597's are almost as notorious for needing to tune the mags as High Standard pistols...
hopefully you've got the steel lip mags...
John Stimson has a great writeup online on how to tune rimfire mags...I'd suggest a search & read...
might just resolve your issue
Funny part, I tend to tune mine for CCI Minimags...they are usually the most consistant thru a chrono...
which is why I tend to use 'em for testing semi-auto actions when issues crop up...