Unless that rifle was shot a lot more than most are, I doubt the barrel is worn out. Most 742's are shot maybe 10-20 rounds a year, if that many. It would take at least 5000 rounds to really do in that barrel.
The first thing I would do is clean the barrel, and I mean really clean it, using a copper remover and an oversize bronze brush. Then check to see if the barrel could be loose (see Kenno's post). If everything basically checks out and the gun still won't shoot, or if you find the barrel is gone, I agree that rebarrelling it would not be feasible cost-wise, and you would be better retiring it and buying an new rifle.
Jim