Building The Russian PPs-43 Semi Auto
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Re-building the Upper Receiver

The upper receiver unit, or upper for short, is, in some ways, the most important part of the PPs-43. It's this portion of the gun that carries the serial number (and I encourage you to add one) and is the actual legal firearm. This is the part that is registered and controlled by Federal law. In addition, Federal law requires that the person who owns the gun (or a Class 07 Federal Firearms Licensed manufacturer) actually make/complete this receiver. As soon as you have welded this unit together, it becomes a legal receiver.

What I will be doing in this section is trimming the forward shroud and the rear cap portions of the parts kit parts and welding them onto my repair section. As is the case most of the time, careful layout and measuring is most important. One mistake here could cost me a $75 repair section and some valuable parts.

The parts needed for this process are, first, a repair section such as this Military Gun Supply unit. It has a built in blocking rail for BATF compliance. While there are several other sources for these repair sections, many of them are badly out of specs.

And second, a new trunnion and trunnion bracket. These are also MGS units. As most kits do not come with a barrel, try

I started the rebuild process at the front of the upper receiver.

First I positioned the trunnion and bracket in the upper. Make sure that the rounded tab on the trunnion fits well in the large slot in the bracket. Put the two parts together and slip them fully up inside the upper. Carefully align the trunnion and bracket in the upper with the rear edge of the bracket flush with the rear edge of the projecting tab on the upper. Please note that in this picture, I don't have the trunnion fully up into the upper yet.

I used a C-clamp to hold all of these parts in place once I got everything set. Make sure the trunnion is rotated to a level position in the upper and fits snugly in the top of the receiver. If needed, file or grind the sides on the trunnion to get it fully up in the receiver. Having the barrel in place during this gives you a nice handle to hold onto and to turn the trunnion with.

Now in the original design, there were three rivets that held the trunnion assembly in place. There were two in the front of the bracket and one in the top on the trunnion. I am not a big fan of rivets and don't do too great of a job of setting them properly. Considering the large number of original spot welds I had already run across so far, I decided to weld the trunnion assembly in.

I first tried to plug weld the bracket in using the small forward holes. Due to small hole size and weld angle, it didn't work well. Judging from the color spot on the outside of the upper, only one weld bonded to the upper. If you wish to plug weld these, first bore the front bracket holes out to 1/4" for a better weld.

For this reason, I moved to the leading edge of the bracket and welded it there.

Do not weld the rear holes! These are needed for the pivot pin.

I prepaired to cut off the rear portion of the old shroud by first placing the old part on top of the new receiver. I aligned the rivet hole in the shroud with the location of the rivet hole in the repair section. I then marked the front shroud part for cutting.

I decided to cut the old shroud so as to match with the shape of the new repair section. However, you can cut either portion. A key factor is the vent holes in the shroud. Don't cut the shroud so as to leave you with half a vent hole unless you want to cut the other half of the hole after welding.

I used a piece of 3X5 index card to act as a flexible ruler so I could carefully trace the cut-off line over the top of the shroud section.

I then used my trusty cut-off grinder to cut on these lines. I only cut down to the place where the side of the shroud started curving under, and then switched to following the contour of the curved "legs". I cut leaving plenty of metal for careful hand fitting later.

This was followed by a session of repeated cut-and-trys to get everything fitting properly.

And a good careful tack welding to hold everything in place once it fit.

I then MIG welded the seam on both sides. As you can see, a fair bit of grinding is to follow.

I had the barrel in place for tacking and welding to insure alignment.

Here is where the project was sitting at this time.

From here I moved to the rear of the upper receiver. I placed the rear section (that had the stock removed from it) on the lower and used the 3X5 index card to help decide where to cut it. I then used my die grinder to cut and square up the part.

I then returned the rear section to the lower and lined it up in the normally closed position. I then marked (on the lower) where the new welded seam (on the upper) would be.

Following this, I removed the rear section and put the front receiver section onto the lower. I installed a pin through the pivot hole in the upper and lower units for precise alignment. I then transfered the seam location mark onto the front section. I the used the trusty 3X5 index card to carry the line over the top.

I cut the front section off on this line. Everything was assembled on the lower to check fit and the to-be-welded parts were carefully aligned and tack welded. Use a straight edge to make sure that the top is level and doesn't dip or bulge at the weld.

Sorry - no picture. I was having so much fun I forgot to photograph this one!

Following the tack welds, the receiver was opened and closed to ensure that things were actually properly aligned. Due to Igor's butcher job on the front ears on my lower unit (see Lower Receiver section), I had to do some filing of the pivot holes and bending of parts to get things to open and close smoothly.

Once they were, I finished the welding inside and out.

The next thing I did was to drill the hole for the barrel retaining pin.

The Wise Lite trunnion already has the pin hole in it. I simply clamped and leveled the receiver in my drill press vise and drilled the hole all the way through.

Care must be taken in drilling the far side of the hole. By this I mean the second half of the hole after the drill bit has broken through the bottom (now facing up) wall of the trunnion. When it contacts the other side, it will be hitting a curved surface, which can deflect the bit off course. So go very slowly at the beginning and let the bit spin on the contact area a lot as you feed it in. This will help prevent the bit walking off course. Use oil to help prevent surface hardening from heat generated by the spinning bit.

I drilled all the way through the receiver too. While this leaves a somewhat unsightly hole in the top, it also allows me to get the roll pin that locks the barrel in back out if I need to. I figured a blind hole would make removal a real pain!

Well, as luck would have it - nothing lined up well. The hole in the receiver and the groove in the barrel did a poor job of lining up. So I just decided to tack weld the barrel into the trunnion at the proper time and be done with it. I seriously doubt I will ever fire enough rounds through this thing to wear out a chrome lined barrel!

Since I knew that this gun would go together and come apart a million times before it was done, I fabricated a removable receiver cross pin from some 1/4" OD X 1/8" ID steel tube. I get this from and use it for my recoil spring guide tubes for the Suomi M-31 SMG conversion. I cut it to length and tapped both ends 8-32 and used small pan head machine screws.

The BATF is rather concerned about the possibility of someone substituting an unmodified, full auto, lower unit onto a converted PPs-43 upper. Dispite the blocking rail, machined off FA bolt sear catch area and inertial firing pin, they still worry! So, when finished, I will weld this pin in place, inside where it won't show.

At this point of the game, I had already largly completed the lower unit and had the Remington 11-48 FCG installed. When I had the upper receiver attached and locking onto my lower, I discovered that the hammer was hitting the blocking rail quite solidly. I first tried grinding some off of the top of the hammer, with limited success. It got to where the actual sear notch on the hammer was hitting. I figured that this would quickly ruin the hammer. After some thinking, I decided to open a slot in the top of the receiver so the hammer would have the needed clearance.

I figured that I would need to "pay back" the amount of blocking rail removed so I decided to run a couple of beads of arc weld in front of where the original rail ended, and grind it to shape.

I knew that any alteration to this rail would require BATF approval. I called the Firearms Technical Branch and spoke to someone I knew slightly and was told it seemed like an acceptable plan, but that the final product would have to be sent in for approval (approval was granted in writing). Since I planned on that anyway, I went ahead.

The slot is 1.375 inches long and .250 inches wide. The rear edge of the slot is located 4 3/4 inches in front of the front edge of the stock release button on the rear of the receiver.

As you may note - I had already welded on the rear sight when I figured out I had all of these issues. So - I got to cut it off and do these mods. I will use the rear sight to completely cover this slot so it will not be showing.

However - This time, I will wait until the gun is totally functioning before I weld the sight on!

Since I removed some of the BATF approved blocking rail, I figured I had better put it back! So, I went in front of where the cut out portion was and used my MIG welder, on a lower setting, to rebuild the missing rail. I made about 3 passes. Following this, I used my trusty die grinder to reach down inside and contour the new rail portion to fit the bolt. Needless to say, you have to have your modified bolt in hand to do this.

Next on the agenda - cut the ejection opening and finish out the rearmost vent hole in the shroud.

One result of welding the cut off section of the shroud to the repair section is an incomplete vent hole at the junction. I used a plastic hole template I had to scribe a circle onto a layer of Dyekem layout fluid. I use this for this type of layout work. I get Dyekem from Brownell's Gunsmithing Supply.

Some work with a "rat tailed" file and I'm about done with this.

On to the ejection port.

The ejection port is supposed to be aligned with the top edge right along a line down the top/center of the receiver. The port is 2" long and 3/4" tall. The leading edge of the port is 1/8" back from the step in the bottom of the receiver, right behind the reciever pivot pin hole. I ended up having to enlarge the hole some to get reliable clearing of the spent cases.

I made a template of the port shape and located it on the receiver. I put a coat of Dykem on the receiver to aid in seeing the scribed lines. I then used a scratch awl to transfer the port shape onto the metal.

I then used my die grinder and a drill to rough out the hole.

Like this....

And then broke out the pieces using pliers and a screwdriver.

And with a bit of filing and grinding it looked like this. As I said - I also ended up enlarging it some both forward and down.

It still needs a bit of sanding and fine filing to look right.

What's left? Cosmetics and welding the sight back on.

I decided on using Lauer's DuraBake finish on this build. DuraCoat I like it because it is as tough as nails, resists any solvent or oil you will ever use, acts as a lubricant and looks good. What's not to love?

Well, the down side is it needs to be heated to 300 degrees F. in an oven for one hour. It can stink up the oven and the kitchen, so I have an old oven in the workshop for this job. Also, I have some slightly less than beautiful welds on the gun and would like to use something like Bondo to fill the pits and dips. However, Bondo melts well below 300 degrees! A little research turned up that JB Weld epoxy (avaliable even at Wal Mart) is stable up to 500 degrees once cured!

Just apply a thin coat of JB and let it cure for 24 hours in a warm place. Then sand it out, leaving only the epoxy in the dents, grooves and pits.

Before I applied the finish, I checked everything out and test fired the gun. I didn't want to ruin the finish by having to go back and re-do something.

Side note. I have stopped using DuraBake and now use standard DuraCoat. It's a lot easier, needs no baking but takes a lot longer to get really hard. I also use Bondo Glaze for filling small pits and dents. Works great and I don't have to worry about the oven heat damaging it.

I figured out that since my barrel fit tight in the trunnion, I could do a limited amount of test firing with the barrel just tapped into the receiver trunnion. Limited means one or two shots!

Once I felt it was feeding well, I welded the barrel to the trunnion. I used only one small weld and placed it in a place that would allow milling it off if I changed my mind.

You are now ready to apply the finish. Remember to use a good oven thermometer and keep the oven at 300 degrees if using DuraBake. The dial on most ovens is no where near accurate!

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