First before you begin there are a couple of modifications that must be done to the receiver BEFORE you start welding it to make it legal. The gripstick area must be machined out to not accept an unmodified full auto grip stick. Second the receiver must be modified so that a full auto bolt will not fit in. This is done by welding in a block or stud in the rear of the receiver.

Modifying and Welding the Receiver.

I have had my kit for several days and have been figuring out how I am going to get the receiver welded up properly. While the kit contains all the parts for a complete gun, I do not think that it is a parts set from one gun, hopefully this will not matter.

I am planning on starting from the rear of the gun and working my way forward.

The first step is to grind all the cuts and remove ALL the slag and burned metal to get to a clean solid surface. I would recommend blasting the weld areas before welding. I plan on TIG welding it and the rule for TIG is the cleaner the better.

I made a set of plates from 1" x 1/8" and 1 1/4" x 1/8" steel to use as a guide in clamping and locating the parts for welding. These are nothing fancy, set them inside the receiver along the bottom and drill a few holes through the rivet holes to hold them in with #8 screws.   These will aid in the alignment and setting the length. The bottom photos show them in place.

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!!!

Fig 9 This is the hole for the bolt block stud.

Fig 10  This is the gripstick slot extended to prevent a FA unit from being installed.

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.

Fig 11  View of bolt block stud inside receiver.  Note steel bars holding receiver sections aligned. 

Fig 12  Bolt block stud tacked in place.

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.

Fig 13  Completed weld ready for grinding.

Fig 14  Top of receiver.

Fig 15  Bottom of receiver.

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.

Fig 18  Bottom rear, 2 holes that need to be reconstructed.                                            

Feed cover test fit.

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.

Fig 20  Gun on jig.

Fig 21  Gun on jig.

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.

Fig 23   Sections welded and trunnion fitted.

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.

Fig 24  Front section aligned and tacked in place.

Fig 25  Front section finish welded.

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!

Fig 26  Ratchet plate to be reconstructed.

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.

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.

Modifying the Gripstick.

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.

Fig 34  Semi complete gripstick.

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.

Modifying the Bolt.

Since the gun will be fired from a closed bolt with the recoil assy at rest the anti bounce assy 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.

Fig 39  Bolt extension sleeve.

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.

Pirate                    

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