Now that the weld areas have been prepped and the alignment bars are made you can test fit the sections and scribe reference marks on the bars. This will show if the sections shifted during welding. You can see that the kerfs varies in width at various places and some areas will need more weld than others.

Now that the weld areas have been prepped and the alignment bars are made you can test fit the sections and scribe reference marks on the bars. This will show if the sections shifted during welding. You can see that the kerfs varies in width at various places and some areas will need more weld than others.

The next step is to modify the center section so the FA bolt and grip stick will not fit in. At this point I am only going to remove enough to keep the grip stick from locking in place. I will finish the work in this area after the grip stick mods are done.

I plan on using a 3/8" stud for a bolt block, drill and countersink a hole in the area shown in the photo. Have the recuperator installed and start with a small pilot hole, remove the recuperator and since it is thin I would recommend using a unibit on it to finish the hole. Drill the hole in the receiver and countersink it for welding.

The next step is to determine the bolt block height. Install the rails with #8 screws and slide in the bolt. measure through the recuperator hole to the flat area on the bolt. Mine measured .650" I am figuring .020 to .030 clearance for the bolt should do. you can make the pin from a drill bit or dowel.

While you have the rails in check the fit of the bolt, if it is to tight the receiver will have to be spread before welding. make a shim block to fit in the bolt groove for this.

The areas to be welded will have to be backed up with copper plate. several pieces will have to be formed to fit the contours of the receiver. as soon as I get some plate I will post photos.

After all this prep work is done I would recommend thoroughly cleaning the receiver sections. This will remove all the hardened grease and will make parkerizing easier when it is all done. I am going to boil all the parts in a citrus based degreaser. this will get all the grease out of the nooks and crannies of the parts.

I machined out the grip stick slot about 5/16" longer to prevent the fa unit from locking in. I will machine the slot to final size after the semi trigger and hammer modifications are done to the grip stick. The hole for the FA bolt block is drilled and heavily chamfered to weld in a 3/8" stud to prevent a FA bolt from being used in the gun. After this stud is in place it is time to start welding!!!

Now it is time to install the bolt block stud that prevents a FA bolt from being put into the receiver. I measured from outside the receiver to the flat on the bolt carrier. the measurement was .680", I ground down a 5/16" dowel pin to .580" for clearance and radiused the top to clear the recoil spring. I tacked the pin in place to check the clearance before welding it fully.

Now the receiver is ready to weld. I installed the feed cover to set the length of the receiver. I also checked the length against the drawing. not all dimensions match, but the cover fits, So I will work from that. The steel plates align the sections and also hold in place copper plate to back up the weld. This prevents weld filler from protruding inside the receiver. In order to reduce warping and shrinkage I welded a pass on each side of the torch cut to close the gap, then did another pass to weld the sections together. This gives good penetration and eliminates undercutting at the edge of the welds. I tacked one side, checked the alignment and tacked the other side. Then tacked the top and bottom. As you can see in the photos there are some areas that will require a lot of filler. After the sections are tacked together and you are satisfied it is straight, make some formed copper plates to fit in the bottom to back up the weld. This area can't have weld protruding inside the receiver.

Tip. Use copper to back up the area to be welded to reduce splatter and reduce impurities in the weld material.

Here are photos of the rear section welded and rough ground with the feed cover installed to check fit. The 2 holes in the bottom will need some extra attention and will be finished later. It is a good Idea to test fit the parts as you go.

When I got ready to attach the front section I found that using the rails I made wouldn't work, so I cobbled together a jig to align and hold both halves. All it is is a piece of unistrut and 4 3/8" x 3" bolts some nuts and flat washers. I bolted the rear section on and then aligned the front and bolted that tight. It made the job a piece of cake.

With the sections aligned and bolted to the jig, I removed the trunnion and welded the halves together. After welding, I rough ground the welds and fitted the trunnion.

With the trunnion installed I installed the barrel to align the front section. It didn't seem to align properly so I tacked it in place and tested the barrel for free movement and checked the over all length, it measured 37 11/16 which is supposed to be correct, so I finished welding the front section.

Now the receiver is all welded, it is time to reconstruct the ratchet plate. I have opted to do this rather than replace the whole plate as I don't have a spot welder and seems like less work. I will clean up the area , grind the welds and put in a small section from a scrap plate. This is where the BRP cut pieces are useful!

TIP. Be sure and set the receiver on the ground tripod. This will show if you have the correct length at the trunnion and will show if you are twisted or bowed.

I cut a section from a scrap section of ratchet plate, it was not the correct section so I had to cut the slot. I beveled the edges and welded it in. I also built up the slot on the bottom, I plan on using a mill to finish this.

At this point the major reconstruction process is complete. The next step will be to install the rails and test fit all the components. I am planning on using a friends mill and rivet tools this week end to make a bucking tool, install the rails, finish mill the slot for the grip stick, and possibly make some of the bolt parts. I plan on making the bucking tool from a 7/16" coupling nut and bolt, I will post pictures of it. At this point I will start on the gripstick next to get the shape of the slot to be milled into the receiver. I am planning to try to salvage the front of the gripstick to use the original attachment ears. If this doesn't work I will use angle iron for the attachment.

TIP. You can cut a replacement piece out of a scrap ratchet plate to replace the missing area. Just weld it in and clean up.

I got to use a friends lathe and mill today, I machined the slot for the buffer latch as I wanted it to fit the latch lever properly. I made the bucking tools from 2 7/16" coupling nuts and bolts. The nuts were shortened and the bottom was turned to rotate in the rails. Both bolts were dimpled for the rivet heads and one was slotted to clear the small bar in the rails. I used a pneumatic rivet gun and the setup worked good. A little more grinding and smoothing of the welds and the receiver will be complete.

Now I am ready to do the semi mods to the bolt and gripstick. I am planning on using the original mounting for the ejection dust cover, so I milled the side plates to sit flush with the receiver. By widening the slot for the dust cover pin and reshaping the pin it should work similar to the original. The first step is to determine the hole location for the trigger and hammer pins, I did this by laying the parts with the hammer cocked and made a test lock. Once I determined the holes were ok I made the side plates. The sides of the gripstick need to be cut out for clearance and the trigger needs to be place forward enough to allow the trigger spring to rest on the front of the grip stick. The hammer and disconnecter need some reshaping to work properly and to allow the hammer maximum travel. A trigger stop is also a good idea to prevent trigger slap.

Tip. The welder is set at about 3.5 on a scale of 10.

Here is a photo of the gripstick with the angle iron retainer installed and the hammer ground to clear the bolt. I still need to figure out a safety. I am not totally satisfied with this gripstick and will more than likely do another with some changes. At this point I want to finish the bolt and assemble the gun to get all the parts fitted and working. After I test fire it I will tear it down, finish grind all the welds and blast and parkerize it. But I want to see it work first.

The sear and cocking lugs must be ground off to clear the bolt block stud installed in the receiver. The feed stud will need to be drilled for the firing pin to pass through so it must be welded in place to prevent rotation. A lug must be welded on to catch the charging handle and the locking wedge must be drilled for the new firing pin.

I will be using 3/16" drill rod for the firing pin, and will drill 3/16" holes in the wedge and stud. I will take a few thousandths off the pin for clearance as the carbide drill is exactly 3/16".

After studying the anti bounce assembly I don't think that using just the spring will have any useful effect on lockup. The anti bounce assembly works like a slide hammer and without the complete assembly it won't do much. I believe that the mg 42 works similar to a browning design and fires before the recoil group is fully forward, and at rest. The gun fires while the recoil group still has some forward inertia and reduces stress on the components.

Since the gun will be fired from a closed bolt with the recoil assembly at rest the anti bounce assembly won't do anything. The bolt extensions were made from DOM steel tubing. One end has a counter bore to hold the recoil spring and the other a step to center it on the bolt.

This is the bolt locking wedge drilled for the firing pin.

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 dimensions 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 until 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 drill 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 dimensions 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 thick 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 their proper location. The DOM tubing I got for the bolt extension was a little to big on the O/D 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.

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

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, after making it I discovered that it really 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.

I am using one spring. I moved the foward 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 original one. I am going to test it tomorrow. so far this has all been guess work as no dimensions for the conversion seem to be available, I hope to clear that up when I have solid dimensions from a working gun. As for the anti-bounce spring I don't think it is relevant 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 forward, locked and at rest, I don't think you could pull the trigger fast enough to introduce bolt bounce. all this happens in milliseconds.

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 gun 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 volunteered 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 measurements of the conversion parts and post some pics and drawings, and get some quotes on getting the parts made for those of you who are interested. I need to order some parts next 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 improvements, 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 firing 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 dimensions 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.

Finally made some progress today. I tried using the 3/16" dia firing pins I made. I didn't use them because I thought they would be to heavy and they fit kind of tight. After messing around with this thing, I learned several things;


1. The firing pin needs to be the right length, if it is to long it will bind when hit by the hammer.
2. The ejector extension needs to fit properly or it will cause binding, even if it seems loose.
3. The hammer must strike the pin squarely on a flat face.


The pin design I got from some photos was overkill with the bushings, I used a couple of #8 flat washers on the 3/16" pin. all they need to do is hold the firing pin spring in the front and support the ejector extension in the rear. After welding and grinding the hammer face several times I have it popping primers consistently. the firing pin nose could protrude a little more so I plan on extending it about another .025 or so. I also ground the bottom of the bolt more to give additional clearance for the reworked hammer. I have a grip stick and new hammer coming next week to grind to the proper shape. I will head out to the range after work tomorrow to do a live fire test. If all goes well I will post pictures of the mods with dimensions of the parts.. for those of you who want to buy the conversion parts kit I will start getting prices on getting the various parts machined.

My first and easiest solution is to move the fcg back so that the hammer is forward of vertical. The theory here is that the angle of the hammer will present enough resistance to the firing pin to keep it in place after hitting the primer. This is based on the breech locking mechanism of the luger toggle lock where the pivot of the toggle is below center holding the toggle closed. Hopefully this with a stronger hammer spring will solve the problem. This also puts the trigger closer to the safety, making it easier to modify the safety to work. I have some heavier hammer springs and new hammers coming to redo this setup, hopefully it will work and save trying to design a whole new fire control group.

I got in some new AR parts today, replaced the hammer and hammer spring. The new hammer has more mass and with the new spring works well. It hits the firing pin with a nice solid thwack and makes a good dimple in the primer. I am going to try to test it Thursday or Friday night. I have some heavy duty hammer springs coming from brownells and hope to have them by Friday. I have a FAL lower coming, using the AL FCG looks promising, it should solve the primer problem with the robust hammer spring and hopefully can incorporate the FAL safety also. I am going to try to incorporate it without using side plates if possible, and will make some sort of pin on arrangement for the grip stick to attach in front.