I posted this in another forum a while back. Since then, I have test fired both, and both run 100%. The Hungarian is probably my favorite AK:
This is not intended to be a how-to guide, its just a bit of my experience, with a few tips, from doing a couple weld repairs on milled AKs. If I could stop long enough to take more pics, it might actually be a how-to
To Start:
You need a milled kit, obviously. It is best to find one that has the lightening cuts intact, as shown in the pics below. If the demil cut into these, its OK, it will just be a bit more work to make it look nice when your done. If the carrier stop on the left side has been cut, consider your receiver stub to be trash.
You will need a set of repair plates. These can be purchased, but it would not be hard to get these pumped out on a mill. I dont have one, so I had to buy mine. Look at the pics below to get an idea of what they need to look like. You will also need some sheet metal to make the receiver floor, and the lower rails.
Your parts kit may, or may not have a rear receiver stub. If you dont have one, you might be able to find one from and individual, but they are not too common. You can use extra long repair plates, and mod a stamped rear trunnion to work. If your building an underfolder, you can use the extra long plates, and just cut your holes in the sides for your locking mechanism. Your call.
This is my kit, with a T3 rear stub, and the repair plates.
Before welding anything, I would recommend you get the upper rail thickness correct first. If you have some rail left on your stub, you can use this to compare. If not, you can test fit them in the bolt carrier, as shown.
I made a simple fixture, consisting of a flat surface with a straight piece of scrap steel attached. This allows me to align the upper rail of the receiver stub with the upper rail of the repair plate.
And with an extra stub and an extra piece of repair plate to give you an idea how it works. I use this to match the angle of the receiver stub and the angle of the repair plate cut.
I weld the lower rails in place before welding the side plates to the stub. I keep them a bit long, but trim them a bit more than shown in the pic before welding the plate on.
After the angles match, clamp both pieces in place and weld.
I keep the repair plate long in the rear, then mark for the rear cut with the top cover in place.
One side welded, cover fits.
***My wife had the camera during some of the next few steps, but if your taking this kind of project on you can probably figure it out. This is just the order I do things in, for a reason***
I then weld in the left side in the same fashion as the right. Again, I put the lower rail in first, and measure for the ejector position, and cut to shape BEFORE welding the plate in.
After welding the insides and outsides, grind/ file smooth down the welds.
I use masking tape to mark the holes for the axis pins. I do all my measuring from the front of the receiver, and down from the upper rail. I use this little template to locate the safety hole. This insures that the lever will fully close the gap in the top cover when its in the safe position. Ignore the slot location on the template, I only use this to locate the main pivot hole. After the hole position is marked, I measure and duplicate on the other side of the reciever.
At this point, there is still no floor on the receiver. I find its best to get the FCG pin holes drilled first, so I can trim down the receiver wall to make sure the retaining wire will fit in the axis pin groove. The plates I have been using are way to thick in this area, and wont even allow the hammer to fit inside, much yet leave any room for the retainer. Sorry, no pics of this. Just grind down the inside walls, and recheck with the axis pin until your retention device will work. Make sure you do this BEFORE welding the floor on.
After the FCG and selector holes are done, test fit a mag against the catch on the front stub. You may need to trim down some high spots to get the mag fit right.
With the mag in place, I measure and cut the floor piece. It would almost be worth using a cut up flat for this, as you would not have to mess with the trigger hole, or the trigger guard rivet holes. Some milled guns use a selector stop, and some do not. This Hungarian does not, which is why there is a hump on the bottom of the receiver for the trigger guard to fit on. You can see this hump in the completed pics, and you can see that the Yugo below does not use this hump, as it has a smooth bottom (with selector stop).
After the floor is welded in, test fit the trigger guard with a mag in place, check for both height, and the fore-aft position. You want just a little bit of play between the mag and the catch. If its too tight, it will be a bitch to take out the mags. I welded both of my trigger guards on. On the Yugo, the TG, stop, and receiver stub were still riveted together. On the Hungarian, this was not the case, but I just did not have enough room for the rivets to fit due to the wall thickness (again, these plates are too damn thick here)
Yugo trigger guard, ready for install I notched the old receiver section that was still attached, so that it would fit inside the new receiver. Welded in from the inside. Hungarian was just welded on to the hump. I dont have any pics of that.
Assorted pics of Yugo, during build: I found it was easier to remove the barrel on this one after I knew what the lenght was going to be. The Hungarian has a threaded barrel, so it stayed in place the during the whole process.
Yugo, ready for test fire
Hungarian, almost finished.