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Old November 27, 1999, 01:57 PM   #5
Join Date: November 19, 1999
Location: Pennsylvania, USA
Posts: 22
By "Krinkov", I'm assuming you mean an AKS-74U short assault rifle, also presuming you want to do a semi-automatic version. fal308 is correct, you need a tax stamp for an SBR. Correct me if I'm wrong on this, guys, but I assume once you've got the stamp on the approved form, the stock (folding or otherwise) is no longer a concern. All this aside, get the bbl. diameter at the breech from the seller of the kit (these tend to vary w/country of manufacture). Next, find a receiver (for a realistic 74U, you'd want an AKM receiver, see if Tennesee Guns has any more MAADI receivers, or somthing similar). Get an I.D. measurement of the receivers front trunnion from the seller before you start. The measurement on the trunnion I.D. should run about .0015 - .002 under the breech O.D. of the barrel that you plan to use. Ideally, the barrel you're going to use should have never been installed onto a receiver before, otherwise you're going to have problems. Now, as you might imagine, a .002 press fit is going to be a bugger when you put that barrel in. The following works pretty good for assembly of a semi-auto AKM, and should work real well for the 74U as well. First, get yourself a set of 5,45x39.5 headspace gages - you'll need the go gage to fit the barrel and bolt, and the no-go to check your work. Measure from the front face of the receiver trunnion to the face of the stripped bolt with a depth micrometer. Record this dimention. Now, drop your go-gage into the chamber (make sure everything is good & clean), and set your depth micrometer to the measurement you just recorded and lock the mic. Place the barrel in your vice between soft jaws (breech up), place the anvil of your mic on the protruding head of the go-gage and let the rod lay along the side of the barrel. At the measuring face of the rod, you are going to want to make a really accerate scribe line as a witness mark, use a loupe and a really sharp scribe. Now, remove the gage from the barrel and chuck the barrel in the headstock of your lathe w/ the spindle locked. Leave enough sticking out of the chuck so that you can indicate the two keyways in the barrel for the forestock for // to the bed. Having done this, get a plastic milk jug cut off most of the top and a hole in the side for the barrel breech to enter. Prop the jug up on the lathe bed with wood blocks so that about 3" of breech is in the jug. Now, fill the jug with cracked dry ice and let it sit for an hour or two. Get that breech good and cold! Next, get a good helper. You're going to gently WARM that receiver trunnion with a propane torch to expand the I.D., lay a good pocket level across the receiver to keep it // with the forestock keyways. Remove the jug - you're going to slide that receiver onto the barrel, watching your level. You won't have all day to do this, so work quickly and accurately. Your helper is watching the witness mark that you scribed on the outside of the barrel through a big bench magnifier. When the front edge of the receiver trunion contacts the witness mark, your helper says "stop!". Let everything come to room temp, then check bolt lockup with your go-gage. You may have to stone a little off the back of the locking lugs to get 100% lockup. Having done this, jig up the barreled receiver in your drill press or mill, and indicate so that your barrel pin hole will be // to the top of the receiver. Pick up the spot for the hole on the receiver trunnion, and spot drill w/ a combination drill. Drill through first 1/32 u/s, then 1/64 u/s, then finish ream .001" u/s for the barrel pin. Install the remainder of the barrel components the same way, although the foresight base assy should press on without too much trouble, may require a little polishing. You can spot the gas hole through the gas block with a long twist drill that's a nice slip fit in the hole. Grind the drill back until there's only about 3/16 of flutes left, then grind the end into a bottoming drill. Use this in a drill motor and spot the hole in the barrel, then drill through w/ a jobber's length. Finish the hole to specified size. Folding stock installation on a receiver not originally equipped for it can be tricky, so get a good print from the seller and study everything before you proceed. Have fun, good luck, and KEEP IT LEGAL!

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