Model 552 problem

[Fatstrat]

The barrel is loose on a 1962 vintage model 552 that I inherited from by Grandfather. Rifle still functions prefectly, but the barrel has a side to side wobble. My 1st thought was wear in the alloy receiver/barrel channel, and replaced the receiver w/one I found in VG condition. But that didn't help. Any idea what the cause of this problem might be? Thanks.