597 20 HB , 3rd gen mags or 22 rd Promag , they work great , the Promag trick is to insert the mag at an angle , the rear of the mag first to make contact with the bottom inside of the receiver then push the mag froward till the front of the mag is in place . The Mag has the locking notch at the rear of the mag , if you just push the mag straight up into the mag well it does not lock in very well and will be lose and wiggle .
Inserting the Promag correctly is the trick , they run like butter and the bolt hold open works every time .
My 597 20 HB is very Very accurate right out of the box , the biggest problem people have is with the 2 guide rods binding ,,,, Remember do Not Over Tighten the 2 guide rods " clamp " , just snug other wise the 2 guide rods will not flex ( move ) and the bolt will bind and cause FTF , FTE . The 3rd gen mags work great all the bugs are gone .
Just my 2 cents .