Spud,
Believe it or not they were trying to do you a favor. I know that them holding onto your barrel was a real downer, but I think most everyone that has the 7.62x39 has had misfires with it.
It cost me my son's first deer kill. We had sighted in the barrel & shot about 20 rounds total, but the first cartridge when his first deer (a doe) came out of the woods, I heard the hammer fall 3 times before he finally, wisely, switched shells. By that time the deer had moved and he finally got a shot at it. A falled log 6 feet in front of him, just below the line of sight, deflected the bullet up into the tops of the trees. The line on the deer with the first mismire would not have been into the log. Of the remaining box of shells, we found 6 more that were misfires. They were my handloads with 150 gr bullets, and the problem seemed to be recessed primers. Seems the 7.62x39 was made to allow for the lack of a firing pin spring and the recessed primers (and harder military primers) help to keep it from going full auto - not a problem with a single shot - of course.
I'll probably keep messing with mine & maybe try some long seated cast bullets in it and/or ream it to .303 British.
I saw that you were looking for a 7.62x39 barrel in the classifieds - good luck - there's quite a few been looking for them. I kind of fell into mine - I sent my receiver in to be fitted for a .44Mag, and a .30-30 Win barrel. They were out of .44Mag and .30-30 was going to be delayed a few weeks as well at the time (May '05, I think), (glad of that due to oversize .44 bores). So, when I called them about the delay I asked what they had - .357Mag & 7.62x39 - close enough for me.