the plot thickens
Well, this is getting more complicated. I called a friend of mine earlier today who is a Class III dealer. He said there were legal semiauto M14 national match rifles for sale, and he knew of one for sale right now for $2900. I then called the shop with the M14 and told him to put my name on it, which he agreed to. I figured I would pick it up on my way home today.
After hearing more about this from you guys, though, I called BATFE's NFA division. The first guy I talked to didn't know the answer. Another guy from Firearms Technology Branch called me back about a half hour later and told me not to buy the rifle, as it's probably an illegal reweld of a demilitarized M14 receiver.
I then did a little more snooping on the 'net. I found a copy of a letter from the Chief, Firearms Technology Branch, BATF, dated August 21, 1980. It's addressed to a Mr. Martin Pearl, and says that the "manufacture of rifle receivers from demilitarized M14 rifle receivers ... is an acceptable practice." It also states that "removal of the selector pivot housing ... will remove the new receivers from the provisions of the National Firearms Act." Finally, it notes that to do this, you would need to be a licensed manufacturer, and the resulting rifle would need to be identified with a serial number and the manufacturer's name and location.
To make it even more complicated, I then found some stuff about the MKS rewelds mentioned above. The scuttlebutt is that two companies (Hahn and one other) did correctly and legally remanufacture semiauto M14s using demilitatized M14 receivers. The reports are that MKS got in trouble because it was doing the same thing as Hahn, but did it too late. Between the time that Hahn manufactured several hundred guns from demilitarized M14 receivers, and the time MKS did it, the rules changed on what constitutes acceptable demilitarization. At the time Hahn did it, a single cut was enough. By the time MKS did it, demil required a lot more. Because the receivers made by MKS were never fully demilitarized, they were illegal despite the fact that they had the selector pivot housings removed.
Note that the MKS and Hahn info above is all unverified -- it's internet chatter.
I don't know yet whether this rifle is a reweld, and if so who did the reweld. I'm going to go inspect it tonight. If it's a Hahn, then it may be a legal semiauto built on a demilitarized M14 receiver. I may or may not buy it, if I can get confirmation from BATFE that it's o.k. If it isn't, I'm not gonna touch it.