Rivet build
It is best to do the build from the front back. This will ensure proper fit and placement of the parts and allow for adjustment of the mag well if needed.
Front trunnion
Insert the trunnion into the front of the receiver. It may be necessary to trim the top rails to get a proper fit. Once the trunnion is in place you will need to check the rivet hole placement. The trunnion must be flush with the front of the receiver.
Depending on the receiver used the trunnion rivet holes may need to be located and drilled. There are several ways to do this. The first option is to use a "Post-it" note. Place the note on one side of the trunnion and use a marker to show the hole location. Insert the trunnion into the receiver and lock it in place with a "C" clamp and drill the rivet holes. You can drill all the way through to do both side a the same time.
You can also make a locator jig to find the holes.
You will want to set the mag well rivets first. These are usually "Swell neck" type rivets. You can see the bevel in the trunnion that needs to be recessed for proper fit. You will need to use a taper punch to make the detent in the receiver.
Hand riveting
Insert the rivet into the receiver and through the trunnion. Lock it in place using the bucking bar and a "C" clamp. Set up the bolt cutter tool in the vise as shown and move the receiver/trunnion assembly over the jaw as shown. Apply pressure to the tool handle and the rivet will start to set. Check to be sure it crushing straight and then complete the process. Repeat the steps for the other five rivets.
Repeat for the other 4 rivets.
Press riveting
This is done using the "Plinker" style jig. Insert the rivet into the receiver and through the trunnion. Position the receiver/trunnion assembly under the ram and set the rivet by pumping the press. Repeat the steps for the other five rivets.
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Fitting the magazine
At this point you will want to fit the magazine into the receiver. Make sure that it seats all the way down. If the catch on the back of the magazine does not set flush to the bottom of the receiver you will need to file the back of the mag well to fit.
Trigger guard
Place the selector stop/spacer on the bottom of the receiver flush with back of the mag well. Be sure to locate the tab on the right side of the receiver. With the selector stop/spacer in place check the rivet holes. If you needed to file the back of the mag well it may be necessary to adjust the hole placement. This can be done with a round file. If you are using a bent blank you can lock the selector stop/spacer in place with the vise grips and use it as a drilling template.
Hand riveting
Place the receiver up side down on your work bench and position the selector stop/spacer and the trigger guard. Insert a rivet into each hole. Lower the trigger guard jig over the assembly.
If you are using a jig you bought you can turn it over and secure the receiver to the jig using some scrap wood and a "C" clamp. Set the jig over the open jaws of the bench vise and use a hammer and punch to flatten the rivets.
If you are using a jig you made per the directions listed earlier you will need to turn it over and secure it in the bench vise. Now you will secure the receiver to the jig using scrap wood and "C" clamps. You will also need to place a piece of 3/16" scrap metal under the rear rivet to hold the receiver level while setting the rivets.
Using the flat end of the punch you made start to set the rivets. Go slowly! You do not want to damage the receiver. Start with light strikes until you get a feel for how much force is needed.
Press riveting
Place the receiver up side down on your work bench and position the selector stop/spacer and the trigger guard. Insert a rivet into each hole. Lower the trigger guard jig over the assembly.
Turn it over and secure the receiver to the jig using some scrap wood and a "C" clamp. I modified this jig by welding a 1/4" bolt on each side and use a cross bar to hold the receiver firmly in place.
Align the pressing plate with the selector stop plate so all 4 rivets will crush evenly. Position the jig under the ram on the press. Set the spacer bar in place and pump the press until set. Repeat for the rear rivet.
The rivet heads should come out undamaged and there should be no gaps between the receiver and trigger guard. You will also want to insert a magazine to ensure that they will lock in place.
Rear trunnion
Inset the trunnion into the receiver. It may be necessary to trim the top rails for proper fit. This can be done with the Demel and a file. Position the trunnion in the receiver and check for proper hole alignment.
If the receiver does not have rivet holes in it you can use the old receiver stub for a template to mark the locations. Use a "C" clamp to lock the trunnion in place and drill through the same as for the front trunnion. The rear trunnion rivets are usually "Swell neck" type rivets and you will need to use a taper punch to make the detent in the receiver.
Hand riveting with the bolt cutter
First thing is to attach the trunnion to the buttstock with the screws. This will help stabilize the receiver while setting the rivets. Inset the trunnion into the receiver and install the front rivet. Lock the rivet in place with the bucking bar and a "C" clamp. Set up the bolt cutter in the bench vise as shown. Place the end of the rivet in the detent in the upper jaw and stat to compress. Check too ensure that the rivet is setting straight. Continue to compress the rivet until you have a domed head.
Hand riveting with the punch and hammer
First thing is to attach the trunnion to the buttstock with the screws. This will help stabilize the receiver while setting the rivets. Inset the trunnion into the receiver and install both rivets. Clamp the receiver to the bucking plate and your work bench. Using the end of the punch with the detent start to set the rivet. GO SLOWLY! Start with light strikes until you get a feel for how much force is needed to set the rivet and form a domed head. Complete both rivets.
Press riveting
This is done using the "Plinker" style jig from AK-Builder or the long rivet jig from Gunthings. Insert the rivet into the receiver and through the trunnion. Position the receiver/trunnion assembly under the ram and set the rivet by pumping the press. Repeat the steps for the other rivet.
Lower rails
At this point you will need to install the lower rails. The lower rails stop the bolt from rotating while it moves forward and transitions to the front trunnion. They need to be set to ensure a smooth transition from rail to trunnion. There are several ways to attach the rails to the receiver.
Rail caliber modification
The right lower rail that comes with most commercial flats is set up for the 5.45x39mm rifles. The magazines for these rifles are narrower than the ones for the 7.62x39mm cartridge. The tab on the bottom front of the right lower rail is set up to center the narrower 5.45x39mm magazine and will not allow the 7.62x39mm magazines to be properly seated.
To use this in a 7.62x39mm rifle the tab needs to be reduced by half. This can be done before installation with a grinder or after installation with the Dremel or a file.
Spot welding
With this process you will install one rail at a time. Start with the left rail. Place it inside the receiver and run the center support rivet through it from the right side. Using a 1/4" drill bit as a spacer position the top of the lower rail level with the transition ledge on the front trunnion. Lock the lower rail in place with the vise grips using a piece of scrap metal as a pad on the outside of the receiver to avoid marring the surface.
Make one spot weld at each end of the rail and remove the vise grips. make 3 more spot welds front and back spaced out evenly.
Repeat this process with the right rail adding a spot weld lower down by the hammer pin hole.
Rosette welding
To rosette weld the rails you will need to drill 1/8" holes in the receiver at the same locations where spot welds would be. Use a marker to highlight the side of the receiver and score a line 1/2" down from the top rails. You will now need to mark and drill holes through the receiver for the welds.
Once the holes are made start with the left rail. Place it inside the receiver and run the center support rivet through it from the right side. Using a 1/4" drill bit as a spacer position the top of the lower rail level with the transition ledge on the front trunnion. Lock the lower rail in place with the vise grips using a piece of scrap metal as a pad on the outside of the receiver to avoid marring the surface.
From the outside, using a MIG or TIG welder (Arc welders will usually get too hot and damage the receiver.), Fill in each hole until it is just above the level of the receiver side.
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Once it cools you can use the Dremel or a file to smooth the welds out.
Center support
The center support gives added rigidity to the receiver and stops the hammer from falling forward when field stripping the rifle. It may be necessary to trim the center support to fit.
Hand riveting
This can be done with either the Gunthings long rivet jig or the rear trunnion hand rivet plate you made. Insert the rivet from the left side of the receiver and use the flat end of the punch to form the head. GO SLOWLY! Start with light strikes until you get a feel for how much force is needed to set the rivet. The head needs to be flat so the selector will pass over it.
Press riveting
This can be done with either the Gunthings long rivet jig or AK-Builder "Plinker" style jig. Insert the rivet from the left side of the receiver and use the flat end of the punch to form the head. Position the assembly under the ram and set the rivet by pumping the press. The head needs to be flat so the selector will pass over it.
Trimming the top rails
The top rails need to be trimmed so the bolt carrier and bolt will drop in and move freely. This will entail making several cuts in the top rails and filing them down. Starting at the rear trunnion you will need to mark and cut out the bolt carrier slots. Be sure to cut these under size and file to fit!
Once you have it so the bolt carrier will fit into the slots you will need to trim the rails full length. Use the Dremel with a sanding wheel to do this. Go slowly and check the bolt carrier fit often!
When you have reduced the rails to the point that the bolt carrier can be forced by hand all the way forward finish trimming the rails with a hand file. You want to get to the point where the bolt carrier will move smoothly back and forth just by tilting the receiver.
At this point insert the bolt into the carrier and install it into the receiver as far as it will go. If necessary mark the rails on each side for the wide parts of the bolt and use a file to make cutout for the bolt to drop into. You will also check to see if the bolt will pass the ejector on the left lower rail. If it binds you will want to use a file to reduce the ejector so as not to effect the heat treating.
At this point the receiver is complete and should look like this:
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