With a 590A1 equipped with a KNOXX stock you can shoot 3 inch magnum 00 Buck and 3 inch magnum slugs all day long, as long as you have the gun properly mounted. Be sure any lights etc you have are on solid though. I had my NovaTac come flying out of the T-Grip. Was fine after I added a drop of Lock Tight and tighten the screw down.
I do prefer the Federal's reduced recoil LE 2 3/4 one oz TruBall rifled slugs and Federal's reduced recoil LE 2 3/4 FlightControl 00 Buck. Here is my baby in its final set up.
The PowerPack worked excellent for raising the my cheek weld to the proper height for the Red Dot.