extractor and firing pin. I'm going to use this bolt as test bolt. Once everything works as it should then I'll make new bolt using this one as a pattern.
So here it is so far as it is made. In the one picture you can see one of my oops! moments at the ejector port. My measuring foo was off slightly. BTW those 2 little holes are for the ejector pins that I took out. I have to put them back in.
Oops the first pic is a bit fuzzy. But the bolt is locked down and in battery. Also I know that the carrier is up against the bolt. The back of the anvil in the carrier sticks out and won't go forward. Which tells me that the carrier is up against the rear of the bolt.

 

[biggymu]

Here’s a view of my MP43. It shows the carrier holding the rear of the bolt down in the locked position. This would also resist the upward force of the magazine. Following along with your trial and error method of making this work, quite a bit is going on with this deceptively simple locking device. I enjoy reading your progress.

 

[trenches]

Thank you. It's not as simple as we would believe. I'm going to make new hook piece now that I am very close to finish. I now have the measurements I need.
Yep, there is a lot of things going on as that bolt and carrier go forward.
Looking at your picture I will have to make the ejection port larger too. And if you look closely you can see how the back end of the bolt is down at an angle.

 

[trenches]

Think I got it. Made a new hook part today. It works. Locks and unlocks. I made the hooks thicker and now when the charging handle is pulled back it unlocks pretty good. Before it was very difficult to unlock. The hooks were not wide enough. Took care of that. And the mag doesn't push the bolt up either.
I'm thinking of making that triangular firing pin. And using the spring that powers the extractor to bear on the pin. Not exactly like the original but close to it.
Still some more work to be done on the bolt yet.
But I have the main part done. What a struggle at times.

 

[mnguy62]

I really admire your skill and patience. I have neither! Wish I did.

 

[trenches]

Thanks. Skill is learned by trying. I'm a carpenter, cabinet maker, and sheet metalworker by trade. I'm what you call a self taught machinist. With lots more to learn.
One of the hardest things I have done is make a Chauchat bolt and carrier. Had to make the helical grooves in the carrier and studs to match on the bolt.
I've been contemplating building an FG-42. But in 7.62x54R using Lahti 20 round mags. Might figure out how to use an M-60 bolt in a Mosin front receiver section and using a Mosin barrel. Then again, I just might make the trunnion. I have the book "Death from Above". Scaled parts from the drawings in it. Thinking of making the receiver in 2 halves and welding them together. Unfortunately Dingo has decided not to import the flats so my only option is to make a receiver.
Yeah, I know I'm not right. LOL.

 

[trenches]

The extractor and firing pin are made. And the extractor works. With the spring in it holds the cartridge tight against the bolt face. You can shake the bolt and the cartridge stays in place. What I did was steal an idea from the Germans. After I made the firing pin I drilled a hole in the extractor mortise. I have a flat spot on the pin. With the extractor installed the spring bears against the firing pin. Keeps it in place.
The pin uses a piece of drill bit for the tip. It is loctited in place. Easy to replace if it gets broken.
Tomorrow I'll weld the hooks to the bolt. I'm using 3.5% nickel rod. The stuff you use to weld on bolt handles to bolts. Good stuff.
And after that it is only a matter of refining the bolt a bit.
And that piece of headache will be over and done.
And then the next headache starts. The grip stick.

 

[trenches]

The bolt is done. It works perfectly. Except for one thing. The extractor won't ride over the rim of the cartridge. Not sure what is going on. I made the front like the drawing. I'm thinking it may be the timing of the firing pin. Have to do some experimenting with the firing pin out.
I didn't make that scallop on the right side as deep and wide as it should be. No matter. There won't be a port cover for awhile.
But it's done. I'll get the extractor problem figured out.
And rounds feed from the mag real good. That's a plus. They go out of the mag and right into the chamber.
In the first picture, you can see that the bolt hooks are wider. The hooks on the carrier pull up the bolt as they should.
And now I have a good pattern to make a new bolt. Once I get the extractor problem fixed. But this one should work ok until that time.

 

[trenches]

I now have the extractor working. Took one coil off of the spring and put more of a bevel on the front. It will now strip a round from the mag, chamber it, and extract it. Still needs a little improvement but it works. Works great with the return spring in also.
Now onto the grip stick. And a little more polishing of the bolt.

 

[biggymu]

Wow you fixed it before I could even post. Looking at my bolt (and it could simply be the angle of the photo) it looks like the extractor pin is too far forward which may produce a difference in leverage.

 

[trenches]

That's a possibility. I can always drill a new hole. I think you are correct about the leverage. I forgot to look at the drawing when I was getting ready to drill the hole. Sometimes I do get ahead of myself. Easy fix though. And I can make a new extractor in any case. Still have lots of 4140.
But considering that I only had a very rough original in my hands for a short time and that I had to work off of drawings and convert from metric to English I don't think I did too bad. I don't really trust the metric/ English calipers too much. I most often use my standard calipers or my Starrett mike. I have a pin gauge that I use to double check the calipers.
And a lot of eyeballing.

 

[biggymu]

Your ability and tenacity are admirable! Can’t wait for the finished product!

 

[trenches]

Thanks. Tomorrow I may start on making the grip stick. I have plan to make the ribs on it. Should be fun. Once that is made the rest is a piece of cake.
First though I have to make a template to make sure that the locations of fcg parts are in the correct positions.