Sunday, October 26, 2014

Building Another AK--The Rivet Build

AK-47 Part Diagram--although this is for the AK-47, everything is pretty much the same for the AK74. (Source).

         A couple of years ago, I built an AK style rifle from a Bulgarian AK-74 parts kit. For various reasons, including ease of assembly, I chose a screw build. A friend of mine had purchased an AK-74 kit at the same time, but wanted to have it done as a rivet build like the original. However, the cost of having a gunsmith build the kits has gone up considerably since the kits could no longer be imported with barrels and a build now involves seating the barrel, gas port block, and front sight block. After not doing anything for a while, during which time he purchased a couple other AK kits, he decided to purchase the jigs and other equipment to do rivet builds. Since I had the shop press and experience, he asked me to assist with different stages of the build.

          If you plan on doing a rivet build, you really need to get the right equipment. Like me, my friend started with a receiver from Nodak Spud. Since the receiver is the "firearm" under federal law, it has to be shipped through an FFL holder who will complete the paperwork for the transfer, including the required criminal record check. Be sure to find out how much the firearms dealer will charge for a transfer fee before ordering the receiver, and don't be afraid to check around for the best price.

          My friend purchased most of his jigs and so on from AK Builder. The rivets for the front and rear trunnions were crushed with a modified bolt cutter. Apparently my friend was able to pick up parts that replaced the cutters on the bolt cutter with special jaws to crush rivets. This sufficed for crushing the rivets to hold the front trunnion and the two short rivets in the rear trunnion. The long rivet through the rear trunnion was, I believe, crushed using a separate jig and hammer. After that, he turned to me for assistance.

          When building a rivet build, the next step after riveting the front and rear trunnions is to install the barrel. With the screw build, I actually pressed the barrel before installing the trunnions, but you cannot do that with a rivet build because, once the barrel is installed, you cannot crush the rivets in the front trunnion. To press the barrel without damaging the sheet metal receiver, a special jig that supports the front trunnion in the hydraulic press is needed. Below are a couple pictures of the jig, which was ordered from AK Builder. As you can see, they get a little beat up as you use them. This support will not only be used for seating the barrel, but for seating the gas block and front sight block as well.

Support for the Front Trunnion

Support for the Front Trunnion--another view
          As you can probably guess from looking at it, the support slides through the magazine well to provide a stable support when used with the hydraulic press. The upright piece fits against the back of the front trunnion, but is shaped so you can press the barrel into place. 

          When pressing the barrel, you have to check for proper head-space. In this case, we used a set of Go/No-Go gauges.

Go and No-Go gauges
When you have pressed the barrel down close to the block in the trunnion, you simply remove the receiver from the press, insert the bolt carrier with a Go or No-Go gauge in the chamber, and attempt to close the bolt. Proper headspace is achieved when the bolt can be completely closed and locked with the Go gauge, but cannot be closed and locked with the No-Go gauge. You may have to press the barrel out slightly if you press it in too deeply, which I had to do a couple times in this case as I adjusted the seating depth.

          After the barrel is seated, it is time to cut the slot for the barrel pin, and press the barrel pin into place; then install the rear sight block (which also must have a slot cut and a pin pressed into place). I described this process in my article on the screw build--including the cutters needed--so I won't repeat that here. After you are done with that, you should have what you see below:

Ready to start on installing the gas block and front sight block.
          The next step is to install the forward band for the lower handguard. As you can see in the photo above, there are some slots about midway along the length of the barrell. This is where the band fits into place. It should fit snugly into place; you may need to use a small mallet to tap it into place. Make sure the locking lever is in the open position when you try to install it.

          Next is the gas block. As with my build, I had to use a small barrel sanding attachment with my Dremmel tool to smooth the inside of the loop and to open it up a bit. This time, I had a pipe and washer to use to press the gas port into place (whereas, in my last build, I had to slowly press it down using a punch and working it around). 

Tube and washer for pressing the gas port.
Unlike my last build, I decided to try something different for figuring the proper stopping point. Instead of marking the barrel opposite the gas port, I put the gas tube into place and simply pushed the gas block down until it fitted neatly against the gas tube. As in my prior build, I used a bent wire to verify that the block was positioned over the gas port, by inserting the bent wire into the opening for the gas tube, then pushing the wire through the gas port into the barrel, and visually verifying that the wire was protruding into the barrel.

Pressing the gas block into position.

Final position of gas block.
         The next step was to install the front sight post. As with the gas block, I had to sand the inside of the ring that fits over the barrel to clean it up and make sure it would fit over the barrel. 

          Obviously, it is important not to install the front sight block such that the post is canted to one side or another. As in my prior build, I placed the receiver into a mount that I use for holding rifles for maintenance and cleaning. Then, using a small spirit level, I verified that the rear sight block is level and slide the front sight block on by hand. Then alternating between the front sight block and the rear sight block, I used the spirit level to adjust the front sight block (tapping on one side or the other with a small mallet) until both registered as level. Although my description of the process is brief, this can actually be very time consuming.

          The fit was tight enough that I could then take it out to the press and press the block down onto the barrel. For this, I used a shorter (about 1 inch long) section of tubing over the front of the block. The front sight block was pressed down until the muzzle of the barrel is at the mouth of the ring for the front sight block. Of course, I again used the spirit level to check that the front sight block was level with the rear sight block. I also held it up to get a visual sight picture to make sure that everything--the rear sight, the gas port, and front sight--looked lined up correctly, and had my friend verify as well.

Pressing the front sight block into place.
          After this, I decided to move on to riveting the trigger guard into place. The trigger guard is held in place by four smaller rivets on the front (behind the magazine release) and a single larger rivet on the back. There is also a reinforcement plate that goes over the front four rivets. This has a stop for the safety lever, so make sure you are installing it correctly. 

          My friend had purchased a jig (yes, another one) designed to crush the rivets for the trigger guard. There is a deep slot cut into the jig to accommodate the trigger guard, with four dimples at the top for the front rivets. Because the rivet holding the magazine release lever protrudes slightly, there are channels in this slot for sliding the trigger guard into place. 

Jig, trigger guard, reinforcing plate, front rivets, and back rivet.
Unfortunately, because of the length of the rivets, you cannot simply place the rivets in the dimples and then slide the trigger guard into place. Rather, I had to tilt the trigger guard vertically, then put the rivets through the holes, then--holding the rivets so they wouldn't fall out of place--rotate the trigger guard back into a horizontal position and slide it backward into the slot in the jig until the rivet heads fit into the dimples.

You must rotate the trigger guard into a vertical position and then slide the rivets through the holes.
Front rivets and reinforcing plate.
Crush plate and insert.
           The receiver is then placed over the rivets, the crush plate inserted and slid over the four rivets, and the insert is placed vertically to push down on the crush plate. (The notch is designed to go over the central reinforcing tube in the receiver). Then the whole thing is placed into the press and pushed down to flatten the back of the rivets.

          The rear rivet is inserted from the top, so the flat portion is inside the receiver. There is another crush plate that goes underneath the receiver that has a dimple. The crush plate fits onto the shelf at the rear of the jig. Put it all back into the press and bear down! When you are done, you have this:
Riveting done!
          Although this could have been done before the riveting of the trigger guard, my next step was to cut the slots for the pins for the gas block and front sight block, and then press the pins into place. Again, I discussed what you needed for this step in my article on my earlier build.

          I will leave the finishing and installation of the hammer and trigger assembly for my friend to do on his own. Normally, you would need to finish the receiver (probably a spray on coat) and then install the hammer/trigger guts, but my friend wants to test fire it before applying the finish. Based on my advice, my friend will be using a retaining plate to hold the pins into place. (See my post on my earlier build for more on installing the trigger guts). 

          Although I know that people hold "build parties" where this is all done in an afternoon, this project really requires more time to do a nice job. I suppose that if I had the proper jigs or guides to align the sights, it could be done faster. However, this was a project that took several afternoons on weekends to complete.

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