I just got a new Marlin 39A and was planning on putting an old Weaver K4 scope on it. I purchased new Weaver steel rings and mounted the scope base that came with the rifle. I noticed that the scope was visibly out of line and after removing the scope and looking closer at the base I determined that the base itself was out of line. Anyone have any experience like this? I guess I'll order a new Weaver 90 base and try again.