This is the second part of my post on building an AK74.
Please note that I am not a gun smith, engineer, or machinist. These tips and thoughts are based on my own experience and are for educational use only. You should obtain proper instruction and training before attempting to use any tools or assembling a firearm. If you decide to use or apply these tips and thoughts, you do so at your own risk.
Threading the Trunnions
To do the screw build, you will obviously have to thread the holes in the front and rear trunnions. Remember, use plenty of oil and go slow and easy, backing the tap out often and cleaning and oiling it. I wasn't so careful on the first hole, and ended up breaking off the tap (which was a major task to get out).
Remember that on the back most hole on the rear trunnion, you will actually be threading it to accept a screw from both ends. It's easier to tap from both sides rather than try to run the tap all of the way through.
Prepping the Receiver
Check to make sure that the rivet holes in the receiver are big enough for you to slide the screws through. You don't want the screws threads to catch on the sheet metal of the receiver; instead, you want the screws to pull the metal wall of the receiver tight against the trunnions. The metal for the Nodak receivers have been heat treated, and they will strip the threads off the screws if the holes are not big enough. A quick pass or two with the 1/8 inch cutter should be sufficient to open up the rivet holes.
Seating the Barrel
As I stated above, the hole in the front trunnion for the barrel was too small for my barrel (the barrel was slightly oversized), so I had to "hog out" the trunnion slightly, which I discussed above in the tool section.
Remember to use a coating of lubricant on the barrel as you seat it. If you are using a press, just take it slow. The load pops are disconcerting, but normal.
At this point, you will need to check the head space, so screw the front and rear trunnions into place. DO NOT use Lock-Tite yet--you may need to remove the front trunnion again.
Before you cut the slot for the barrel pin, you need to make sure that the head space is correct. I won't get into detail on the importance of proper head space because there are plenty of articles in gun magazines and on the internet discussing the topic.
The issue we have is measuring head-space. Typically, you would want to check head-space using a "go" and a "no-go" gauge. These gauges mimic a rifle cartridge. The bolt should be able to close all the way on a "go" gauge, but not be able to fully close on the "no-go" gauge.
The problem I had is that there is apparently only one manufacturer of these gauges for 5.45x39 firearms, and the gauges each cost some $30 or $35 dollars, which seemed excessive since I was only going to be building one firearm.
I came across a work around on one of the gun boards. First, you have to fit both trunnions into the receiver, with the barrel pressed in to where you think it should be, and screw the trunnions into place. This should be enough to put the bolt and bolt carrier into place. The trigger assembly and hammer are not yet installed. You will need two cartridges. One, unmodified, will be your "go" gauge. The other will have 3 layers of transparent tape ("Scotch tape") placed over the base and trimmed around the edges. This is the "no go" gauge. I fitted these into place and closed the bolt on each, and they worked--the bolt would close on the "go" cartridge, but not close on the "no-go" cartridge.
I had seated the barrel at the correct depth so I didn't have to mess around with the barrel. However, this is the step where it is useful to have used screws, because you could simply remove the front trunnion/barrel assembly from the receiver if you had to adjust the head space.
Seating and Pinning
The next steps are fitting and pinning the rear site assembly, the gas port, and front site frame. As with the front trunnion, you made need to slightly enlarge the holes on gas port assembly and front sight to get them to fit over the barrel. Again, they should fit over the barrel, but not necessarily be easy to get on--they need to fit tight.
The 1/8 inch cutter can be used to cut the slot for larger barrel pin--just put the cutter into the pin hole and start cutting it out so that the "hole" goes all of the way through. Remember to go in from both sides, and clean out the metal. I used a standard round file to smooth things out. This will take time. I thought I had it "right," then found that the pin wouldn't go in all of the way, had to drive it out, and work some more on enlarging the slot. Sometimes getting the pin out was more challenging than the effort to get it in. It helped, on those cases, to have a block of wood with a hole bored into it. Just rest the weapon over the block so that the pin can be driven into the hole in the block, and use a hammer and punch to push the pin out. (I didn't find the press to be as useful for getting the barrel pin out as for seating it in the first instance).
The other pin slots will need the smaller diamond cutter. For a file, I used a chain saw file. Otherwise, it was the same process.
When using the file, be careful of getting them stuck. Don't twist or screw the file--always use a straight back and forth motion.
Locating the Gas Port Hole
The challenge with pushing the gas port down into position over the barrel is making sure that you have it positioned far enough back to securely hold the gas tube in place, but not so far back that the gas port hole is covered.
What I did is use a caliper and put one end over the gas port, and then put a small mark on the opposite side of the barrel with an indelible marker. There is a small hole on the bottom of gas port assembly (i.e., on the bottom side of the barrel) that I believe lines up with the opening for the gas inside the assembly. Anyway, that is the theory. I slid the gas port assembly down over the barrel until I could see the small hole. Then, using a piece of wire that I had fashioned into an L-shape, I felt around inside the assembly until I was able to push the wire through the gas port hole in the barrel. That is how I was able to check the position.
Then, checking and rechecking the fit of the gas tube and using the wire to gauge the position of the gas port hole, I tapped the assembly down until I had it in the proper position--i.e., where the gas tube was secure, but I was not covering the gas port hole.
Special Notes for the Sights
The problem you want to avoid with the sights is having them canted to one side or the other. I used a small level over the rear site assembly to get the main part of the rifle leveled, and then slid the front site assembly on the barrel with just my hand, but enough so that it would stay in place, and used the level until the sight was in place. During the process I would double-check the rear site assembly with the level to make sure I had not disturbed it. Since I had put the rear stock on prior to this, I also put it up to my shoulder just get a visual picture as well. When I thought that the front site assembly was level, I took it out of the cradle so that I could use the hammer and punch to press the front site assembly down over the barrel into its final position.
On a screw build, you will use small nuts inside the receiver to hold the screws into place. The back screw is no problem, but for the four (4) screws on the front of the trigger guard/magazine release, I found that I had to grind down the outside edge of the screw heads so they would fit, and also grind off one of the points on the nuts to get them to all fit together as well. Again, don't use Lock-Tite yet, because you may have to take the screws or nuts out to work on them.
At this point, I loosened up the screws a bit to apply some Lock-Tite and screwed them back down tight.
My next step was applying a spray-on finish to the barrel, receiver, etc. This may take several days to cure, so patience. Make sure you have removed the rear stock if you had previously installed it before applying any finish.
Trigger and Hammer Assembly
Now its time to assemble the guts of the beast. You will first want to use a soft metal (i.e., brass) cleaning brush with your Dremel to polish the trigger assembly parts--particularly where the parts will be rubbing together. Don't take off the coating, just polish it so its smooth.
I installed the pistol grip before installing the trigger assembly.
Not ever having assembled an AK trigger group before, this was an experience. It took a lot of work and patience to hold all of the parts in place against the force of the springs while sliding a pin into place. I used a small nail punch that I pushed in from one side to hold everything in alignment while I slid the pins in from the other side. (The hammer and trigger pins slide in from left to right; the "pin," rod, or whatever you want to call it for the safety lever is inserted from the right to the left).
I had two primary issues at this point. First, I didn't have enough clearance for the hammer and its spring, and it was binding against the nuts for the screws at the front of the trigger guard. I had to remove the hammer and spring, and grind a little off the top of the nuts.
Second, was fitting the spring-clip in to lock the trigger pin in place. As I noted earlier, just buy a retaining plate and don't bother with using a modified spring. Really. I modified the spring and used it just for the experience, but ....
The final step is to reattach the rear stock and install the front stock.
The first time I took it out to shoot, I put approximately 100 rounds through it without any mechanical problems. If you have read my prior posts, you know that the next time out shooting, I had a failure to extract which occurred on the first round. After taking care of that issue, I went out again and put another 90 rounds through the rifle without any further issues.
(Update Feb. 2, 2012--corrected a couple typos)